Note: Descriptions are shown in the official language in which they were submitted.
1
COMPOSITE SUBSTRATE, METAL-COATED COMPOSITE SUBSTRATE, AND METHODS OF
PRODUCTION
THEREOF
FIELD OF THE INVENTION
[0001] The present invention relates to a composite substrate. More
specifically, the present invention is
concerned with a composite substrate comprising a mesh layer and a composite
material layer, wherein said
composite substrate can be coated in metal and then used as an electro-thermal
heating element for de-icing and
anti-icing applications.
BACKGROUND OF THE INVENTION
[0002] In the last decades, the application of composites in different
industries, especially the aerospace industry,
has been increased significantly due to their specific characteristics, such
as a high strength to weight ratio. As
polymeric composite materials comprise a high percentage of the structure of
modern aircrafts and wind turbines,
designing an appropriate de-icing and anti-icing system for such composite
structures has a high level of
importance. Different methods have been used for de-icing purposes in the
aerospace industry, including the
following: 1) bleed air de-icing systems, 2) electro-mechanical de-icing
systems, 3) electro-thermal de-icing
systems, 4) pneumatic boot systems, and 5) weeping wings.
[0003] Electro-thermal de-icing systems use electrical resistance heaters in
different forms, for example wire,
film, or foil for heating and de-icing the components of an airplane or wind-
turbine. The electro-thermal heaters
start heating the components as soon as an electrical current is applied to
them. Electro-thermal de-icers generally
have high efficiency as the generated heat in these systems flows directly
into the accumulated ice. It also has
been reported that using such de-icing systems extracts about 35% less power
from the aircraft engines compared
to conventional pneumatic systems. In addition, this type of de-icing system
typically does not add considerable
weight to the airplane, while in bleed air de-icing systems, ducting which is
used for passing the pressurized air
around the airplane adds hundreds of pounds of weight to the aircraft.
[0004] An
electro-thermal heating element for composite structures are typically
fabricated by addition, or, in
other words, the deposition of a thin metallic coating layer on top of the
composite structure using thermal spray
techniques. Thermal spray techniques are a group of techniques and processes
used for the deposition of a
metallic or non-metallic coating onto a substrate. Based on the source of
energy used for heating up and melting
the coating materials (in the form of powder, wire, rod, ceramic, or molten
materials), thermal spray processes can
be divided into three categories, in which heating and energy is provided by:
(1) combustion, (2) dissipation of
electrical energy, or (3) high-pressure gases (in the case of cold spray).
Once the coating materials are heated up,
they are accelerated toward a substrate using process gases and form a bond
with the surface. The subsequent
particles will bond with the already deposited particles and form a lamellar
structure.
Date Recue/Date Received 2020-05-15
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[0005] Thermal spray processes are widely used for enhancing thermal,
physical, mechanical, and tribological
properties of metallic substrates. However, the coating of composite materials
using thermal spray methods are
associated with some serious challenges. First of all, polymeric materials
have relatively low service temperatures
(usually less than 300 C), while in a thermal process, like plasma spraying,
the substrate temperature might easily
exceed 400 C. Furthermore, most of the treatment methods used for preparing
and roughening the metallic
substrates prior to the coating deposition process cannot be applied directly
and without any surface modification
to composites. For example, using grit blasting, in which substrates are
roughened by the impact of high-velocity
abrasive particles, for preparing the surface of a composite substrates, would
break the fibers and degrade the
mechanical properties of the composite. In addition, polymeric materials
generally have very low free surface
energy compared to metallic materials, and this deposition of a metallic
coating layer with high adhesion strength
is very difficult.
[0006] Using an appropriate preparation method prior to the coating
deposition process typically improves
the coating adhesion strength and deposition efficiency during spraying.
Different surface treatment methods have
been reported for the preparation of composite substrates. For example, grit
blasting has been used for preparing
the carbon-fiber-reinforced polymer composite (CFRP) substrate prior to the
spraying of Zn using a plasma spray
technique. After coating of CFRPs and examining their microstructure, it has
been found that a lot of fibers were
broken due to grit blasting and even some broken fibers penetrated to the
coating structure. The shear bond
strength of the coatings prepared using grit blasting has also been compared
with the coatings prepared using
abrasive papers, where it was found that using the latter preparation method
results in poor mechanical properties.
Chemical treatment is another method that has been used for preparing CFRP
substrates prior to the coating
deposition process. In this method, the substrates surface energy is increased
by exposing them to chemical
materials and solutions. Investigations into determining the effects of
surface preparation methods on the air-
plasma-sprayed Cu coatings' adhesion strength and quality have been performed,
where the CFRP substrates
were treated mechanically (grit blasting), thermally, and chemically. It has
been found that using chemical
treatment leads to better coating adhesion strengths, especially in the case
of thin film coatings. Other methods,
like the incorporation of granular particles on top of the polymeric
substrates have been used for roughening and
activating the composite substrates. Studies have been done about the
metallization of Glass-fiber-reinforced
polymer composite GFRPs for use as a heating element and de-icing
applications. During such studies, a layer of
#220 grit garnet sand and high strength epoxy adhesive mixture was applied
manually on top of a [020] ply G FRP
sample for increasing the surface roughness and consequently improving the
coating adhesion during the
deposition of a NiCrAlY coating layer using flame spray technique. The
microscopic cross-section of the NiCrAIY-
coated composite sample showed that the coating was very non-uniform. After
connecting the coated sample to a
power source for testing its performance as a heating element, it was observed
that the non-uniformity of coating
contributes to a non-uniform surface temperature distribution along the
coating surface and the formation of hot
and cold zones at the same time.
Date Recue/Date Received 2020-05-15
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[0007] The number of research studies that have been done up to now about
the thermal spray coating of
composites are very low, and in most cases, low melting-point metallic powders
(e.g. Zn and Al) have been used
as the coating materials for spraying the composites. For instance, APS
techniques have been utilized for the
deposition of Al as a bond-coat and A1203 as a top-coat onto PMC substrates
for enhancing their mechanical
properties. The metallic coatings were sprayed onto several composite
substrates using different spray parameters
(different currents and spray distances). After examining the coated samples,
it was found that the spray
parameters played a very significant role in determining the microstructure,
phase composition, and mechanical
properties of the coated samples. The maximum shear adhesion strength achieved
for the Al bond-coat was about
5.21 MPa. In another study, plasma spraying was used for the deposition of Zn,
Al, Cu, and Ni3A1 coatings onto
CFRP substrates. After the coating process, the microstructure and shear
adhesion strength of the coated samples
were analyzed. The results demonstrated that deposition of Ni3A1 and Cu leads
to the formation of delamination in
the interface of the substrate and coating due to the relatively high melting
point of coating materials and low
surface energy of the CFRP substrate. However, Al and Zn were deposited
successfully. In addition, by comparing
the plasma-sprayed Al and Zn with arch-sprayed Al and Zn, it was found that
using plasma spraying results in the
fabrication of a coating with superior mechanical properties. In another
study, a combination of plasma spraying
and cold spraying was used to deposit an aluminum coating layer onto CFRP
substrates for lightning protection
applications in aircrafts. In that study, a thin layer of aluminum coating
(about 15 pm) was deposited onto the
composite surface by using plasma spraying, and after that cold spraying was
used for the deposition of a second
aluminum layer as atop-coat. The plasma spray process was not used alone for
the deposition of the whole coating
due to the fact that the gas temperature in this process is high and it would
increase the oxidation of sprayed
particles, which would consequently increase the electrical resistivity of the
coating, which is not desirable in the
fabrication of a lightning protector coating. In addition, when the cold spray
method was used alone for the coating
of CFRPs, the coatings started peeling off once their thickness reached about
30 pm due to damage induced to
the CFRPS surface by the impact of high-velocity particles.
SUMMARY OF THE INVENTION
[0008] In accordance with the present invention, there is provided:
1. A composite substrate comprising a mesh layer and a composite material
layer, wherein the mesh layer
comprises a mesh material and an adhesive, said adhesive permeating the mesh
material and adhering
the mesh material directly to a surface of the composite material layer.
2. The composite substrate of item 1, wherein the composite material layer
comprises at least one polymeric
composite material, such as a carbon/graphite reinforced composite material, a
glass reinforced
composite material, a Kevlar reinforced composite material, or a boron
reinforced composite material.
3. The composite substrate of item 1 or 2, wherein the composite material
layer comprises a thermoplastic
composite or a thermoset composite, preferably a thermoset composite.
Date Recue/Date Received 2020-05-15
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4. The composite substrate of any one of items 1 to 3, wherein the composite
material layer comprises
reinforcing fibers embedded therein, preferably glass fibers, ceramic fibers,
or carbon fibers.
5. The composite substrate of any one of items 1 to 4, wherein the composite
material layer comprises a
glass-fiber-reinforced polymer composite (GFRP).
6. The composite substrate of item 1, wherein the composite material layer
is a polymeric composite layer,
such as a carbon/graphite reinforced composite layer, a glass reinforced
composite layer, a Keylar
reinforced composite layer, or a boron reinforced composite layer.
7. The composite substrate of item 6, wherein the composite material layer is
a thermoplastic composite
layer or a thermoset composite layer, preferably a thermoset composite layer.
8. The composite substrate of item 7, wherein the composite material layer is
a glass-fiber-reinforced
polymer composite (GFRP) layer.
9. The composite substrate of any one of items 1 to 8, wherein the mesh
material is made of carbon fibers,
ceramic fibers, glass fibers, or metal.
10. The composite substrate of any one of items 1 to 9, wherein the mesh
material is made of metal,
preferably stainless steel.
11. The composite substrate of any one of items 1 to 10, wherein the adhesion
strength of the mesh layer to
the composite material layer is between about 10 MPa and about 30 MPa,
preferably between about 14
MPa to about 22 MPa.
12. The composite substrate of any one of items 1 to 11, wherein the adhesion
strength of the mesh layer to
the composite material layer is at least about 10 MPa; at least about 12 MPa;
at least about 14 MPa; at
least about 16 MPa; or at least about 20 MPa; and/or at most about 30 MPa; at
most about 28 MPa; at
most about 26 MPa; at most about 24 MPa; at most about 23 MPa; or at most
about 22 MPa.
13. The composite substrate of any one of items 1 to 12, wherein the adhesion
strength of the metal layer to
the composite substrate is about 20 MPa or about 22 MPa.
14. The composite substrate of any one of items 1 to 13, wherein the mesh size
is at least about 50 and at
most about 700, preferably at least about 200 and at most about 400.
15. The composite substrate of any one of items 1 to 14, wherein the mesh
material has a mesh size of at
least about 50; at least about 100; at least about 150; at least about 175; or
at least about 200; and/or at
most about 700; at most about 600; at most about 500; or at most about 400.
16. The composite substrate of any one of items 1 to 15, wherein the mesh is
completely embedded in the
adhesive, such that none of the mesh material is exposed to the environment.
17. The composite substrate of any one of items 1 to 15, wherein the mesh is
partially embedded in the
adhesive, such that portions of the mesh material opposite the composite layer
are exposed to the
environment.
Date Recue/Date Received 2020-05-15
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18. The composite substrate of any one of items 1 to 15, wherein the mesh
layer has been roughened,
preferably using abrasive particles, even more preferably using abrasive grit
blasting, such that the mesh
material is at least partially exposed to the environment.
19. The composite substrate of any one of items 1 to 18, wherein the adhesive
is a thermosetting resin system
in either liquid or film form, preferably an epoxy resin such as FM300 film
adhesive.
20. A metal-coated composite substrate comprising a composite substrate as
defined in any one of items 1
to 19, and a metal layer covering a side of the mesh layer opposite the
composite layer.
21. The metal-coated composite substrate of item 20, wherein the surface of
the mesh layer opposite the
composite layer is roughened.
22. The metal-coated composite substrate of item 20 or 21, wherein the surface
roughness of the surface of
the mesh layer opposite the composite layer before the metal is deposited
thereon is between about 4
pm and about 15 pm, preferably about 7 pm and about 11 pm.
23. The metal-coated composite substrate of any one of items 20 to 22, wherein
the surface roughness of
the surface of the mesh layer opposite the composite layer before the metal is
deposited is at least about
4 pm; at least about 5 pm; at least about 6 pm; at least about 7 pm; or at
least about 8 pm; and/or at
most about 15 pm; at most about 13 pm; at most about 12 pm; or at most about
11 pm.
24. The metal-coated composite substrate of any one of items 20 to 23, wherein
the metal layer is a layer of
nickel, chromium or alloys thereof (such as FeCrAlY), including mixed NiCr
alloys, preferably NiCrAIY, or
a layer of stainless steel.
25. The metal-coated composite substrate of any one of items 20 to 24, wherein
the metal layer is a layer of
NiCrAIY.
26. The metal-coated composite substrate of any one of items 20 to 25, wherein
the metal layer is between
about 5 pm and about 150 pm thick, preferably about 30 pm and about 100 pm.
27. The metal-coated composite substrate of any one of items 20 to 26, wherein
the thickness of the metal
layer is at least about 5 pm; at least about 10 pm; at least about 20 pm; at
least about 30 pm; or at least
about 40 pm; and/or at most about 150 pm; at most about 130 pm; at most about
120 pm; at most about
110 pm; at most about 100 pm; or at most about 90 pm.
28. The metal-coated composite substrate of any one of items 20 to 27, wherein
the uniformity of the thickness
of the metal layer is between about 1% and about 10%, preferably between
about 2 and about 8%.
29. The metal-coated composite substrate of any one of items 20 to 28, wherein
the uniformity of the thickness
of the metal layer is at least about 0.5%; at least about 1%; at least about
1.5%; at least about 2%;
or at least about 2.5%; and/or at most about 15%; at most about 10%; at
most about 8%; at most
about 6%; or at most about 4%. In preferred embodiments, the porosity is
about 2.5%.
30. The metal-coated composite substrate of any one of items 20 to 29, wherein
the adhesion strength of the
metal layer to the composite substrate is between about 10 MPa and about 30
MPa, preferably between
about 14 MPa to about 22 MPa.
Date Recue/Date Received 2020-05-15
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31. The metal-coated composite substrate of any one of items 20 to 30, wherein
the adhesion strength of the
metal layer to the composite substrate is at least about 10 MPa; at least
about 12 MPa; at least about 14
MPa; at least about 16 MPa; or at least about 20 MPa; and/or at most about 30
MPa; at most about 28
MPa; at most about 26 MPa; at most about 24 MPa; at most about 23 MPa; or at
most about 22 MPa.
32. The metal-coated composite substrate of any one of items 20 to 31, wherein
the adhesion strength of the
metal layer to the composite substrate is about 20 MPa or about 22 MPa.
33. The metal-coated composite substrate of any one of items 20 to 32, wherein
the electrical resistivity of
the metal layer is between about 1.5 pQ.m and about 3 pQ.m, preferably between
about 2 pQ.m and
about 2.3 pQ.m.
34. The metal-coated composite substrate of any one of items 20 to 33, wherein
the electrical resistivity is at
least about 1.5 pQ.m; at least about 1.7 pQ.m; at least about 1.8 pQ.m; at
least about 1.9 pQ.m; or at
least about 2.0 pQ.m; and/or at most about 3.0 pQ.m; at most about 2.8 pQ.m;
at most about 2.6 pQ.m;
at most about 2.5 pQ.m; at most about 2.4 pQ.m; or at most about 2.3 pQ.m.
35. The metal-coated composite substrate of any one of items 20 to 34, wherein
the electrical resistivity of
the metal layer is about 2.3 pQ.m.
36. The metal-coated composite substrate of any one of items 20 to 35, wherein
the sheet resistance of the
metal layer is between about 0.01 Q/square and about 0.08 Q/square, preferably
between about 0.02
Q/square and about 0.06 Q/square.
37. The metal-coated composite substrate of any one of items 20 to 36, wherein
the sheet resistance is at
least about 0.01 Q/square; at least about 0.02 Q/square; at least about 0.025
Q/square; at least about
0.03 Q/square; or at least about 0.05 Q/square; and/or at most about 0.10
Q/square; at most about 0.09
Q/square; at most about 0.08 Q/square; at most about 0.07 Q/square; or at most
about 0.06 Q/square.
38. The metal-coated composite substrate of any one of items 20 to 37, wherein
the sheet resistance is about
0.058 Q/square.
39. The metal-coated composite substrate of any one of items 20 to 38, wherein
the degree of porosity of the
metal layer is between about 0.5% and about 40%, preferably between about 0.5%
and about 20%, more
preferably between about 0.5% and about 10%, even more preferably between
about 1% and about 6%.
40. The metal-coated composite substrate of any one of items 20 to 39, wherein
the porosity is at least about
0.5%; at least about 2%; at least about 5%; at least about 8%; or at least
about 10%; and/or at most about
40%; at most about 30%; at most about 20%; at most about 15%; or at most about
10%.
41. The metal-coated composite substrate of any one of items 20 to 40, wherein
the porosity is about 6.4%.
42. The metal-coated composite substrate of any one of items 20 to 41, wherein
the degree of oxidation of
the metal layer is between about 5% and about 40%, preferably between about
10% and about 32%.
43. The metal-coated composite substrate of any one of items 20 to 42, wherein
the oxidation is at least about
5%; at least about 7%; at least about 10%; at least about 15%; at least about
20%; or at least about 30%;
Date Recue/Date Received 2020-05-15
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and/or at most about 60%; at most about 50%; at most about 40%; at most about
35%; or at most about
30%.
44. The metal-coated composite substrate of any one of items 20 to 43, wherein
the oxidation is about 31.6%.
45. The metal-coated composite substrate of any one of items 20 to 44,
wherein, when a 6 amp current is
passed through the metal layer, the intensity generated in the metal layer is
at least about 1.4 KW/m2,
preferably at least about 1.6 KW/m2, more preferably at least about 1.8 KW/m2,
and most preferably about
4.3 KW/m2.
46. The metal-coated composite substrate of any one of items 20 to 45,
wherein, when a 9 amp current is
passed through the metal layer, the intensity generated in the metal layer is
at least about 3.3 KW/m2,
preferably at least about 3.6 KW/m2, more preferably at least about 4.1 KW/m2,
and most preferably about
9.6 KW/m2.
47. The metal-coated composite substrate of any one of items 20 to 46,
wherein, when a 12 amp current is
passed through the metal layer, the intensity generated in the metal layer is
at least about 5.6 KW/m2,
preferably at least about 6.5 KW/m2, more preferably at least about 7.2 KW/m2,
and most preferably about
17.2 KW/m2.
48. A method for producing the composite substrate as defined in any one of
items 1 to 19, comprising the
step of adhering a mesh material to a surface of a composite material layer
using an adhesive, said
adhesive at least partially permeating the mesh material, thereby adhering the
mesh material to the
composite material layer, and thereby producing the composite substrate.
49. The method according to item 48, wherein a preexisting coating is removed
to expose a surface the
composite material layer prior to the adhering step, after which the mesh
layer is adhered directly to said
surface of the composite material layer.
50. The method according to item 48 or 49, wherein the adhering step is
performed using vacuum bagging.
51. The method according to any one of items 48 to 50, wherein enough adhesive
is used during the adhering
step such that the mesh material is completely embedded in the adhesive and
none of the mesh material
is exposed to the environment.
52. The method according to any one of items 48 to 51, wherein a roughing step
is performed on a surface
of the mesh material opposite the composite material layer prior to the
adhering step, preferably abrasive
grit blasting, preferably with alumina grit having an average diameter of
about 80 pm.
53. The method according to item 52, wherein the roughening step exposes a
sufficient amount of the mesh
material, without removing or damaging the mesh material.
54. The method according item 52 or 53, wherein the mesh size of the mesh
material is large enough to
prevent the sand particles of the grit blasting from easily penetrating the
mesh layer.
55. A method for producing the metal-coated composite substrate as defined in
any one of items 20 to 47,
comprising the step of depositing a metal layer onto the mesh layer of the
composite substrate as defined
in any one of items 1 to 19, thereby forming the metal-coated composite
substrate.
Date Recue/Date Received 2020-05-15
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56. The method according to item 55, wherein a starting material for the metal
layer is a metal powder,
preferably a fine metal powder or a coarse metal powder.
57. The method according to item 56, wherein the metal powder is a NiCrAlY
powder, more preferably a fine
NiCrAlY powder (such as Amdry 9624, Oerlikon, size distribution: -37 +11 pm)
or a coarse NiCrAlY
powder (such as Amdry 9625, Oerlikon. size distribution: -74 +45 pm).
58. The method according to any one of items 55 to 57, wherein the depositing
step is performed using
thermal spray techniques, more preferably Air Plasma Spray (APS) techniques,
preferably using a 3MB
plasma spray gun (Sulzer Metco, Westbury, NY).
59. The method according to item 58, wherein, during thermal spraying, the
gases and particles are cooled
down, such as by using air amplifiers and air blowers to keep the substrates'
surface temperature as low
as possible during spraying (such as below the composite material layer's
curing temperature, if said layer
is a thermoset composite).
60. The method according to item 58 or 59, wherein, during the ASP, the
current used is between about 300
and about 500 A, preferably about 400 or about 500 A, more preferably about
400 A; the voltage is about
60 V; the primary gas is Argon; the primary gas flow rate is about 43.8 L/min;
the secondary gas is H2,
the secondary gas flow rate is about 6.57 L/min; the powder feed rate is
between about 30 g/min and
about 70 g/min, preferably about 32 g/min or about 64 g/min, more preferably
about 64 g/min; the spray
distance is between about 12 cm and about 16 cm, preferably about 13 cm or
about 15 cm, more
preferably about 13 cm; the robot speed is about 1 m/s, and the number of
passes is between about 3
and about 20, preferably 3, 4, 5, or 10, more preferably 3 or 4.
61. The method according to any one of items 55 to 60, wherein, before the
metal layer is deposited onto the
mesh layer of the composite substrate, the mesh layer is roughened.
62. The method according to any one of items 48 to 61, wherein the composite
material layer is provided from
an existing part or structure.
63. Use of the metal-coated composite substrate as defined in any one of items
20 to 47 as an electro-thermal
heating element, such as a de-icer or anti-icer.
64. Use of item 63 in the aerospace industry (e.g. aircrafts) or the energy
industry (e.g. wind turbines).
65. Method of using the metal-coated composite substrate as defined in any one
of items 20 to 47, the method
comprising passing a current through the metal layer so as to generate heat in
the metal layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] In the appended drawings:
FIG. 1 shows steps of a method of producing a metal-coated composite substrate
according to an embodiment of
the present invention, specifically (a) a mesh material placed on a surface of
a composite material layer, (b) a
composite substrate according to an embodiment of the present invention, (c) a
composite substrate with a
Date Recue/Date Received 2020-05-15
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roughened surface according to an embodiment of the present invention, and (d)
a metal-coated composite
substrate according to an embodiment of the present invention.
FIG. 2 shows steps of a method of producing a metal-coated composite substrate
according to an embodiment of
the present invention, using and existing part or structure, specifically (a)
a mesh material placed on a surface of
a composite material layer, (b) a composite substrate according to an
embodiment of the present invention, (c) a
composite substrate with a roughened surface according to an embodiment of the
present invention, and (d) a
metal-coated composite substrate according to an embodiment of the present
invention.
FIG. 3 shows a method of use of a metal-coated composite substrate according
to an embodiment of the present
invention, specifically (a) a method of use of a metal-coated composite
substrate made from a newly fabricated
structure or part, and (b) a method of use of a metal-coated composite
substrate made from an existing structure
or part.
FIG. 4 shows (a) a 200 mesh plate according to an embodiment of the present
invention, (b) a 400 mesh plate
according to an embodiment of the present invention, and (c) a conventional
composite plate.
FIG. 5 shows a grit-blasted 200 mesh substrate after coating according to an
embodiment of the present invention.
FIG. 6 shows a schematic view of four-point probe method.
FIG. 7 shows low magnification (left side) and high magnification (right side)
microscopic images of the cross-
section of a) a 200 mesh substrate according to an embodiment of the present
invention and b) a 400 mesh
substrate according to an embodiment of the present invention after
fabrication.
FIG. 8 shows a conventional composite substrate after grit blasting.
FIG. 9 shows confocal images of the top surface of the grit-blasted 200 mesh
substrates according to an
embodiment of the present invention using different grit-blasting parameters,
specifically (a) 76 psi and 200
seconds; (b) 50 psi and 90 seconds; and (c) 76 psi and 150 seconds.
FIG. 10 shows confocal images of the top surface of the grit-blasted 400 mesh
substrates according to an
embodiment of the present invention using different grit-blasting parameters,
specifically (a) 76 psi and 90 seconds;
(b) 60 psi and 80 seconds; and (c) 66 psi and 180 seconds.
FIG. 11 shows burnt samples after coating, (a) a conventional composite
substrate, (b) 200 mesh substrate without
grit blasting according to an embodiment of the present invention, and (c)
grit-blasted 200 mesh substrate
according to an embodiment of the present invention.
FIG. 12 shows cross-sections of a coated grit-blasted 400 mesh substrate
according to an embodiment of the
present invention (a) low magnification, and (b) high magnification.
FIG. 13 shows cross sections of a) grit-blasted conventional composite, b) a
not grit-blasted 200 mesh according
to an embodiment of the present invention, c) a grit-blasted 200 mesh
according to an embodiment of the present
invention, and d) a grit-blasted 400 mesh substrate after coating according to
an embodiment of the present
invention.
Date Recue/Date Received 2020-05-15
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FIG. 14 shows a cross-section of a coated (a) grit-blasted 400 mesh substrate
according to an embodiment of the
present invention, (b) grit-blasted 200 mesh substrate according to an
embodiment of the present invention, and
(c) a grit-blasted conventional stainless steel block with high magnification.
FIG. 15 shows cross-sections of (a) a grit-blasted 200 mesh substrate
according to an embodiment of the present
invention, and (b) a coated grit-blasted 400 mesh substrate according to an
embodiment of the present invention.
FIG. 16 shows cross-sections of (a) and (c) a grit-blasted 200 mesh substrate
according to an embodiment of the
present invention with low and high magnifications, (b) and (d) a grit-blasted
400 mesh substrate according to an
embodiment of the present invention with low and high magnifications.
FIG. 17 shows cross-sections of a coated grit-blasted 200 mesh substrate
according to an embodiment of the
present invention with, (a) low, and (b) high magnifications.
FIG. 18 shows adhesion strength results of the coated samples according to
embodiments of the present invention.
FIG. 19 shows failure modes in coated samples according to embodiments of the
present invention in which, (a) a
400 mesh composite, and (b) a 200 mesh composite were used as the substrate.
FIG. 20 shows V-I graphs of the coated composite samples according to
embodiments of the present invention.
FIG. 21 shows generated intensity in the coated samples according to
embodiments of the present invention for
different current values.
FIG. 22 shows infrared pictures of the surface temperature distribution of the
coatings according to embodiments
of the present invention with (a) non-uniform, and (b) uniform thicknesses.
DETAILED DESCRIPTION OF THE INVENTION
[0010] There is provided a composite substrate comprising a mesh layer and a
composite material layer, wherein
the mesh layer comprises a mesh material and an adhesive, said adhesive
permeating the mesh material so as to
adhere the mesh material to the composite material layer. There is also
provided a method for producing said
composite substrate.
[0011] The present inventors discovered that a composite substrate comprising
a mesh layer makes for an
effective substrate on which to apply a metal coating, as the mesh material
will protect the underlying composite
material layer during the coating process and at the same time will act as an
anchor to keep the eventual metal
coating on the surface of the composite substrate. Once coated with a metal
layer, the composite substrate makes
for an effective electro-thermal heating element, such as a de-icer or anti-
icer.
[0012] The present inventors have also discovered a process of producing the
above composite substrate, as
well as a process for coating said composite substrate with a metal layer.
Specifically, the inventors have
discovered effective coating parameters with which the metal layer can be
applied to the composite substrate. Said
coating parameters allow for the deposition of a metal layer that is of
sufficiently uniform thickness, with strong
adhesion strength to the composite substrate, with high mechanical strength,
high resistance to galvanic corrosion,
and/or with high electrical resistivity. This process may also allow for high
deposition efficiency.
Date Recue/Date Received 2020-05-15
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[0013] This composite substrate, the metal-coated composite substrate, and the
processes for producing the
composite substrate and the metal-coated composite substrate create new
opportunities for the design of electro-
thermal heating elements, such as a de-icers or anti-icers.
Composite substrate comprising a mesh layer and a composite material layer
[0014] In a first aspect of the invention, a composite substrate comprising a
mesh layer and a composite material
layer is provided, wherein the mesh layer comprises a mesh material and an
adhesive, said adhesive permeating
the mesh material and adhering the mesh material directly to a surface of the
composite material layer.
[0015] As stated, the composite substrate comprises a mesh layer and a
composite material layer. As previously
stated, the composite substrate of the present invention is intended to be
used as a substrate on which to apply a
metal coating, as the mesh material will protect the underlying composite
material layer during the coating process
and at the same time will act as an anchor to keep the metal coating on the
surface of the composite substrate.
[0016] The dimensions of the composite substrate will largely be determined by
the dimensions of the mesh
layer and the composite material layer. The skilled person would understand
that the composite substrate could
come in a variety of sizes and shapes depending on the desired applications
thereof. For example, if the composite
substrate is intended to be used as part of a blade of a wind turbine, then
the composite substrate will be
dimensioned and sized for that purpose.
[0017] The composite material layer of the composite substrate refers to the
layer of material underlying the
mesh layer. It is to be understood that the composite material layer may be
made of a variety of materials,
depending on the desired applications thereof. The shape, size, and thickness
of the composite substrate and the
composite material layer will also be determined by the intended application
of the composite substrate. For
example, if the composite substrate is intended to be used as part of a blade
of a wind turbine, then the composite
material layer can be made of composite polymer materials typically used for
such an application; the composite
material layer will also be dimensioned and sized to be used as part of a
blade of a wind turbine. The composite
material layer can also be the surface of an object, for example the surface
of the blade of a wind turbine.
[0018] In embodiments, the composite material layer comprises polymeric
composite materials. Examples of
polymeric composite materials include carbon/graphite reinforced composite
materials, glass reinforced composite
materials, Keylar reinforced composite materials and boron reinforced
composite materials. In preferred
embodiments, the composite material layer comprises a thermoplastic composite
or a thermoset composite,
preferably a thermoset composite.
[0019] In preferred embodiments, the composite material layer comprises
reinforcing fibers embedded therein,
preferably glass fibers, ceramic fibers, or carbon fibers. Said reinforcing
fibers are typically used to increase the
mechanical strength of such composite materials. The composite material layer
can comprise a dispersion of
reinforcing fibers in a matrix, preferably a polymer matrix. In a more
preferred embodiment, the composite material
layer comprises a glass-fiber-reinforced polymer composite (GFRP).
Date Recue/Date Received 2020-05-15
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[0020] The mesh layer is a layer of the composite substrate that comprises a
mesh material that has been
adhered to the composite material layer using an adhesive. In order to
properly secure the mesh material to the
composite material layer, the adhesive permeates the mesh material.
[0021] As previously stated, when a metal coating is applied to the composite
substrate, the mesh material of
the mesh layer will protect the underlying composite material layer during the
coating process (namely during grit
blasting and other similar surface preparation processes) and at the same time
will act as an anchor to keep the
metal coating on the surface of the composite substrate. A mesh material is
typically made of a woven wire. For
the purposes of the present invention, the mesh material is made of
sufficiently strong material that can be properly
adhered to the composite material layer using an adhesive, and that can
properly anchor any intended metal
coatings. In embodiments, the mesh material is made of carbon fibers, ceramic
fibers, glass fibers, or metal. In
preferred embodiments, the mesh material is made of metal, preferably
stainless steel.
[0022] The mesh size of the mesh material will influence various properties of
both the composite substrate and
any metal coating that may be deposited thereon (see below for more detail).
Mesh size typically refers to the
number of openings in the material per one linear inch of material. For
example, a mesh material with a mesh size
of 100 has 100 openings per linear inch of material. The mesh size of the mesh
material should be small enough
so as to allow the chosen adhesive to penetrate and permeate the mesh
material, as this will help adhere the mesh
material to the composite material layer, and it will facilitate the process
of producing the composite substrate of
the present invention (as the adhesive can be applied to the mesh material
after the mesh material has been
placed on the top surface of the composite material layer, such that the
adhesive will penetrate the mesh material
and come into contact with the composite material layer).
[0023] In general, the size of the mesh affects the resulting adhesion
strength between the mesh layer and the
composite material layer. In embodiments, the adhesion strength of the mesh
layer to the composite material layer
is between about 10 MPa and about 30 MPa, preferably between about 14 MPa to
about 22 MPa. In embodiments,
the adhesion strength of the mesh layer to the composite material layer is at
least about 10 MPa; at least about 12
MPa; at least about 14 MPa; at least about 16 MPa; or at least about 20 MPa;
and/or at most about 30 MPa; at
most about 28 MPa; at most about 26 MPa; at most about 24 MPa; at most about
23 MPa; or at most about 22
MPa. In preferred embodiments, the adhesion strength of the metal layer to the
composite substrate is about 20
MPa or about 22 MPa. For clarity, the above-listed adhesion strength values
are measured using a flatwise tensile
test, preferably as described in the experimental section below.
[0024] While lower mesh sizes generally improve adhesion strength, the mesh
size should be sufficiently high to
allow the mesh material to better protect the underling composite material
layer. For example, if the composite
substrate is subjected to abrasive grit blasting in order to roughen the
surface thereof, it is important that the mesh
hole dimensions be smaller than the grit blasting sand diameter, so as to
prevent the sand from easily penetrating
the mesh layer and reaching the composite material layer, as this could damage
the composite material layer.
[0025] In embodiments, the mesh size is at least about 50 and at most about
700, preferably at least about 200
and at most about 400. In embodiments, the mesh material has a mesh size of at
least about 50; at least about
Date Recue/Date Received 2020-05-15
13
100; at least about 150; at least about 175; or at least about 200; and/or at
most about 700; at most about 600; at
most about 500; or at most about 400.
[0026] The adhesive used must sufficiently adhere the mesh material to the
composite material layer. In addition,
in embodiments, the mesh is completely embedded in the adhesive, such that
none of the mesh material is
exposed to the environment. In alternative embodiments, the mesh is partially
embedded in the adhesive, such
that portions of the mesh material opposite the composite layer are exposed to
the environment.
[0027] Also, the adhesive should be a material that can be sufficiently
roughened or removed without removing
or damaging the mesh material. For example, in the event that the composite
substrate of the present invention is
subjected to abrasive grit blasting, the adhesive should be chosen such that
said adhesive can be roughened and
partially removed, thereby exposing more of the mesh material.
[0028] In embodiments, the mesh layer of the composite substrate of the
present invention has been roughened,
preferably using abrasive particles, even more preferably using abrasive grit
blasting, such that the mesh material
is at least partially exposed to the environment (see subsequent section for
more details).
[0029] The skilled person would understand that the adhesive can be a variety
of adhesives known in the art. In
embodiments, the adhesive can be different types of thermosetting resin
systems in either liquid or film forms,
preferably an epoxy resin such as FM300 film adhesive.
[0030] The thickness of the mesh layer will generally be about as thick as the
mesh material, although the
thickness of the layer may increase depending on how much adhesive is used.
[0031] The mesh layer is adhered directly to the composite material layer.
This means that there are no additional
layers of material between the composite material layer and the mesh layer.
Metal-coated composite substrate comprising a metal layer, a mesh layer and a
composite material layer
[0032] In another aspect of the present invention, a metal-coated composite
substrate is provided. The metal-
coated composite substrate comprises a composite substrate, as defined in the
section above, and a metal layer
covering a side of the mesh layer opposite the composite layer.
[0033] As stated, the composite substrate of the metal-coated composite
substrate is as defined in the section
above. However, it should be mentioned that, if the mesh layer of the
composite substrate has not been roughened,
the surface of the mesh layer will preferably be roughened before the metal
layer can be applied. The roughening
of the mesh layer will expose the mesh material, thereby allowing the mesh
material to better anchor the metal
layer, thereby allowing for a better adhesion of the metal layer to the
composite substrate.
[0034] In general, the higher the surface roughness of the mesh layer before
the metal layer is applied, the better
the adhesion strength of the metal layer to the mesh layer. In embodiments,
the surface roughness of the mesh
layer before the metal is deposited is between about 4 pm and about 15 pm,
preferably about 7 pm and about 11
pm. In embodiments, the surface roughness of the mesh layer before the metal
is deposited is at least about 4
Date Recue/Date Received 2020-05-15
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pm; at least about 5 pm; at least about 6 pm; at least about 7 pm; or at least
about 8 pm; and/or at most about
15 pm; at most about 13 pm; at most about 12 pm; or at most about 11 pm.
[0035] The metal layer can be made of a variety of metals. It should be noted
that, as the metal-coated composite
substrate of the present invention is intended to be used as an electro-
thermal heating element, it is preferable that
the selected metal has sufficiently high electronic resistivity such that it
can more easily generate heat. In addition,
the selected metal should be sufficiently resistive to galvanic corrosion and
should have sufficient mechanical
strength for use as an electro-thermal heating element. However, the skilled
person would understand that different
metals and alloys may possess different advantages and disadvantages in terms
of electronic resistivity, galvanic
corrosion, and mechanical strength. Accordingly, while it is preferable that
the metal used will have high electronic
resistivity, high resistance to galvanic corrosion, and high mechanical
strength, the skilled person would understand
other metals may be used depending on the intended applications of the metal-
coated composite substrate.
[0036] In preferred embodiments, the metal layer is a layer of nickel,
chromium or alloys thereof (such as
FeCrAlY), including mixed NiCr alloys, preferably NiCrAlY, or a layer of
stainless steel. In a most preferred
embodiment, the metal layer is a layer of NiCrAlY. One advantage of using
NiCrAlY is that the electrical resistance
of the NiCrAlY layer is almost constant and independent of the coating surface
temperature (at least from 25 to
150 C).
[0037] The thickness of the metal layer will affect the properties of the
resulting metal-coated composite
substrate. In general, if the metal layer is too thick, the metal coating may
not sufficiently adhere to the composite
substrate. Indeed, in general, the metal layer adhesiveness to the composite
substrate decreases with increasing
thickness. In addition, a higher thickness will generally lower the electrical
resistance of the metal layer.
[0038] In embodiments, the metal layer is between about 5 pm and about 150 pm
thick, preferably about 30 pm
and about 100 pm. In embodiments, the thickness of the metal layer is at least
about 5 pm; at least about 10 pm;
at least about 20 pm; at least about 30 pm; or at least about 40 pm; and/or at
most about 150 pm; at most about
130 pm; at most about 120 pm; at most about 110 pm; at most about 100 pm; or
at most about 90 pm.
[0039] In preferred embodiments, the metal layer is relatively uniform in
thickness. This will allow for more
uniform surface temperature distribution in the event that the metal-coated
composite substrate is used as an
electro-thermal heating element. In embodiments, the uniformity of the
thickness of the metal layer is between
about 1% and about 10%, preferably between about 2 and about 8%. In
embodiments, the uniformity of the
thickness of the metal layer is at least about 0.5%; at least about 1%; at
least about 1.5%; at least about 2%;
or at least about 2.5%; and/or at most about 15%; at most about 10%; at
most about 8%; at most about 6%;
or at most about 4%. In preferred embodiments, the porosity is about 2.5%.
[0040] As mentioned, the presence of the metal mesh layer improves the
adhesion of the metal layer to the
composite substrate. This is important because it will reduce the likelihood
of, and preferably prevent, the metal
layer from tearing off when the metal-coated composite substrate is in use,
for example as an electro-thermal
heating element. In embodiments, the adhesion strength of the metal layer to
the composite substrate is between
Date Recue/Date Received 2020-05-15
15
about 10 MPa and about 30 MPa, preferably between about 14 MPa to about 22
MPa. In embodiments, the
adhesion strength of the metal layer to the composite substrate is at least
about 10 MPa; at least about 12 MPa;
at least about 14 MPa; at least about 16 MPa; or at least about 20 MPa; and/or
at most about 30 MPa; at most
about 28 MPa; at most about 26 MPa; at most about 24 MPa; at most about 23
MPa; or at most about 22 MPa. In
preferred embodiments, the adhesion strength of the metal layer to the
composite substrate is about 20 MPa or
about 22 MPa. For clarity, the above-listed adhesion strength values are
measured using a flatwise tensile test,
preferably as described in the experimental section below.
[0041] As mentioned, it is preferable that the metal layer has high electrical
resistivity, as this will allow the metal
layer to more effectively generate heat. It should be noted that electrical
resistivity is directly proportional to
electrical resistance. However, resistivity is an intrinsic property that
unlike electrical resistance does not depend
on the shape and dimensions of the material in question.
[0042] In embodiments, the electrical resistivity of the metal layer is
between about 1.5 pQ.m and about 3 pQ.m,
preferably between about 2 pQ.m and about 2.3 pQ.m. In embodiments, the
electrical resistivity is at least about
1.5 pQ.m; at least about 1.7 pQ.m; at least about 1.8 pQ.m; at least about 1.9
pQ.m; or at least about 2.0 pQ.m;
and/or at most about 3.0 pQ.m; at most about 2.8 pQ.m; at most about 2.6 pQ.m;
at most about 2.5 pQ.m; at
most about 2.4 pQ.m; or at most about 2.3 pQ.m. In preferred embodiments, the
electrical resistivity of the metal
layer is about 2.3 pQ.m.
[0043] It should be noted that it is also preferable for the metal layer to
have high sheet resistance, which is a
parameter used more frequently to characterize thin coatings. One distinction
between sheet resistance and
electrical resistance is that sheet resistance, much like electrical
resistivity, is independent of size, thereby making
it easier to compare the effectiveness of layers of differing thicknesses. In
embodiments, the sheet resistance of
the metal layer is between about 0.01 Q/square and about 0.08 Q/square,
preferably between about 0.02
Q/square and about 0.06 Q/square. In embodiments, the sheet resistance is at
least about 0.01 Q/square; at least
about 0.02 Q/square; at least about 0.025 Q/square; at least about 0.03
Q/square; or at least about 0.05
Q/square; and/or at most about 0.10 Q/square; at most about 0.09 Q/square; at
most about 0.08 Q/square; at
most about 0.07 Q/square; or at most about 0.06 Q/square. In preferred
embodiments, the sheet resistance is
about 0.058 Q/square.
[0044] For clarity, the above-listed electrical resistance, electrical
resistivity, and sheet resistance values are
measured using a four-point electrical probe technique, preferably as
described in the experimental section below.
[0045] The skilled person would understand that various properties of the
metal layer will affect its electronic
resistivity, mechanical strength, and/or resistance to galvanic corrosion. For
example, a higher degree of porosity
and a higher degree of oxidation in the metal layer will generally increase
electrical resistivity.
[0046] In embodiments, the degree of porosity of the metal layer is between
about 0.5 and about 40%, preferably
between about 0.5 and about 20%, more preferably between about 0.5 and about
10%, even more preferably
between about 1% and about 6%. In embodiments, the porosity is at least about
0.5%; at least about 2%; at least
Date Recue/Date Received 2020-05-15
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about5%; at least about 8%; or at least about 10%; and/or at most about 40%;
at most about 30%; at most about
20%; at most about 15%; or at most about 10%. In preferred embodiments, the
porosity is about 6.4%.
[0047] In embodiments, the degree of oxidation of the metal layer is between
about 5% and about 40%,
preferably between about 10% and about 32%. In embodiments, the oxidation is
at least about 5%; at least about
7%; at least about 10%; at least about 15%; at least about 20%; or at least
about 30%; and/or at most about 60%;
at most about 50%; at most about 40%; at most about *35%; or at most about
30%. In preferred embodiments, the
oxidation is about 31.6%.
[0048] When acting as a heating element, current is passed through the metal
layer of the metal-coated
composite substrate so as to cause the metal layer to generate heat. In
preferred embodiments, when a 6 amp
current is passed through the metal layer, the intensity generated in the
metal layer is at least about 1.4 KW/m2,
preferably at least about 1.6 KW/m2, more preferably at least about 1.8 KW/m2,
and most preferably about 4.3
KW/m2. Similarly, in preferred embodiments, when a 9 amp current is passed
through the metal layer, the intensity
generated in the metal layer is at least about 3.3 KW/m2, preferably at least
about 3.6 KW/m2, more preferably at
least about 4.1 KW/m2, and most preferably about 9.6 KW/m2. Similarly, in
preferred embodiments, when a 12 amp
current is passed through the metal layer, the intensity generated in the
metal layer is at least about 5.6 KW/m2,
preferably at least about 6.5 KW/m2, more preferably at least about 7.2 KW/m2,
and most preferably about 17.2
KW/m2.
[0049] For clarity, the above-listed intensity values are measured using a
four-point electrical probe technique
(and the equation Intensity = = ¨A1 RI2), preferably as described in the
experimental section below.
[0050] Generally, the amount of intensity needed to be provided by the heating
elements for de-icing purposes
is in the range of 2.1-3.6 kW/m2. Accordingly, the current used to generate
heat in the metal layer can be modified
depending on the characteristics of the metal layer. In general, though, it is
preferable that the electrical resistivity
of the metal layer be higher so that less current needs to be used to generate
sufficient heat for de-icing or anti-
icing purposes.
Optional additional layers
[0051] In embodiments, the metal-coated composite substrate further comprises
one or more additional layer(s)
on a side of the metal layer opposite the mesh layer. It is preferable that
these layers be as thin as possible,
preferable between about 5 microns to about 10 microns, in order to avoid
adding too much weight to the metal-
coated composite substrate, as well as to ensure that the metal layer is as
close to the external surface of the
metal-coated composite substrate as possible. This is because, if the metal-
coated composite substrate is to
function as an electrothermal heating element, the portion of the metal-coated
composite substrate that will
generate heat (i.e. the metal layer) should be as close as possible to where
ice is likely to form. If additional layers
are too thick, this will prevent heat from reaching the external surface of
the metal-coated composite substrate.
Date Recue/Date Received 2020-05-15
17
Method of producing composite substrate comprising a mesh layer and a
composite material layer
[0052] In another aspect of the invention, a method for producing the above
composite substrate comprising a
mesh layer and a composite material layer is provided.
[0053] The method for producing the composite substrate thus comprises the
step of:
adhering a mesh material to a surface of a composite material layer using an
adhesive, said
adhesive at least partially permeating the mesh material, thereby adhering the
mesh material to
the composite material layer, and thereby producing the composite substrate.
Starting Materials
[0054] The starting materials can be the composite material layer, the mesh
material, and the adhesive as
defined in the previous section. It is generally understood that the resulting
composite substrate can be modified
for use as an electrothermal heating element (by depositing a metal layer
thereon). Accordingly, the composite
material layer can be provided by manufacturing and dimensioning a composite
material layer according to the
intended use of the composite substrate.
[0055] It is also understood that the above method can be used on existing
parts and structures. This means
that said existing parts and structures may be used as the composite material
layer. However, if the existing part
or structure has a preexisting coating (for example, an adhesive film has
already been formed on the existing
composite material layer), it is preferable that said preexisting coating be
removed before the above method is
performed to expose a surface of the composite material layer. This removal of
the preexisting coating can be
done using any known technique in the art (such as sand blasting), as long as
it does not damage the underlying
composite material layer.
[0056] As an example, many existing wind turbine blades are made of composite
materials (i.e. a composite
material layer), yet they do not comprise the composite substrate of the
present invention. The above method can
be used to modify said wind turbine blades so as to transform the existing
composite material layer into the
composite substrate of the present invention. If the existing composite
material layer of the wind turbine already
has a preexisting coating thereon (for example, an adhesive film), then said
layer should be removed (for example,
by sand blasting) before the above method is performed. This removal of
preexisting coatings will help lighten the
resulting composite substrate, and it will enable the mesh layer to be in
direct contact with the composite material
layer.
[0057] It is also understood that each of the composite material layer, the
mesh material, and the adhesive can
be provided and/or manufactured using any known method in the art.
Adhering step
[0058] In this step, the mesh material is adhered to the surface of a
composite material layer using an adhesive,
thereby forming the mesh layer. As mentioned previously, in order to increase
the adhesion strength of the mesh
Date Recue/Date Received 2020-05-15
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material to the composite material layer, the adhesive should permeate the
mesh material as much as possible.
This step can be performed using any known method in the art.
[0059] In preferred embodiments, the adhering step is performed using vacuum
bagging. Vacuum bagging
typically consists of four primary items, including peel ply and release film,
breather and bleeder cloth, vacuum
bagging film, and a vacuum pump. After vacuum bagging, the setup can be
transferred to an autoclave for a curing
process under the sufficient pressure and temperature.
[0060] As mentioned in the previous section, in preferred embodiments, enough
adhesive should be used such
that the mesh material is completely embedded in the adhesive and none of the
mesh material is exposed to the
environment.
Optional roughing step
[0061] As mentioned previously, the surface of the mesh layer can be
roughened. This can be done using any
known technique in the art, preferably abrasive grit blasting, preferably with
alumina grit having an average
diameter of about 80 pm. The resulting surface roughness of the composite
substrate can be as defined in the
previous sections.
[0062] As mentioned, the roughening of the mesh layer will expose the mesh
material, thereby allowing the mesh
material to better anchor a metal layer that will be formed, thereby allowing
for a better adhesion of the metal layer
to the composite substrate. Therefore, it is preferable that the roughening
step expose a sufficient amount of the
mesh material, without removing or damaging the mesh material.
[0063] When abrasive grit blasting is used, it is preferable to optimize the
parameters of the abrasive grit blasting.
However, the optimal parameters of the abrasive grit blasting will depend on
the adhesive used and the mesh
material used. For example, when a 200 steel mesh is used with an epoxy resin
adhesive, the abrasive grit blasting
should ideally be performed with a pressure of about 76 psi and for about 150
seconds. However, a pressure of
76 psi and a time of 200 seconds may damage or remove the steel wires, while a
pressure of 50 psi and a time of
90 seconds could not remove enough epoxy to sufficiently expose the mesh
material, thereby having a negative
impact on coating adhesion and deposition efficiency of a metal layer.
[0064] Similarly, when a 400 steel mesh is used with an epoxy resin adhesive,
the abrasive grit blasting should
ideally be performed with a pressure of about 66 psi and for about 180
seconds. However, a pressure of 76 psi
and a time of 90 seconds may damage or remove the steel wires, while a
pressure of 60 psi and a time of 80
seconds could not remove enough epoxy to sufficiently expose the mesh
material, thereby having a negative
impact on coating adhesion and deposition efficiency of a metal layer.
[0065] In general, mesh materials with lower mesh sizes are less sensitive and
vulnerable to grit blasting, as
their wires are thicker and more resistant to the impact of high-velocity
particles. In addition, lower mesh sizes
generally result in higher surface roughness. This might be due to the
relatively larger voids existing on mesh
materials with lower mesh sizes. Accordingly, in general, using mesh materials
of lower mesh sizes (for example,
Date Recue/Date Received 2020-05-15
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a mesh size of 200 compared to a mesh size of 400) results in a better coating
deposition and adhesion during
spraying of a metal layer.
[0066] As mentioned in the previous sections, the mesh layer protects the
composite material layer during the
roughening step. Accordingly, when grit blasting is used, it is preferable
that the mesh size be large enough to
prevent the sand particles of the grit blasting from easily penetrating the
mesh layer, as this would result in damage
to the composite material layer.
[0067] The skilled person would understand that, in general, increasing the
pressure and time of abrasive grit
blasting would remove more resin from the mesh layer, while decreasing the
pressure and time of abrasive grit
blasting will remove less resin.
[0068] If another roughening method is used other than abrasive grit blasting,
the optimal parameters of said
roughening method should be determined so as sufficiently roughen the mesh
layer and expose a sufficient amount
of the mesh material, without removing or damaging the mesh material.
Method of producing a metal-coated composite substrate comprising a metal
layer, a mesh layer and a
composite material layer
[0069] In another aspect of the invention, a method for producing the above
metal-coated composite substrate
comprising a metal layer, a mesh layer and a composite material layer is
provided.
[0070] The method for producing the metal-coated composite substrate thus
comprises the step of:
depositing a metal layer onto the mesh layer of the composite substrate as
defined in the
previous section, thereby forming the metal-coated composite substrate.
Starting Materials
[0071] The starting materials can be the composite substrate as defined in the
previous section. It is generally
understood that the resulting metal-coated composite substrate can be used as
an electrothermal heating element.
Accordingly, the composite substrate can be provided by manufacturing and
dimensioning a composite substrate
according to the intended use of the metal-coated composite substrate.
[0072] As for the metal layer, the starting material can be any metal defined
in the previous sections. As
mentioned, the metal chosen will depend on the intended use of the metal-
coated composite substrate, but
generally it is preferable for the chosen metal to have high electric
resistivity, high mechanical strength, and high
resistance to galvanic corrosion. Preferably, the starting material for the
metal layer is a metal powder, preferably
a fine metal powder or a coarse metal powder. In preferred embodiments, the
metal powder is a NiCrAlY powder,
more preferably a fine NiCrAlY powder (such as Amdry 9624, Oerlikon, size
distribution: -37 +11 pm) or a coarse
NiCrAlY powder (such as Amdry 9625, Oerlikon. size distribution: -74 +45 pm).
[0073] The choice of starting material for the metal layer (for example, fine
vs coarse metal powder) will
somewhat affect the resulting metal layer that is formed on the composite
substrate (see the following section for
Date Recue/Date Received 2020-05-15
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more details and examples). In general, using fine metal powders (as opposed
to coarse metal powders) tends to
result in a metal layer with lower porosity, higher oxidation, lower
deposition efficiency (as in, when spray coating
techniques are used, more passes are needed to arrive at coatings of similar
thickness as those achieve with
coarse metal powders), and tends to require fewer passes to achieve a
relatively uniform thickness. However,
overall, the use of finer metal powders tends to result in a metal layer of
lower electronic resistivity (this could be
because porosity likely affects resistivity more strongly than oxidation).
Depositing step
[0074] In this step, the metal layer is deposited onto the mesh layer of the
composite substrate, thereby forming
the metal-coated composite substrate. The resulting metal layer is as defined
in the sections above. While this
step can be performed using any known method in the art, it is preferable to
use thermal spray techniques, more
preferably Air Plasma Spray (APS) techniques, preferably using a 3MB plasma
spray gun (Sulzer Metco, Westbury,
NY).
[0075] If ASP techniques are used, the composite substrate (specifically the
composite material layer) may be
vulnerable to the high-temperature gases used and the impact of high-
temperature particles. Accordingly, in
preferred embodiments, the gases and particles are advantageously cooled down,
such as by using air amplifiers
and air blowers to keep the substrates surface temperature as low as possible
during spraying (such as below the
composite material layer's curing temperature, if said layer is a thermoset
composite).
[0076] The parameters of the ASP used will naturally affect the resulting
metal layer. In general, such parameters
include current, voltage, primary gas (including flow rate thereof), secondary
gas (including flow rate thereof),
powder feed rate, spray distance, robot speed, and number of passes.
[0077] In preferred embodiments, the current used is between about 300 and
about 500 A, preferably about 400
or about 500 A, more preferably about 400 A; the voltage is about 60 V; the
primary gas is Argon; the primary gas
flow rate is about 43.8 L/min; the secondary gas is H2; the secondary gas flow
rate is about 6.57 L/min; the powder
feed rate is between about 30 g/min and about 70 g/min, preferably about 32
g/min or about 64 g/min, more
preferably about 64 g/min; the spray distance is between about 12 cm and about
16 cm, preferably about 13 cm
or about 15 cm, more preferably about 13 cm; the robot speed is about 1 m/s,
and the number of passes is between
about 3 and about 20, preferably 3, 4, 5, or 10, more preferably 3 or 4.
[0078] The skilled person would understand that the above parameters could be
modified, and that said
modifications may affect the resulting metal layer. What is important is that
the resulting metal layer conforms to
the definition provided above, that the metal layer is sufficiently strongly
adhered to the composite substrate, and
that the composite substrate is not damaged during the deposition process.
[0079] For example, if the current is too high, the powder feed rate is too
high, or the spray distance is too low,
the composite substrate may end up being burnt. However, if the current is
high, other parameters can be adjusted
(for example, the powder feed rate can be lowered, or the spray distance can
be increased) in order to compensate
(although this may impact other aspects of the deposition, such as deposition
efficiency). What matters is that the
Date Recue/Date Received 2020-05-15
21
surface temperature of the composite substrate does not become so hot so as to
damage or burn the composite
substrate.
[0080] As mentioned previously, the choice of metal powder, as well as the
spray parameters, will affect the
resulting metal layer. For example, increasing the number of passes will
obviously increase the thickness of the
resulting metal layer. However, if a coarse metal powder is used, each pass
will increase the thickness of the metal
layer by a greater amount than if a fine metal powder had been used (meaning
the coarse metal powder has higher
deposition efficiency). In general, more passes will increase deposition time,
and weaken the adhesion strength of
the metal layer to the composite substrate.
[0081] If a coarse NiCrAlY powder is used with a 400 stainless steel mesh, 5
passes with ASP (current of 400
A, voltage of 60 V, Argon flow rate of 43.8 L/min, H2 flow rate of 6.57 L/min,
powder feed rate of 64 g/min, spray
distance of 13 cm, robot speed of 1 m/s) may result in the peeling off of the
mesh material from the composite
material layer.
[0082] If a coarse NiCrAlY powder is used, 3 passes with ASP (current of 400
A, voltage of 60 V, Argon flow rate
of 43.8 L/min, H2 flow rate of 6.57 L/min, powder feed rate of 64 g/min, spray
distance of 13 cm, robot speed of 1
m/s) may result in a metal layer of non-uniform thickness (the thickness may
become relatively uniform after at
least 4 passes).
[0083] In general, use of a fine powder, when compared to a coarse metal
powder, general has the following
effect on the above method or the resulting metal layer:
a. Lower porosity;
b. Higher oxidation;
c. Lower deposition efficiency (as more passes are needed to achieve the
same thickness);
d. Easier to control coating thickness (since each pass adds less overall
thickness);
e. Greater uniformity of thickness (especially when the thickness is low,
as shown in the experiment
section below); and
f. Less penetration into the mesh material (this may be because coarse powder
particles are
notably heavier than the fine powder particles, and consequently, when they
reach to the
composite substrate, they have more momentum and penetrate more into the mesh
material,
thereby resulting in higher adhesion strength).
[0084] As mentioned, one advantage of the method above is that, due to the
presence of the mesh layer (and
the roughened surface caused by the surface roughening step, including holes
created in the mesh material), the
resulting metal layer is anchored to the composite substrate, thereby
improving adhesion strength between the
metal layer and the mesh layer.
[0085] In addition, the presence of the mesh layer helps prevent damage to the
composite material layer during
the deposition step (including when ASP is used).
Date Recue/Date Received 2020-05-15
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[0086] It is also worth motioning that, using the above-defined method, the
metal layer will be deposited directly
on the composite substrate, without an intermediate layer.
Optional roughing step
[0087] As mentioned previously, before the metal layer is deposited onto the
mesh layer of the composite
substrate, it is preferable that the mesh layer be roughened (if it has not
already been roughened). This step is as
defined in the previous sections.
Optional addition of additional layers
[0088] In embodiments, as previously mentioned, additional layers may be added
to the metal layer. These
additional layers are as defined in the previous sections, and they can be
added using any known technique in the
art.
Advantages of the Invention
[0089] In developing the composite substrate and the metal-coated composite
substrate of the present invention,
the inventors discovered a composite substrate comprising a mesh layer that
makes for an effective substrate on
which to apply a metal coating, as the mesh material will protect the
underlying composite material layer during
the coating process and at the same time will act as an anchor to keep the
metal coating on the surface of the
composite substrate. Once coated with a metal layer, the composite substrate
makes for an effective electro-
thermal heating element, such as a de-icer or anti-icer.
[0090] In addition to the advantages previously discussed, the composite
substrate and the metal-coated
composite substrate of the present invention can present one or more of the
following advantages:
= The metal-coated composite substrate can be used as a heating element
without adding significant weight
to the composite material layer (only the weight of the mesh layer and metal
layers are added);
= The metal layer of the metal-coated composite substrate has high adhesion
strength with the composite
substrate, said adhesion strength being increased if the mesh layer has been
roughened before the metal
layer is deposited thereon.
= The mesh layer of the composite substrate has high adhesion strength with
the composite material layer.
= A metal layer of relatively uniform thickness on the metal-coated
composite substrate can provide for a
heating element with a surface temperature distribution of high uniformity.
= The metal layer on the metal-coated composite substrate may possess high
electric resistivity (due in part
to relatively high porosity and/or relatively high oxidation), which allows
the metal layer to more easily
generate heat, and allows the metal layer to achieve higher intensities with
lower current values.
= The metal layer on the metal-coated composite substrate may have high
resistance to galvanic corrosion,
and/or high mechanical strength.
Date Recue/Date Received 2020-05-15
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[0091] The methods of the present invention produce the above-defined
composite substrate and the metal-
coated composite substrate.
[0092] The method of producing the composite substrate of the present
invention results in a composite substrate
where the mesh layer has relatively high adhesion strength with the composite
material layer, and the method
allows for the mesh layer to be roughened (using, for example, abrasive grit
blasting) without damaging the
composite material layer.
[0093] In addition, the method of producing a metal-coated composite substrate
of the present invention may
allow for the deposition a metal layer that is of sufficiently uniform
thickness, with strong adhesion strength to the
composite substrate, with high electrical resistivity, high mechanical
strength, and/or resistance to galvanic
corrosion. This process may also allow for high deposition efficiency, without
damaging the composite material
layer during the deposition of the metal layer (using, for example, ASP
techniques) or during the roughing of the
mesh layer (using, for example, abrasive grit blasting).
Applications of the metal-coated composite substrate
[0094] As mentioned, the metal-coated composite substrate of the present
invention can be used as an electro-
thermal heating element, such as a de-icer or anti-icer. This applies to a
vast number of structures, such as in the
aerospace industry (e.g. aircrafts), and the energy industry (e.g. wind
turbines).
[0095] In addition, as previously mentioned, the methods of the present
invention can be used on both newly
constructed and previously existing structures as shown for example in Figure
1 (newly fabricated structure) and
Figure 2 (existing structure or part). For example, a composite substrate can
be manufactured from scratch and
then coated in metal according to the methods of the present invention (for
use on a newly constructed aircraft, for
example). Alternatively, an existing part of, for example, an aircraft can be
modified into a composite substrate
according to the present invention (using the method of producing a composite
substrate of the present invention),
and then a metal layer can be deposited onto said composite substrate (using
the method of producing a metal-
coated composite substrate of the present invention). The metal-coated
composite substrate can then be used as
an electrothermal heating element, for example by passing current through the
metal layer so as to generate heat
(as shown for example in Figure 3).
Definitions
[0096] The use of the terms "a" and "an" and "the" and similar referents in
the context of describing the invention
(especially in the context of the following claims) are to be construed to
cover both the singular and the plural,
unless otherwise indicated herein or clearly contradicted by context.
[0097] The terms "comprising", "having", "including", and "containing" are to
be construed as open-ended terms
(i.e., meaning "including, but not limited to") unless otherwise noted.
[0098] Recitation of ranges of values herein are merely intended to serve as a
shorthand method of referring
individually to each separate value falling within the range, unless otherwise
indicated herein, and each separate
Date Recue/Date Received 2020-05-15
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value is incorporated into the specification as if it were individually
recited herein. All subsets of values within the
ranges are also incorporated into the specification as if they were
individually recited herein.
[0099] All methods described herein can be performed in any suitable order
unless otherwise indicated herein
or otherwise clearly contradicted by context.
[00100] The use of any and all examples, or exemplary language (e.g., "such
as") provided herein, is intended
merely to better illuminate the invention and does not pose a limitation on
the scope of the invention unless
otherwise claimed.
[00101] No language in the specification should be construed as indicating any
non-claimed element as essential
to the practice of the invention.
[00102] Herein, the term "about" has its ordinary meaning. In embodiments, it
may mean plus or minus 10% or
plus or minus 5% of the numerical value qualified.
[00103] Unless otherwise defined, all technical and scientific terms used
herein have the same meaning as
commonly understood by one of ordinary skill in the art to which this
invention belongs.
[00104] Other objects, advantages and features of the present invention will
become more apparent upon reading
of the following non-restrictive description of specific embodiments thereof,
given by way of example only with
reference to the accompanying drawings.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENT
[00105] The present invention is illustrated in further details by the
following non-limiting examples.
[00106] Specifically, several experiments were performed, during which various
substrates were prepared and
coated with metal using a variety of parameters. The following section will
first detail the methodology used to
create the composite substrates that were tested, to create the metal-coated
composite substrates that were
tested, and to measure various properties thereof. The subsequent section will
detail the results of these
experiments.
EXPERIMENT METHODOLOGY
[00107] The experiment methodology consists of four steps including, 1)
fabrication and preparation of the
composite substrate (specifically GFRP composite substrates), 2) deposition of
a metal coating by using a plasma
spray technique, 3) determination of the coatings adhesion strength, 4)
electrical characterizations of the coated
samples and analyzing their performance as a heating element.
Part 1: GFRP composite substrate fabrication and preparation
[00108] In the first step, three 30 by 30 cm square plates were made using
GFRP (Cytec E773FR, 5 Garret
Mountain Plaza, Woodland Park, NJ 07424 USA) prepreg plies and stainless steel
mesh cloths. The GFRP
prepregs were taken out of the freezer and left at the room conditions for
about three hours. This allows the
temperature of prepreg to rise to room temperature and the viscosity is
reduced so that the prepregs can be cut
into smaller sheets easier. After that, the prepregs were cut into 30 by 30 cm
square sheets. For making a 4 mm
Date Recue/Date Received 2020-05-15
25
thick composite plate, 16 unidirectional GFRP plies (i.e. [016] composite)
were utilized. In order to protect the
composite fibers from the impact of high-velocity particles during preparation
and metal spraying (coating
deposition step), woven wire #200 and #400 stainless steel mesh cloths (type
316) were incorporated as a top
layer to the first and second plates, respectively. The properties of these
steel mesh cloths are listed in Table 1
below. After stacking and aligning the prepregs and steel mesh cloths, they
were placed on a tool and vacuum
bagged. The vacuum bag setup consisted of four primary items, including peel
ply and release film, breather and
bleeder cloth, vacuum bagging film, and a vacuum pump. After vacuum bagging,
the setup was transferred to an
autoclave for the curing process under the pressure and temperature of 74.5
kPa and 120 C, respectively. Figure
4 shows the fabricated composite plates.
[00109] Table 1: 200 and 400 stainless steel mesh cloths properties
Mesh count Nominal aperture Wire diameter Open area (c/o)
Weight kg/m2
200 75 pm 60 pm 34 0.28
400 38 pm 30 pm 31 0.16
[00110] Once the composite plates were fabricated, they were cut into smaller
samples using a diamond saw. In
the next step, the composite substrates were roughened and prepared for the
coating deposition process using
grit blasting. In the grit blasting process, the abrasive particles that are
sucked into a nozzle are accelerated toward
the substrate surface using a pressurized gas stream. More than 30 samples
were grit blasted to find an optimized
set of parameters for each type of composite substrate. These substrates
include the conventional composite
substrate (without addition of any metallic mesh), the plate fabricated by
addition of a 200 steel mesh cloth
(hereafter will be called the "200 mesh substrate"), and the plate fabricated
by addition of a 400 steel mesh cloth
(hereafter will be called the "400 mesh substrate"). The optimized grit
blasting parameters for each type of
composite substrate are shown in Table 2. It should also be mentioned that the
alumina grit used in the experiment
had an average diameter of about 80 pm. It should be noted that while the term
optimized is used both here and
throughout this experimental section to refer to parameters, other parameters
could be used.
[00111] Table 2: Optimized grit blasting parameters.
Grit blasting condition
substrate type Angle of grit impact
Pressure (psi) Time (s) Standoff distance (cm)
(degree)
Conventional
68 120 6 90
composite
200 mesh 76 150 6 90
Date Recue/Date Received 2020-05-15
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400 mesh 60 180 6 90
Part 2: Coating of Composite substrates
[00112] Once the
optimized parameters were found for grit blasting of the composite substrates,
Air Plasma
Spray technique (APS) was used for the deposition of a metallic coating layer
onto the composite substrates. Two
types of NiCrAlY powders with the fine (Amdry 9624, Oerlikon, size
distribution: -37 +11 pm) and coarse (Amdry
9625, Oerlikon. size distribution: -74 +45 pm) size distributions were
utilized for spraying and fabrication of a
heating element for the composite substrates. A 3MB plasma spray gun (Sulzer
Metco, Westbury, NY) was also
used to spray the NiCrAlY powders. Given that the composite substrates were
vulnerable to the high-temperature
gases and impact of high-temperature particles, they were cooled down using
two air amplifiers and two air blowers
to keep the substrates' surface temperature as low as possible during spraying
(below the composite curing
temperature). In the first step, four experiments were done for finding an
appropriate set of spray parameters for
the coating of the composite samples using fine NiCrAlY powder (see Table 3
below). It was found that coatings
with high quality and adhesion could be generated using Exp 4 spray
parameters. It was also found that acceptable
coatings could be deposited by using Exp 4 parameters and the coarse NiCrAlY
powder. Given that in the case of
using coarse NiCrAlY powder, the coating thickness changed significantly with
the number of passes, the
composites were coated with three different numbers of passes (Exp 5-7 in
Table 3). Upon the completion of the
coating process, a metallographic technique was used for analyzing the
microstructure of the coated samples
under a microscope. After finding the proper spray parameters, larger
composite samples (2.3-by-10 cm) were
coated for the mechanical and electrical characterizations. Figure 5 shows the
image of a grit-blasted 200 mesh
sample after coating by the coarse powder and using the Exp 6 spray
parameters.
[00113] Table 3: The plasma spray parameters used for the coating of composite
substrates
Primary Secondary Powder Spray Robot Number
Current Voltage gas, Ar gas, H2 feed rate
distance speed of
(A) (V) (I/min) (I/min) (g/min) (cm) (m/s) passes
First Series (fine NiCrAlY powder)
Exp 1 1
500 60 43.8 6.57 64 13 10
(Ref)
Exp 2 500 60 43.8 6.57 32 13 1 20
Exp 3 500 60 43.8 6.57 64 15 1 10
Exp 4 400 60 43.8 6.57 64 13 1 10
Second Series (coarse NiCrAlY powder)
Date Recue/Date Received 2020-05-15
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Exp 5 400 60 43.8 6.57 64 13 1 3
Exp 6 400 60 43.8 6.57 64 13 1 4
Exp 7 400 60 43.8 6.57 64 13 1 5
Part 3: Adhesion Strength
[00114] In this step, a flatwise tensile test was performed for measuring the
adhesion strength (bond strength)
of the coated samples. For this purpose, first, a two-component adhesive
(Henkel Loctite Hysol EA 9392 AFRO
Epoxy Adhesive Gray, LOCTITE, Henkel Canada Corporation, Canada) including
epoxy and hardener were mixed
together with a weight ratio by weight of 100: 32. On completion of the
mixing, a thin and even layer of the mixture
was applied on both sides of the 2.5 by 2.5 cm coated samples. Following this,
the samples were sandwiched
between two stainless steel blocks and placed in an oven at a temperature of
85 C and for about 90 minutes for
curing the adhesive. Once the curing process was completed, the blocks were
connected to two Wyoming flatwise
tensile test fixtures by using two pins. The fixtures were then placed in a
flatwise tensile machine (with a
displacement rate of 0.50 mm/min) for applying tension and measuring the
adhesion strength of the coatings. The
samples then were analyzed for detecting the failure type.
Part 4: Electrical characterization of the coated samples
[00115] Given that the amount of heat generated by a coated heating element
(de-icing element) for a given
current depends directly on the coating electrical resistance, the electrical
properties of the coating were
determined. For this purpose, the four-point electrical probe technique was
used for determining the electrical
properties of the specimens. This technique is very useful for eliminating the
wire and contact resistances that may
cause an error in calculating the resistance of the sample. A schematic view
of this method is shown in Figure 6.
As can be seen in this figure, for doing the four-point probe test, four wires
were attached to the samples top face.
A constant current was applied to the sample through probes 1 and 4 connected
to a power supply. In addition, an
ammeter was installed in series with the circuit and between the power supply
and probe 4 for increasing the
accuracy of the current measurement. A voltmeter was connected to the sample
using probes 2 and 3 for
measuring the voltage drop between these two spots. It should also be noted,
given that the voltmeter is parallel
to the circuit and has a very high resistance, no current passes through the
voltmeter, so it has no impact on the
amount of current registered on the ammeter.
[00116] Different electrical currents (6, 9, and 12 A) were applied to the
samples, and the resulted voltage drop
between spots 2 and 3 was measured using a voltmeter at the same time. The
electrical resistance Rand resistivity
p of the coatings were then calculated as follows:
V ,AV
R = = (1)
Date Recue/Date Received 2020-05-15
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¨Al = R¨bId
p = R
(2)
[00117] Sheet
resistance is another electrical term used more for electrical
characterization of the relatively
thin coatings and paints. By referring to Equation 1, the sheet resistance can
be calculated as follows:
1 p1 1
R = p A¨ = p¨bd= ¨d¨b= Rs ¨b (3)
Where (4)
Rs =
[00118] Rs is the sheet resistance. The sheet resistance is the resistivity of
a specimen divided by its thickness
and its unit is ohme Q. For analyzing the performance of the coatings in
generating heat and acting as a heating
element, the generated power per unit area (intensity) in each coated sample
for a given current was calculated
by using the following equation:
Intensity = ¨AP = l RI2
¨A (5)
in which As is the surface area.
EXPERIMENT RESULTS AND DISCUSSION
Part 1: Composite substrates preparation
[00119] As mentioned, three types of composite substrates were prepared for
the deposition of the NiCrAlY
coating, which are: conventional composite substrate, 200 mesh substrate, and
400 mesh substrate. Before grit
blasting and preparing the substrates for the coating deposition process, the
200 and 400 mesh substrates were
characterized and their cross-sections were examined under an optical
microscope. Figures 7 (a) and (b) shows
the low and high magnification microscopic images of 200 and 400 mesh
substrates cross-section after fabrication,
respectively. In the case of 200 mesh substrate (Figure 7(a)), it can be seen
that the epoxy penetrated perfectly
through the steel mesh wires and formed a uniform and thin layer on top of the
mesh. In the case of 400 mesh
substrate (Figure 7(b)), the overall resin penetration through the steel mesh
is relatively good. However, by going
to a higher magnification, it can be seen that the resin penetration in some
locations is insufficient. This is possibly
because the steel mesh used in the 400 mesh substrate is very fine, and
consequently a perfect resin penetration
through the steel mesh is very difficult and demands to apply high pressures
to the composite plates during the
curing process. Therefore, it can be concluded that the steel mesh in the 200
mesh substrate may generally have
higher adhesion strength to the underlying composite material layer.
[00120] After examination of the cross-section of the composite substrates,
the samples were grit-blasted under
different grit blasting parameters. Figure 8 depicts the cross-section of a
conventional composite substrate without
any metal mesh after grit blasting. From this image, it is obvious that grit
blasting induced significant damage to
Date Recue/Date Received 2020-05-15
29
the fibres due to the impact of high-velocity abrasive particles. Presence of
the metal mesh can protect the fibres
and at the same time act as an anchor to keep the coating on the surface.
Proper preparation of the polymeric
samples prior to the coating deposition may affect the fabrication of a
uniform coating with high-quality.
[00121] As mentioned earlier, more than 30 composite substrates (200 and 400
mesh substrates) were grit-
blasted to obtain an optimized set of grit blasting parameter for each type of
substrate. Figure 9 shows the confocal
images of the top surface of three 200 mesh substrates grit-blasted with
different parameters. In the first case, in
which the substrate was grit-blasted with an air pressure of 76 psi for 200 s,
it can be seen that some steel wires
were removed or damaged. In the second case, the substrate was grit-blasted
with a pressure of 50 psi for 90 s.
In this sample, unlike the previous case, no damage is induced to the steel
wires. However, in this case, a high
percentage of the wires is still covered with epoxy, and this may have a
negative impact on coating adhesion and
deposition efficiency in the next steps (see below) due to the fact that the
more steel wires there are on the
substrate surface, the better the coating adhesion may be. Finally, the last
case shows a 200 mesh substrate grit-
blasted with the optimized parameters (P= 76 psi and t= 150 s). In this
sample, the steel wires are in good condition
and comprise a high percentage of the composite surface, while they also have
a good anchorage and bonding
with the composite part. In fact, using these optimized grit blasting
parameters resulted in removing about 50% of
the epoxy exist on top of the steel wires. Figure 10 illustrates the grit-
blasted 400 mesh substrates. From this figure,
it is clear that the optimized case was achieved (due to the same reasons as
for grit blasting the 200 mesh
substrates) by grit blasting the 400 mesh substrate with an air pressure of 66
psi for 180s.
[00122] Globally, by comparing Figures 9 and Figure 10, it can be found that
optimizing the grit blasting
parameters can improve the roughening of the substrate surface. The 200 mesh
substrates are less sensitive and
vulnerable to the grit blasting parameters as their cloth steel wires are
thicker and more resistant to the impact of
high-velocity particles and better results were obtained when compared to the
400 mesh substrates. Furthermore,
as the metallic mesh holes' dimensions were smaller than the grit blasting
sand diameter, the sand likely could not
penetrate to the composite part of the substrates and break the fibers during
grit blasting. By measuring the surface
roughness, it was also found that the 400 mesh substrate grit-blasted with the
optimized parameters has a surface
roughness of about 7 pm, while this value for the 200 mesh grit-blasted with
the optimized parameters is about 11
pm (about 50% higher compared to the grit-blasted 400 mesh substrate). This
might be due to the relatively large
voids existing on the 200 mesh substrate surface. So, it is expected that
using this kind of substrate may result in
a better coating deposition and adhesion during spraying.
Part 2: Coating of the composite substrates
[00123] Four experiments (see Table 3 above) were performed to find an
appropriate set of spray parameters for
depositing a NiCrAlY coating layer onto composite substrates. In this series
of experiments, the NiCrAlY powder
with fine size distribution (-37 +11 pm) was used as the coating material. In
experiment 1, samples were coated
using the reference parameters. As shown in Figure 11, in this experiment, all
the composite samples were burnt,
and in the cases of 200 and 400 mesh substrates, in addition to the burning,
the steel cloth and coating were
peeled off from the composite part of the substrate. These results might be
explained by the fact that the
Date Recue/Date Received 2020-05-15
30
temperature of the substrate during coating deposition (about 200 C) exceeded
the material limits. Consequently,
the bonding between the steel wire and the composite part got loose and the
steel mesh cloth started debonding
from the substrate.
[00124] In experiment 2, in which the powder feed rate was decreased from 64
to 30 g/min (compared to
experiment 1), the samples were not burnt. However, as shown in Figure 12, the
coating deposition efficiency was
low. The maximum surface temperature of the substrates in this experiment was
about 110 C. In experiment 3,
in which the standoff distance was increased from 13 cm to 15 cm (compared to
experiment 2), the deposition was
also low. In addition, partial burnings were observed in all the composite
samples. The maximum surface
temperature of the substrates during spraying was about 165 C.
[00125] In experiment 4, the plasma current was reduced from 500 A to 400 A.
Consequently, the plasma input
power decreased about 25% compared to the previous experiments. The maximum
surface temperature of the
substrates during spraying was about 105 C. Figure 13 depicts the cross-
section of the samples coated using
experiment 4 spray parameters with low magnification. It can be seen that in
the case of the conventional composite
substrate (Figure 13a), the coating deposition and adhesion is very low.
Furthermore, it is clear that the composite
surface is non-uniform, and a lot of composite fibers were removed from the
top of the substrate due to the grit
blasting done before the spraying process. As shown in Figure 13b, in the case
of not grit-blasted 200 mesh
substrate, the coating deposition is better than the previous, but still
limited and non-uniform. In a not grit-blasted
200 mesh substrate, the steel wires are covered with a thin epoxy layer. So,
when the molten NiCrAlY particles
(during spraying) reach to the substrate, they face with an epoxy layer
instead of metallic wires. That is likely why
the coating deposition, in this case, is limited. In addition, since this
sample was not grit-blasted before the coating
deposition process, there was no rough surface for the molten particles to
lock into and fully adhere. From Figure
13c and d, it is apparent that grit blasting the 200 and 400 mesh substrates
have made a considerable improvement
in the coating adhesion and deposition efficiency. Indeed, in these
substrates, the steel mesh protected the
composite part, especially the fibers, from the impact of high-velocity
particles during grit blasting and spraying. In
addition, as the steel wires comprised a high percentage of the surface of 200
and 400 mesh substrates, the
NiCrAlY coating was deposited with high uniformity and efficiency. In
addition, the holes created by grit blasting
between the steel wires may have an influence on improving the anchorage of
the molten particles to the substrate
surface and consequently on improving the coating adhesion.
[00126] Figure 14 shows the coated 200 and 400 mesh substrates with higher
magnification, and a coated
stainless steel block. It is clear that in these three samples, the coatings
are very similar to each other from
uniformity, thickness, and quality points of view. This shows that the
addition of steel mesh cloths to the composite
substrates has improved the coating deposition efficiency up to a grit-blasted
stainless steel block. The average
coating thickness in this experiment was about 94 2.3 pm.
[00127] In the second phase of experiments (experiments 5-7), composite
substrates were coated using the
coarse NiCrAlY powder with a size distribution of -74+45 pm, which allowed for
a comparison to be made between
the coatings sprayed using the coarse powder and those sprayed using the fine
powder. This comparison mainly
Date Recue/Date Received 2020-05-15
31
includes analyzing the coatings microstructure, thickness, amount of
oxidation, and electrical resistivity to
determine which type of coating might be more proper as a heating element. It
was found that experiment 4 spray
parameters are also suitable and proper for the deposition of coating using
coarse NiCrAlY powder. The coating
thickness was changing significantly with the number of passes and the
deposition efficiency was higher. The
composites were coated with the different number of passes (i.e. 3, 4, and 5
passes).
[00128] In experiment 5, samples were coated in three passes. As shown in
Figure 15, in both the grit-blasted
200 and 400 mesh substrates, the coating is not uniform. The generated
coatings had an average thickness of
39.0 3.1 pm. The maximum surface temperature of the substrates during spraying
was about 109 C.
[00129] In experiment 6, in which the composite samples were coated in 4
passes, the coatings had a relatively
uniform thickness (see Figure 16). The average thickness of the deposited
coatings was about 83.5 4.2 pm. By
comparing Figure 14 and Figure 16, it can be found that the NiCrAlY coating
deposited using coarse NiCrAlY
powder has a higher porosity and lower degree of oxidation in comparison to
the one deposited using fine NiCrAlY
powder. The higher porosity could be attributed to the fact that in the plasma
plume, coarse particles have relatively
lower melting efficiencies and lower speed than fine particles which result in
larger amounts of unmolten particles
and the formation of big pores between coating splats. In addition, the total
surface area of the fine particles (sum
of the surface area of all particles) sprayed in a period of time is
considerably greater than that of the coarse
particles which contributes to more heat absorption, and consequently more
oxidation when the fine powder is
used for the coating deposition. The maximum surface temperature of the
substrates in this experiment also was
about 118 C.
[00130] Finally, in experiment 7, the coatings were sprayed onto the composite
substrates in 5 passes. As shown
in Figure 17, the coating was deposited on the top of the grit-blasted 200
mesh substrate utterly and without
inducing any damage to the composite part. However, when the grit-blasted 400
mesh was used as a substrate,
the coated steel mesh cloth started peeling off during the fifth pass. This
peeling off was likely due to the imperfect
bonding of the steel mesh cloth to the composite part, the weak and thin steel
wires, as well as the residual stresses
induced to the substrate by increasing the number of passes and coating
thickness. The coatings deposited in this
experiment had an average thickness of 96 4.0 pm. The substrates had a maximum
surface temperature of about
135 C.
[00131] Overall, the results of these seven experiments show that an
appropriate and uniform NiCrAlY coating
layer could be deposited onto the grit-blasted 200 and 400 mesh substrates by
using both fine and coarse NiCrAlY
powders. It can also be seen that using the powder with the fine size
distribution resulted in the formation of a
coating with higher uniformity as the powder particles were significantly
smaller compared to those of the coarse
powder. The image analysis results also show that in the coatings generated
using fine powder, the porosity is
very low (0.9 0.1 %), and the oxidation is relatively high (31.6 1.6%). On
the contrary, in the coating generated
by the coarse powder, the porosity is relatively high (6.4 1.2 %), and the
oxidation is relatively low (11.8 1.4
%). It also seems that utilizing the coarse powder contributes to a better
deposition efficiency as a 100 pm NiCrAlY
coating layer can be fabricated in 5 passes using the coarse powder and in 10
passes using the fine powder while
Date Recue/Date Received 2020-05-15
32
the powder feed rate in both cases is 65 g/min. However, it should be noted
that controlling the coating thickness
in the case of using fine powder tends to be considerably better and easier.
Another interesting observation is that
the coating tends to penetrate more into the mesh cloth and substrate when it
is sprayed using the coarse powder.
This might be explained by the fact that the coarse powder particles are
notably heavier than the fine powder
particles, and consequently, when they reach the substrate, they have more
momentum and penetrate more into
the steel mesh cloth. It should also be noted that in all cases, the coatings
did not reach and damage the composite
fibers.
Part 3: Adhesion strength
[00132] In order to quantify the adhesion between the substrate and coating, a
flatwise tensile test (defined above)
was performed. The bonding strength results of the NiCrAlY coatings deposited
onto the composite substrate are
depicted in Figure 18. In this figure, the code used to identify the samples
consists of three parts. The first part
specifies the type of coating material and F stands for the fine powder and C
stands for the coarse powder. The
second part stands for the number of passes in which the coating was deposited
in and the third part specifies the
type of composite substrate, 200 stands for the 200 mesh substrate and 400
stands for 400 mesh substrate. The
adhesion strength test was repeated 3 times for each coated sample. As shown
in Figure 18, samples C-4-200
and F-10-200 have the highest coating adhesion strength. Another interesting
observation is that globally the
samples in which 200 mesh composites were used as the substrate (except C-5-
200) have a higher adhesion
strength compared to the samples in which 400 mesh composites were used as the
substrate. In all coated 400
mesh substrates (C-3-400 and C-4-400), the failure occurred at the interface
of the steel mesh cloth and the
composite part (see Figure 19). This is likely due to the imperfect bonding of
the 400 mesh cloth to the composite
part. The maximum adhesion strength in the case of a coated 400 mesh substrate
is around 15 MPa. On the other
hand, as shown in Figure 19, the failure mode in the cases in which 200 mesh
composites were used as the
substrate, is a combination of coating failure and mesh cloth failure. The
lowest bonding strength was achieved for
sample C-5-200. This observed decrease in the adhesion strength could be
attributed to the significant stresses
that were induced to the substrate due to increasing the number of passes and
coating thickness as well as being
in the exposure of hot gas temperatures for a longer amount of time. The
adhesion strength values obtained for
samples C-4-200 and F-10-200 are about 50% higher than the adhesion strength
values reported for the coated
composites in the literature.
Part 4: Electrical characterization
[00133] The coated samples were characterized electrically using the four-
point probe method (defined above).
Currents of 6, 9, 12 A were applied to the coated samples and the resulted
voltage was measured. The relationship
between the applied currents through the coating and the corresponding voltage
for the coated samples with the
dimensions of 2.3-by-10 cm is shown in Figure 20. As expected, in all cases,
the voltage has a linear relationship
with the current. This shows that all the coated samples obey Ohm's law. Given
that R = = ¨, the V-I curves'
slope represents the electrical resistance of the coatings. So, the electrical
resistance of samples F-10-200, C-5-
Date Recue/Date Received 2020-05-15
33
200, C-4-200, and C-3-200 are 0.091, 0.104, 0.116, and 0.263 Q, respectively.
The resistance of the coated
samples was also measured at different temperatures (25 to 150 C). It was
found that in that range of temperature,
in all the cases, the resistance of the NiCrAlY coating is almost constant and
independent of the coating surface
temperature. This is one of the advantages of NiCrAlY over other materials
used for the fabrication of heating
element coatings (e.g. NiCr, FeCrAI). From Figure 20, it is apparent that
sample C-3-200 has the highest resistance
value. In fact, as R = p ¨Al = p d , the resistance is directly proportional
to the electrical resistivity and length and
is inversely proportional to the cross-section area. By increasing the number
of passes and consequently the
coating thickness, the resistance tends to decrease. In addition, by comparing
samples C-5-200 and F-10-200 it
can be seen that the resistance of the former is a little bit higher, while in
both cases, the coating thickness is
approximately the same. This is due to the fact that the electrical
resistivity of the coatings generated by the coarse
powder is about 12% higher than that of the coatings generated by the fine
powder (see Table 4 below). By having
the resistance of the coatings, the resistivity could be calculated.
Resistivity is an intrinsic property that unlike
resistance does not depend on the shape and dimensions of the material. So,
the resistivity value of two coatings
sprayed with the same spray parameters but with a different number of passes
should be similar and close to each
other. However, as the spray parameter and powder size have a direct impact on
the percentage of coating
oxidation and porosity, changing them may slightly result in different
resistivity values. In addition, since the
coatings are always associated with porosity and oxidation, their intrinsic
properties like electrical resistivity are
usually different from the bulk and pure materials. As mentioned earlier, the
image analysis showed that the
coatings generated using fine powder have a porosity of 0.9 0.1 % and an
oxidation of 31.6 1.6 %, and the
coatings generated using coarse powder have a porosity of 6.4 1.2 % and an
oxidation of 11.8 1.4 %. By
comparing the resistivity values of the coatings, it seems that the porosity
had a more important role and impact,
compared to the oxidation, in increasing the coating resistivity value.
[00134] Sheet resistance, which is an electrical term used more for
characterizing thin coatings, was calculated
using Rs = = R Lt. The sheet resistance values for different types of coatings
are shown in Table 4 below. One
advantage of sheet resistance over electrical resistance is its independence
from the size which makes a
comparison between different samples easier. It also shows the capability of a
sample in generating heat when a
given current is applied to it. The sheet resistance of sample C-3-200 (about
0.058 Q/square) is noticeably higher
than that of the other coated samples due to its lower thickness. This means
that this type of coating should
generate more power and heat compared to the other coated samples for a given
current. The sheet resistance
values of the other coated samples are relatively close to each other as there
is not a very big difference between
their thicknesses and resistivity values.
Table 4: Electrical properties of the coated samples.
Average sheet resistance
Sample type Average p (pQ.m)
(Q/square)
Date Recue/Date Received 2020-05-15
34
C-3-200 2.264 0.179 0.0580 0.0100
C-4-200 2. 170 0. 109 0.0268 0.0021
C-5-200 2.295 0.095 0.0239 0.0020
F-10-200 1.993 0.048 0.0212 0.0020
Part 5: Performance of the coated samples as a heating element
[00135] Once the samples were characterized electrically, their performance in
generating power and acting as a
heating element was tested. For this purpose, the generated intensity (power
per unit area) of the coated composite
samples for a given current was calculated using Intensity = ¨AP = -RI
equation. The amount of generated
intensity in the coated samples for 6, 9, and 12 A currents is presented in
Figure 21. The intensity goes up
significantly by increasing the current as it is directly proportional to the
square of the current value. It is apparent
that sample C-3-200 has the highest capability in generating heat due to its
considerably higher resistance value
compared to the other samples. Based on the literature, the amount of
intensity needed to be provided by the
heating elements for de-icing purposes is in the range of 2.1-3.6 kW/m2.
[00136] The infrared camera pictures (see Figure 22) show that in cases in
which the coating thickness is not
uniform, like sample C-3-200, the surface temperature distribution of the
coating (while it is connected to a power
source) is also non-uniform, while in the other cases (samples F-10-200, C-4-
200, and C-5-200) in which the
coating is uniform, the surface temperature distribution also has a high
uniformity. In fact, when a coating is not
uniform, the electrical resistance changes along the coating and this
consequently tends to result in the generation
of different amounts of power along the surface coating. That is likely why
such a coating does not have a uniform
surface temperature. Based on several factors, like the intended application
of heating element, where it is intended
to be used, the amount of power needed, the importance of uniformity, and
other limitations, each of these heating
element coatings might be useful.
CONCLUSION
[00137] In these experiments, a method for the fabrication of a NiCrAlY
coating layer on polymer-based composite
materials by using a plasma spray technique is tested. Three types of
composite substrates were made by using
glass fibre reinforced prepreg plies and stainless steel mesh cloths, which
were: 1) a conventional composite
substrate, 2) a 200 mesh substrate, which was made by incorporating an extra
200 stainless steel mesh cloth on
top of the prepregs, and 3) a 400 mesh substrate which was made by
incorporating an extra 400 stainless steel
mesh cloth on top of the prepregs. After preparing the composite substrates by
grit blasting, the samples were
coated by fine and coarse NiCrAlY powders. The microscopic images of the
coated sample cross-sections revealed
that the deposition of a metallic coating onto conventional composites is very
limited. In this case, the grit blasting
also resulted in breaking and damaging the composite fibers significantly.
However, in the cases of 200 and 400
mesh substrates, it was observed that a uniform NiCrAlY coating with high
deposition efficiency and uniformity
Date Recue/Date Received 2020-05-15
35
could be deposited by using a proper set of spray parameters. Indeed, the
incorporation of the stainless steel mesh
cloths to the composite structure not only improved the coating adhesion and
deposition efficiency significantly but
also played the role of armor for the composite part and protected the
composite fibers from the impact of high-
velocity particles during grit blasting and spraying. It was also observed
that using the fine NiCrAlY powder resulted
in the generation of coatings with very high uniformity. Also, the coatings
that were deposited in 4 and 5 passes
using the coarse powder had adequate uniformity. However, the controllability
in the case of using coarse powder
was relatively low as the coating thickness was changing significantly with
the number of passes. The deposition
efficiency of the coarse powder also was higher than the fine powder. The
results of the coating adhesion strength
showed that the coating bonding strength in the cases in which the 200 mesh
composite was used as the substrate
is very high. The adhesion strength values obtained for samples C-4-200 and F-
10-200 (about 22 MPa) were about
50% higher than the adhesion strength values reported for the coated
composites in the literature.
[00138] The
results of the electrical characterization of the coated samples also
indicated that using NiCrAlY
powder with the coarse size distribution (compared to the fine powder) tends
to result in the formation of coatings
with higher resistivity value. After checking the performance of the coated
samples as a heating element, it was
found that all the coated samples have the capability of generating intensity
more than the amount of intensity
required for de-icing applications. Sample C-3-200 had the highest capability
in generating power for a given
current; however, in this case, unlike other samples (F-10-200, C-4-200, and C-
5-200), the surface temperature
distribution was non-uniform. Based on several factors, like the intended
application of heating element, where it
is intended to be used, the amount of power needed, the importance of
uniformity, and other limitations, each of
these heating element coatings might be useful. It is worth noting that the
200 steel mesh cloth used in this study
just adds 0.28 kg/m2 to the weight of the substrate, while the equipment used
in conventional de-icing systems
(like bleed air de-icing systems) adds hundreds of pounds of weight to the
aircraft.
[00139] The scope of the claims should not be limited by the preferred
embodiments set forth in the examples,
but should be given the broadest interpretation consistent with the
description as a whole.
Date Recue/Date Received 2020-05-15
36
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