Note: Descriptions are shown in the official language in which they were submitted.
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'l'H ~ MAI, BARRIER COATING AND METHOD
OF DEPOSll~G 'l'H~ SA~ E ON
COMBUSTION CHAMBER COMPONENT SURFACES
Technical Field
This invention relates generally to thermal
barrier coatingfi applied to the surfaces of metallic
componentfi in internal combustion engines. In
particular, and more specifically, the invention relates
to ceramic-refractory coatings and a process of applying
the same to the surfaces of combustion chamber
components in compression ignition internal combustion
engines.
BackPround Art
Heat-insulating structures and heat-insulating
coatinqs, i.e. thermal barrier coatings have been
employed by those skilled in the art to enhance the
thermal efficiency of internal combustion engines by
permitting more complete fuel burning at higher
temperatures. Typically, such heat-insulating coatings
have been applied to all of the chamber surfaces,
includinq the cylinder wall and head and piston
combustion face to prevent heat loss.
Heat-insulating structures and heat-insulating
coatings have also been used in automobile exhaust
systems to maintain high exhaust temperatures required
by thermal reactors and catalytic converters and to
impede the emission of unburned hydrocarbons emitted
into the atmosphere as an undesirable component of
exhaust gas.
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In previous attempts to increase thermal
efficiency, heat-in6ulating structures and heat-
lnuul~tlng coatlng~ such as ceramic plate6 and ceramic
coatlngs, reupectlvely, have been applied to component
~urfaces. Significantly, such ceramic coatings function
not only as heat insulation barriers but also exhibit
advantageous physical characteri~tics such as providing
a hard, corrosive resi6tant, and abrasive resistant
surface.
Typical of ceramic materials commercially
available include a cerium-yttrium zirconium oxide
material as described in U.S. Patent No. 4,599,270,
available the Perkin-Elmer Corporation.
The above ceramic materials were developed
princlpally for application to high speed turbine
blades, such as used in commercial aircraft, turbo jet
engine6. Typically, these blades are made of nickel-
based superalloy, high strength steel materials and the
environment is one in which the blades, thus the ceramic
linlng on the blades, is ~ub~ected to high temperatures
at relatively constant, non-cyclical, compressive loads.
Prior art literature describing the use of
ceramic materials for these applications and techniques
for applying the ceramic lining are shown in more detail
in ~.S. Patent Nos. 4,273,824; 4,332,618; 4,335,190;
4,880,614; and 4,916,022.
The need or demand for such a heat insulating
barrier in internal combustion engines, and particularly
two and four cycle compression-ignition (diesel)
engines, has only recently come to be realized. Recent
engine designs, and the modification of pre-existing
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engine designs, has included increasing the power output
demands for a cubic inch di~placement of the engine's
power capaclty. Such de~ign6 have resulted in higher
compression ratios and exhaust gas temperatures. Not
only i6 it important to keep the exhaust gas
temperatures from reaching the cylinder head and related
components, thus reducing the cooling requirements and
other engine design requirements, the heat of the
exhaust gas is being used to increase the engine
efficiency by recirculating it through the intake air
ports.
However, experience has shown that the ceramic
coatings and techniques for application to apparatus
such as gas turbine engine blades, previously
referenced, is not ideal for application to the surfaces
of combu6tion chamber components in compression-ignition
internal combustion engines, where (i) the substrate
materials including the cylinder head and piston may be
cast iron, (ii) the materials of the related components
such as the exhaust valves may be aluminum alloyed high
temperature steel or metallic based alloy, and (iii) the
temperatures in the combustion chamber and at the
combustion chamber surfaces are extremely high.
Prevlously known ccramlc coatings and
technlques ~or depo~lting the same are even less ideal
for 2-cycle compression-ignition internal combustion
engines such as applicant's Series 149 engine which
utilizes a pot-type cast iron cylinder head. In
applicants' Series 149 engine design, the temperatures
in the combustion chamber are even greater than in
conventional internal combustion engines, since every
stroke of the piston i5 a combustion stroke. For
example, temperatllres in the combustion chamber may vary
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between 150 to 1400. Similarly, temperatures at the
combustion chamber surfaces cyclically range from about
150 when being freshly charged with intake air to about
1500 at combustion. All of these factors contri~ute to
the requirement for new materials and techniques in
accordance with the present invention.
Prior disclosures include those shown in U.S.
Patent Nos. 3,9~1,890, 3,976,809 and 3,911,891 for
coating pi~ton heads and 4, 077, 637 for coating piston
rings, as well as 4,254,621 for ceramically coating any
of the combustion chamber surfaces including the
cylinder head. However, none of these is considered to
serve the purposes of the present invention in providing
an extremely cost effective and efficient dual layer
ceramic lining and application technique for lining the
combustion chamber 6urfaces of a compression-ignition
internal combustion engine expanded to the above-
mentioned operating condltions.
Summary Of The Invention
It is an object of the present invention to
provide a protective coating for application to the
surfaces of combustion chamber components exposed to
cycllcal temperatures and compression loads.
It is another object of the invention to
provide a thermal barrier coating comprised in part of
a ceramic refractory material for application to the
internal 6urfaces of combustion chamber components,
including the cylinder head, exhaust valves and piston
heads. A6 more fully set forth herein, the thermal
barrier coatlng 1~ capable of provlding ~ood adherence
to the material~ and heat insulation properties in an
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environment where the temperatures cyclically range from
150F to 1400F in the compression chamber, 150 to
1500F at the combustion chamber surfaces and where the
compressive loads on the coating may be as high as 2500
pounds per square inch.
It ifi a further object of the invention to
provide a thermal barrier coating which is economical,
and readily adaptable to being deposited on a metal
substrate by means of plasma spray vapor deposition.
Yet another object of the invention is to
provide a method of depositing a thermal barrier coating
on the surfaces of combustion chamber components,
including the cylinder heads, exhaust valves and piston
heads, which is economical and reliable.
A more specific object of the present
invention is to provide a dual layer thermal barrier
coating for the surfaces of the combustion chamber
components in a compression ignition internal combustion
engine. In accordance with the present invention, the
thermal barrier coating comprises a metallic layer
deposited on the component surface and a ceramic layer
deposited on the metallic layer to impede the flow of
heat therethrough. The metallic layer creates a
mechanical bond between the component surface and the
ceramic layer, allows for a smooth transition between
differing physical properties of the component and the
ceramic layer and serves as a corrosion barrier by
protecting the component from combustion gases and
contaminants.
It is yet another specific ob;ect of the
pre~ent invention to provide a method of depositing a
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dual layer thermal barrier coating on the surfaces of
combustion chamber components in a compression-ignition
internal combustion engine. In accordance with the
present invention, the component surface should first be
grit bla6ted to eliminate oxides and roughen the surface
to increase the available surface area for deposition.
A metallic layer is then deposited on the component
surface to protect the component from corrosion caused
by combustion gases and contaminants. Finally, a porous
ceramic layer is deposited on the metallic layer to
impede the flow of heat therethrough.
These and other objects and advantages of the
present invention will be more obvious and apparent with
reference to the drawings and detailed description of
the invention which follows.
~rief Description Of The Drawings
FIGURE 1 is an enlarged cross-sectional view
of a pi6ton dome illustrating the metallic and ceramic
layer6 of the thermal barrier coating of the present
invention applied to the face;
FIGURE 2 i~ a plan view of a Series 149 pot-
type cylinder head utilized in 2-cycle compression-
ignition internal combustion engines manufactured by
applicant and shown with the thermal barrier coating of
the present invention applied thereto; and
FIGURE 3 is a block diagram view of the method
~teps of the pre6ent invention.
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Best Mode For Carryinp Out The Invention
Re~errlng to Figures 1 and 2, the present
invention is directed to a dual-layer protective coating
and a method of applying the coating to the surfaces of
component6 which form the chambers of internal
combustion engines. In Figure 1, there is shown a
piston dome generally designated by reference numeral lo
as u6ed by applicant in its hiqh output, Series 149
compression ignition internal combustion engines.
Figure 2 shows the protective coatinq of the preset
invention as applied to applicant's Series 149 pot-type
cylinder head. ~oth components shown in Figures l and
2 are constructed of cast iron for conventional
~pecifications.
Aithough the use of thermal barrier coatings
is known ~n the art, particularly the aerospace
i~dustry, previous desiqns and methods of ap~lication
have proved inefficient and in many cases inoperable.
In the case of compre6fiion-ignition internal combustion
engines, and particularly 2-cycle compression-ignition
engines, 5pallations i.e., the flaking of ceramic
materials due to poor adhesion caused by thermal fatigue
is recognized as the primary failure mode observed in
the applicakion of ceramic coatings to component
surfaces.
In an effort to overcome the inefficiency and
inoperability of known protective linings, applicant has
developed a dual layer protective lining and method of
applying the ~ame to the surfaces of combustion chamber
components ln compre~ion-ignition internal combustion
englneB a8 more fully described herein.
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Still referring to Figure 1, there is shown a
thin metallic layer 14 deposited on the component
curface 12 to protect the component from corrosion
cau~ed by combustion gases and contaminants. In the
case of piston domes, as in ~igure 1, it is recognized
that the component surface must initially be machined
back (~hown generally by reference numeral 11) to the
specified coating thickness to retain the proper
compression ratio. Metallic layer 14 is preferably
deposited to a thickness between 0.003 - 0.006 inches
and is comprised of a MCrAlY material selected from the
group consisting of nickel base alloy (NiCrAlY), cobalt
ba~ed alloy (CoCrAlY), nickel cobalt base alloy
(NiCoCrAlY), and iron base alloy (FeCrAlY).
Still referring to Figure 1, there is shown a
porous ceramic layer 16 deposited on the metallic layer
14. Ceramic layer 16 is preferably deposited to a
thicknes~ between 0.010 - 0.015 inches and i6 comprised
of material having between 10-15 percent volume
porosity. More particularly, ceramic layer 16 may be
comprls~d of yttrium partlally stabllized zirconia or
ceria-yttrium partially stabilized zirconia. In the
former case, applicant has found it preferable that the
ceramic layer be comprised of eight percent yttrium
partially 6tabilized zirconia.
Metallic layer 14 referenced above in the dual
layer thermal barrier coating of the present invention
is recognized as creating a mechanical bond between the
component ~urface 12 and ceramic layer 16. ~etallic
layer 14 al~o allows for a smooth transition between the
differing physical properties of the component, in this
case piston dome 10 and ceramic layer 16. More
specifically, metallic layer 14 exhibits a thermal
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expansion characteri6tic which relieves stresses that
might otherwise be created at elevated operating
temperature~.
As referenced above, metallic layer (bond
coat) 14 is preferably comprised of a MCrAlY alloy.
Such alloys have a broad composition of 17.0-23.0
percent chromium, 4.5-11.0 percent aluminum, 0.5-1.20
percent yttria, 0.0-0.20 percent iron, with M being the
balance, 6elected from the group consisting of iron,
cobalt, nickel, and mixtures thereof. Minor amounts of
other alloys such as silicon may also be present. Such
alloys are known in the prior art for use alone as a
protective coating and are described in various U.S.
patents, including U.S. Patent Nos. 3,542,530;
~,676,085; 3,754,903; 3,928,026; 4,005,989; 4,055,705;
4,339,509; 4,743,514; 4,880,614; and 4,916,022.
Still referring to Figures 1 and 2, it is
preferred that the MCrAlY layer be applied by plasma
spray deposition. However, other deposition processes
may be employed ~or producing the MCrAlY layer
~ including, for example, sputtering flame spray and
electron beam vapor deposition 60 long as a thin,
uniform thickness, hiqh integrity coating of the desired
composition results.
Ceramic layer 16 which is deposited on
metallic layer 14 is also subject to a broad composition
of yttrium partially stabilized zirconia or cerium-
yttrium partially stabilized zirconia. Applicant has
found that in the former case, it is preferred to have
a percentage of between 7.0-9.0 percent yttrium with
trace constituent6 of other elements including 0.0-1.5
per~ent S102, 0.0-0.5 percent CaO, 0.0-0.8 percent MgO,
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0.0-0.4 percent Fe203, 0.0-0.2 percent Al203, and 0.0-0.2
percent TlO2, with 2rO2 being the balance. As in the
case af the metallic layer 14, ceramic layer 16 is also
preferably deposited by plasma spray deposition.
However, other deposition processes may be employed such
as ~putterlng, flame spray and electron beam vapor
depofiition~
As referenced above, it is preferable that
metallic layer 14 have a thickness between 0.003-0.006
inches and the ceramic layer 16 have a thickness between
0.010 and 0.015 inche6 for a combined total thickne6s
between 0. 013 and 0.021 inches. It is also preferable
that ceramic layer 16 be comprised of a porous material
having between 10-15 percent volume porosity. It is
al~o preferable that particles which make-up the
metallic and ceramic layers have a spherical morphology.
Referring now to Figure 2, there is shown the
protective coating of the present invention as applied
to component surfaCe6 of applicants' Series 149 pot-type
cylinder head used ln 2-cycle compression ignitlon
internal combustion engines. In the pot-type design, a
separate cylinder head 18 is used to encase each
combustion chamber. Thus, each cylinder head 18 encases
4 exhaust valves 20.
As shown in Figure 2, the metallic and ceramic
layers, 14 and 16 are deposited only on the component
surfaces such as valve heads (combustion faces) 22, and
fire deck 24 which are exposed surface6 in the
combustion chamber. Conventional masking techniques may
be u~ed to prevent the deposition of the metallic and
cernmic coatings, 14 and 16 on non-combustion 6urfaces
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26. Surfaces 26 are recognized as contacting the engine
block and fall outside the combustion chamber.
It i6 anticipated that the thermal barrier
coating of the present invention will be applied to the
surface6 of combustion chamber components in newly
manufactured engine6. However, 6ignificant after market
work can also be performed to repair, for example,
cylinder heads and other components. Such repair work
should include the deposition of the thermal barrier
coating disclosed herein.
Referrlng now to Figure 3, there is disclosed
detailed method steps for depositing the thermal barrier
coating of the pre6ent invention on component surfaces
in compres6ion-ignition internal combustion engines. As
set forth above, it i6 recogni2ed that in the case of
certain components, such as piston domes, the component
mu6t initially be machined back to the specified coating
in order to retain the proper compression ratio. The
component surface must then be prepared by chemically
treating lt to remove dirt and oil. Prefera~ly, a
suitable vapor degreasing apparatus utilizing for
example, perchlorethylene is utilized.
Following cleaning, the component surface is
grit bla~ted in order to roughen the surface, eliminate
oxides and increase the available surface area for
deposition. The component surface 12 is grit blasted
using, for example, an aluminum oxide grit to achieve an
optimum 6urface roughness between 150-300 ~in AA.
Significantly, applicant has found that
~urface roughnesses le~s than the optimum range
re~erenced above are in~ufflclent to form a lasting
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mechanical bond with metallic layer 14 when exposed to
cyclical temperatures and compression loads such as
those exhibited by 2-cycle compression ignition internal
combustion engines. Applicant has further found that
fiurface roughne~es greater than the optimum range
cauaes ~urface component peaks to actually fold over one
another and break off thus reducing the availa~le
surface area and adhesion properties of the metallic
layer.
Still referring to Figure 3, a thin metallic
layer 14 i~ then deposlted on the roughened component
surface. As referenced above, the metallic layer i~
preferably comprised of MCrAlY material and is selected
from the group consisting of nickel base alloy
(NiCrAlY), cobalt ba5ed alloy (CoCrAlY), nickel cobalt
base alloy (NiCoCrAlY), and iron base alloy (FeCrAlY) in
accordance with the percentage weights of the preferred
embodiment referenced above. The metallic layer i5
deposited to a thickness between 0.003-0.006 inches at
an average application rate per pass less than 0.001
inches and preferably between 0.004-0.007 inches.
The metallic layer 14 is deposited directly to
the component surface 10 preferably by plasma spray
vapor deposition at a spray distance ~etween 3~ - 5
inches. In this regard, applicant has found that
distances greater than the desired range result in
unmelted or partially melted particles deposited on the
substrate. As a result, the porosity and oxide content
of the metallic layer 14 is increased and the density of
the metalllc layer 14 is decreased. As an aside, it
~hould be recognlzed that it is preferred to avoid
oxidation and to decrea~e oxide content-to obtain a
better mechanical bond between the metallic layer 14 and
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the roughened component surface 12. Thus, components
should be stored in hot, humidity-free environments
between grit blasting and the application of the
metallic bond coat 14 to avoid such oxidation.
Still referring to Figure 3, a porous ceramic
layer 16 i6 then deposited atop the metallic layer 14 to
impede the flow of heat therethrough. If applied
properly, the ceramic layer 16 will not exhibit any
deviations such as bumps or waves across the surface
contour of the component. The ceramic layer 16 will
similarly be void of spalling, cracks and blisters.
Applicants have found that chips on most ceramic coated
parts cannot extend more than 0.2~ inches away from the
edge nor be proud to the edge surface. Edge chipping is
not acceptable, however, on piston domes.
As referenced above, the ceramic layer is
preferably comprised of material having 10-15 percent
volume porosity and comprised of 7-9 percent yttrium
partially 5tabili2ed zirconia or ceria yttrium partially
~tabilized zirconia according to the compositions of the
preferred embodiments referenced above.
In the typlcal applicat~on, the ceramic layer
16 18 depoBited on the metallic l~yer 14 by the u~e of
a plasma spray gun. ~efore the respective coatings, the
ceramic and the metallic materials prefera~ly exist as
tiny spheroids. Typically, such powders are free
flowing spherical alloys, manufactured by inert gas
atomization. These particals are melted in the plasma
gun and adhere to the component surface 12 or metallic
surface 14, respectively. ~ecause the plasma spray
interacts wlth air molecules, the metallic and ceramic
co&tings 14 and 16 are porous. The degree of porosity,
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-14-
however, can be adjusted by varying the stand off torch
distance, i.e., plasma spray distance.
The ceramic layer is preferably deposited to
a thickness between 0.010-0.015 inches at an average
application rate per pass les6 than 0.001 inches and
more preferably in the range of 0.004-0.007 inches at a
spray difitance between 3~ - 5 inches. For verification
purposes, the proper thickness of both the ceramic layer
16 and the metallic layer 14 can be confirmed using a
permascope or a tinsley gauge. Similarly, compositional
requirements may be confirmed by using a 6canning
electron microscope.
In contrast to the results of varying the
spray di~tance during the deposition of the metallic
layer, applicant has found that spray distances closer
than the optimum range result in increased density and
decreased porosity which, in turn, inhibits adhesion of
the ceramic layer 16 to the metallic layer 14.
Slmilarly, the utilization of spray distances
greater than the optimum range result in increased
porosity and decreased structural integrity of the
coatlng. Under such conditions, the thermal barrier
coating has been found to fall during thermal cycling
resultlng in spallatlons.
It is recognized that the metallic and ceramic
layers may be applied by other deposition means,
including electron beam vapor deposition, sputtering,
chemical vapor deposition, powder flame spray
applicatlon and detonatlon gun application. Typical
methods of plasma-fipray coatings are more thoroughly set
forth in the publication "Plasma-Spray Coatings",
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ScIENTIFIc A~ERICAN, September 19~8, Herbert Herman, the
teachings of which are expressly incorporated herein.
While the best modes for carrying out the
invention have been described in detail, those familiar
with the art to which this invention relates will
recognize various alternative designs and embodiments
for practicing the invention as defined by the following
claims.
