Note: Descriptions are shown in the official language in which they were submitted.
-- 1 -- ' ~. ' ! i
RD-19.431
~ INFORCED MICROL~U~INATED
koET~L-ML~TRIX-CO ~ OSITE STR~CT~
CROSS-REFERENCE TO RELATED APPLICATION
The present invention is closely related to
application Serial No. (Attorney docket RD- ), filed
, the text of which is incorporated herein by
reference.
BAC~GROUND OF THE INVENTION
The present invention relates generally to
microlaminated metal-matrix-composite structures formed from
deposits of a first metal either with a second metal, or with
a ceramic material, in structures which have a generally
laminated configuration. More specifically, it relates to
laminar structures which are formed with metal matrices and
with reinforcing members extending between the layers of the
microlaminar struc~ure and to the methods of forming such
structures.
The formation of generally laminar structures of
two different materials has been described in the art. One
such prior art publication is entitled "Production of
Composite Structures By Low Pressure Plasma Deposition".
This article was published in Ceramic Engineering and Science
Proceedings, Vol. 6, No. 7-8 (July/August 1985). This
article describes structures which are similar to but not the
same as the structures which are taught and claimed in the
subject application. The prior art structures are formed by
plasma deposition. For example, in Figures 7 and 8 of the
article, structures are shown which have a generally laminar
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f~ ` .7 ;J I J
Rp-19~431
configuration. In the structure of Figure 7, a superalloy is
formed into a first set of laminae and chromium carbides,
Cr3C2, forms the second or other set of laminae of the
structure. In the structure of Figure 8, the laminar
configuration of the alternating layers of superalloy and
aluminum oxide are displayed.
Five other papers dealing with plasma sprayed
coatings are as follows:
(1) R.~. Bunshah, C.V. Deshpandey, and B.P. O'Brien,
"Microlaminate Composites - An Alte~native Approach to
~hermal Barrier Coatings", Paper presented at the Thermal
Barrier Coatings Conference, NASA-Lewis, Cleveland, OH (May
1985).
(2) J.R. Rairden and D.M. Gray, "Study of Coordinated
Two-Gun RSPD (Rapid Solidification Plasma Deposition)
Processing to Achieve Size and Shape Control", GE Report No.
88~RD147 (June 1988) Class 1.
(3) J.R. Rairden and D.M. Gray, "The Deposition of
Turbine Blade Coat ~ngs Using Low-Pressure, Multigun Plasma
Spray Processing~, published in the Trans. of the First
International Conference on Plasma Surface Engineering, held
at Garmisch-Partenkirchen, F~G (September 19 23, 1988).
(4) P.A. Siemers and W.B. Hillig, "Thermal-Barrier-
Coated Turbine Blade Study", Report No. NASA CR-165351, SRD-
25 81-083 (August 1981).
(5) G.P. Liang and J.W. Fairbanks, "Heat Transfer
Investigation of Laminated Turbine Airfoils", Transactions of
Gas Turbine Heat Transfer Symposium, pages 21-29, Winter
Meeting of ASME, San Francisco (1978).
One of the problems which has been encountered in
the formation and in the use of structures as disclosed in
these articles is that they can lose some of their beneficial
properties when they are subjected to extensive thermal
cycling. By thermal cycling is meant that the structure is
: '
. . . . ~ ~ ~ r.;
RD-19,431
heated as, for example, to a service temperature of over
1000C and then cooled to room temperature or even lower
temperatures and then again heated and cooled, and etc. This
thermal cycling has been recognized as a source of crack
propagation in structures such as those described in the
referenced article. Thus, where a relatively small crack
develops in one of the ceramic lamina of a structure, the
thermal cycling of the structure tends to cause propagation
of the crack because of the stress induced due to the
relatively large mismatch of the thermal coefficient of
expansion of the metal member of the composite relative to
the ceramic layers of the composite. The effect of
propagation of a crack or cracks preferentially through one
layer or laminar of the composite structure is to effectively
cause a delamination of the structure. The impetus of
driving force for such delamination is, as noted above, an
extension of a crack formed, for example, in a ceramic layer
of the composite through that layer and, accordingly,
weakening and destroying the otherwise strong bond which may
~0 exist between the several laminae of the structure.
BRIEF STATEMENT OF THE INVENTION
It is, accordingly, one object of the present
invention to provide microlaminated structures which minimize
or eliminate the tendency of the structures to delaminate.
Another object is to provide microlaminated
structures which display an ability to retain their laminar
form.
Another object is to provide a microlaminated
structure having a high strength to weight ratio.
Another object is to provide a microlaminated
structure having low density and high elastic modulus.
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RD-19,431
Another object is to provide a microlaminated
structure havin~ controlled thermal expansion.
Another object is to provide a microlaminated
structure having a controlled thermal conduction.
Another object is to provide a microlaminated
structure having a controlled electrical conduction.
Another object is to provide a microlaminated
structure which retains its laminar form while undergoing
stress due to long-term ~hermal cycling or any other stress-
inducing force.
Another object is to provide a method of limiting
the growth of cracks in the microlaminae of composite laminar
structures.
Other objects will be in part apparent and in part
pointed out in the description which follows.
In one of its broader aspects, objects of the
present invention can be achieved by providing a first plasma
gun adapted to plasma spray deposit a first material, and by
providing a second plasma gun adapted to plasma spray deposit
a second material. These two independent guns are aimed at a
common zone of a receiving surface and plasma spray deposit
is formed in the ~one by the simultaneous combined spray
deposit from both guns. It is found that the structure which
is formed has a swirl configuration so that strands of
reinforcement form extending between the laminae of the
deposited structure and the resulting structure is capable of
resisting delamination due to thermal cycling or other
reasons. The swirl configuration of the structure is formed
because the two distinct ingredients from the two separate
guns are microlaminated or intermi~ed and finely
interdisbursed as they are deposited so that they form a
microlaminated structure.
By microlaminated and/or intermixed and/or a
similar term as used herein is meant that the metal forms, in
-- 5 --
~ Rn-14.43
J ~ .
essence, the continuous phase because the swirl formation of
the deposited metal intermixes with ceramic to a degree which
makes the metal dominate in the properties of the composite.
While the low pressure plasma spray process was
used to form all of the materials described herein below, it
would also be possible to use conventional atmospheric
pressure processing to form the microlaminated structures
described.
BRIEF DESCRIPTION OF THE DRA~INGS
The description which follows will be understood
with greater clarity if reference is made to the accompanying
drawings in which:
F~GUR~ 1 is a schematic illustration of the arrangement
of two plasma spray guns relative to a substrate on which a
combined plasma spray deposit is being formed;
FIGURE 2 is a side elevation (A) and end elevation (B)
of a coupon on which plasma spray deposits were made;
FIGURES 3-5 are examples of the metallographic
characteristics of a microlaminated structure, in this case,
of NiCrAlY/Al2O3; and
FIG~RE 6 is a graph in which percent expansion is
plotted against temperature for a set of materials.
DETAILED DESCRIPTION OF THE INVENTION
One of the findings which is most significant in
developing the structurally sound coatings is the finding
that the simultaneous use of two different plasma spray guns
having distinct ingredients in the separate guns results in
the formation of a deposited layer having a distinctive
structure. The distinctive structure is distinctive on both
the macro and on the micro scale. In particular, the
~ RD-19.431
structure has a swirl-like intermixing of the different
elements from the two guns so that there are essentially no
continuous laminae present in the formed structure and there
is, accordingly, no tendency for delamination to occur. This
swirl-like structure is apparent on both a macro and micro
scale. That is, the swirl-like structure can be seen with
the unaided eye and can also be seen under magnification.
There are a number of parameters which are
important in achieving the swirl-like intermixed and
interlocked structure of a deposit made up of the two
separate ingredients delivered to the surface from the
separate guns.
A first parameter is the aim-point of the two guns.
Generally, it is desirable to have the aim-points of the guns
coincide so that a deposit is being applied to the same area
of the receiving surface from each gun. The aim-point may be
determined, for example, by projecting an imaginary line
through the nozzle of a gun and determining where the line
will intercept the receiving surface at which the gun is
aimed. An aim point can also be determined experimentally by
observing where the center is located in a deposit from a
stationary gun. It has been demonstrated that where the two
aim points for the two guns coincide, the spray deposit which
is delivered has a swirl-like configuration over the entire
extent of the area where deposit is being made from each gun.
Another parameter is the angle of separation of the
imaginary aimlines extending from the guns. This angle of
separation is determined, in part, by the geometry of the
guns themselves. For example, the EPI guns ~Electro Plasma,
Inc., Irvine, CA) are physically larger than guns
manufactured by Metco (Perkin Elmer Metco, Westbury, NY) so
that the minimum angle of separation will be greater for a
setup employing the EPI guns than for one employing the Metco
guns. In general, we have found that it is desirable to use
R~i - 19, 9 31
a minimum angle of separation so that the deposit angle from
each gun is as near to perpendicular to the receiving surface
as is physically possible for the guns employed. The use of
the 90 deposition angle, that is where the imaginary aim
line is approximately perpendicular to the receiving surface,
results in the deposit of the most dense layers of deposited
material.
My experience has shown that the deposition angle,
that is the angle formed by the imaginary aimline and the
surface to which the deposit is to be made, must be at least
70 to achieve a high density deposit.
At deposition angles of less than 70 the deposit
becomes increasingly porous as the deposition angle is
reduced. Swirl-like structure is found in such less dense
deposits however. Where a controlled porosity is preferred,
a deposition angle of less than 70 can be employed. Some
experimentation to determine the degree of porosity ~hich is
developed relative to the deposition angle may be employed to
ensure that a desired porosity of a deposited layer is
achieved. The use of porous thermal barrier coatings is
feasible and the subject invention is particularly useful in
improving the internal structure of the thermal barrier
coatings so that laminar structures are avoided and
interlocked swirly-types of structures are formed. The use
of lower deposition angles ls deemed to have an influence on
the bonding of a coating to a substrate surface and the
formation of the more porous coatings may limit the bonding
of coatings on a receiving substrate.
Another parameter in the formation of the layers of
this invention is the distance from the gun to the substrate.
Generally, this distance ranges from about 8 to about 18
inches in low pressure plasma deposition and about 3 to 6
inches in atmospheric pressure plasma deposition. The
distance is selected based upon spray pattern size desired.
~ ,) ,'`J RD-19 431
Larger spray patterns are developed when the guns are held at
a greater distance from the receiving surface. Another
factor concerned with the dis~ance is the heating of the
substrate. Some heating is required to obtain a good bonding
of the coating to the substrate and the shorter the distance
of the gun to the substrate the greater the degree of heating
of the substrate surface. This factor is one which can be
determined with comparative ease by a few scoping tests to
balance the requirements of a particular coating substrate
combination. The factors involved are those indicated above,
namely the degree of heating of the substrate where shorter
distance increases the degree of heating, and the desired
size of spray pattern on the receiving surface where greater
distance increases the size of the spray pattern. Preheating
a substrate, that is, before spray deposit starts, can be
done very effectively with the plasma of a plasma gun.
The suppliers of guns which have been used
successfully in the practice of the present in~ention are:
Electro Plasma Inc., 16842 Milliken Avenue, Irvine, CA
92714;
Perkin Elmer Metco, 1101 Prospect Avenue, Westbury,
L.I., ~JY 11590; and
Plasma-Technik, AG, Rigackerstrasse 21, 5610-Wohlen,
Switzerland.
A further parameter involved in the practice of the
invention is the size of the powder particles which are
employed in forming the deposited layer. The particle sizes
are selected based upon the melting characteristics of a
material in the plasma. As an illustration, for metals such
as nickel-based alloys, deposited at low pressure, a powder
size of about 400 mesh or about 37 ~m with an average size of
about 20 ~m has been found satisfactory. For lower melting
point metals such as copper, a larger particle size such as a
270 mesh or about a 53 ~m size can be used successfully.
_ 9 _
~ ; R~-19.431
Conversely, for refractory metals and ceramics, a powder size
of 10-20 ~m is required in order to obtain a satisfactory
melting of the particles and in order to form the swirly-type
structure in the layer.
The primary criteria for the selection of a powder
size is that the powder must be of a size so that it will
melt when passing through the plasma and that it can be fed
to the plasma gun using available powder feeders. In this
regard, essentially any material that can be melted without
decomposition can be plasma spray deposited.
An additional parameter concerned with the practice
of the present method is the powder feed to and through the
plasma gun. Powder feed mechanisms are commercially
available and are suitable for use in connection with the
present invention. Powder feed rates can be as high as 50
pounds per hour for a nickel-based alloy, for example. In
general, feed rates of a few pounds per hour to as high as 20
pounds per hour are generally employed in the practice of the
present inven ion.
Also, by using two guns as described here, graded
composition coatings can be formed to tailor the properties
of the coatings for particular applications. For instance,
to minimize stress at a coating/substrate interface, the
coating composition may be varied from high metal content at
a metal substrate to high ceramic content at the outer
surface; This can be done simply by varying the rates of
powder feed to each gun during the deposition.
The carrier gas employed in connection with the
invention has generally been argon. Flow rates used depend
upon the particle size and density of the powder being fed
and the velocity required for injection of the particles into
the gun. Generally, the processing conditions recommended by
the gun manufacturer are used. The flow rates of 10-40
standard cubic feet per hour would be typical in practicing
-- 10 --
~ r'' '~ R~-l4.431
the present invention. The plasma gas employed in the
operation of the plasma gun is typically a mixture of argon
and helium or argon and hydrogen. Gas flow and gas
composition for any particular powder are selected to achieve
a desirable particle heating capability. Here it is
conventional to do some scoping tests in order to provide the
proper balance of parameters.
The method of practice of the invention and the
combination of parameters found suitable are described
illustratively in the following examples:
In this example, thermal barrier coatir,gs were
deposited using two plasma spray guns mounted in a water-
cooled low pressure chamber having dimensions of l.44 metersin diameter and l.37 meters in length for preparing plasma
spray deposits. The guns were held stationary in positions
having a common aim point and the receiving substrate was
moved to produce the desired intermixed deposit on the chosen
surface of the substrate. The guns were 80-kW EPI guns,
Model 03CA. The guns were mounted on brackets that permitted
the positioning of the guns at different angles with respect
to a receiving substrate. The guns could be positioned as
close as 9 centimeters apart. The guns could be angled over
a wide range of angles so that the gun-aim-points were at the
same area of the substrate and the spray patterns of the two
separate guns overlapped in the manner schematically
illustrated in Figure l.
The guns were positioned about 43.2 centimeters
from the substrates on which the deposit was to be formed.
The powders employed in this study were as follows:
(1) Amdry 962, Ni-22Cr-lOAl-l.OY, obtained from Alloy
Metals, Inc.
~ RD-19 43
(2) Amdry 995 powder having a composition of Co-32Ni-
2lcr-8Al-o.sy~ also obtained from Alloy Metals, Inc.
(3) 105 SFP aluminum oxide powder obtained from Perkin-
Elmer-Metco Corporation.
(4) ZrO2-8 wt% Y203 (-44~m + lO~m) obtained from Corning
Glass Works.
The deposition conditions are given in Table I.
TABL~ I
1~
Plasma Deposition Conditions
80-kW Guns
Anode 03-CA-110
Primary gas 122 l/min Ar
Secondary gas 32 l/min He
Powder feed gas 5.6 l/min Ar
Power 1700 A, 44V
System pressure 60 mm Hg
In this example, one gun was used to spray metal
powder and the other gun was used to spray ceramic powder.
Two metal powders, NiCrAlY (Amdry 962) and
CoNiCrAlY (Amdry 995) were sprayed in separate runs by the
first gun. Two ceramics, Al2O3 (Metco 105SPF) and Zro2y2o3t
were sprayed by the other gun.
Four runs were made as follows:
TABLR II
First Gun ~ssnn~_~n
1 NiCrAlY A12O3
35 2 CoNiCrAlY Al23
3 NiCrAlY ZrO2 Y2O3
9 CoNiCrAlY ZrO2 Y2O3
- 12
Rn-l9~4
As a measure of preparation for forming the plasma
spray deposits, the substrates were first heated in the
plasma flame to about 900C and the substrate surface was
reverse transferred arc cleaned prior to commencing the
coating deposition.
A number of substrates were employed to receive the
deposits which were then subjected to thermocycling tests to
test for delamination. These substrates were cast René ~0
coupons having configurations as illustrated in Figure 2.
These coupons were about lt2 inch in width, 1/4 inch in
thickness, and about 1-3/4 inch in length. The coupons were
supported from a holding rod extending from one end and
welded thereto by Inconel 82 weld filler. A thermocouple
hole was drilled in the end of the coupon opposite that from
which the holding rod extended.
Cyclic oxidation tests were performed by exposing
coupons alternatively in a static furnace at 1150C for S0
minutes and in room air for 10 minutes. Weight c~ange
measurements were recorded during the 10-minute room air
period of the oxidation cycle. Metallographic examinations
were made by cutting transverse slices off the coupons.
From these tests, it was concluded that the Al2O3
is preferred to the ZrO2-Y2O3 as an oxide for incorporation in
the MCrAlY metals, where M is Ni, Co, or some combination of
Ni and Co. The composites containing the Al2O3 ceramic had
superior strength and durability.
This example also demonstrated an important aspect
of the subject method. That aspect is the ability to tailor
the composite structures which are formed. By tailoring is
meant that the ingredients themselves as well as the delivery
of the molten oxide and molten metal to the receiving surface
can be controlled and varied to impart to the formed deposit
a desired set of properties within a broad envelope of
- 13 -
, ~. . , ,:
R~-19.43
properties attainable with the combination of ingredients
used.
In the above example, the coatings were prepared as
thermal barrier coatings. The coatings containing the
S zirconia were found to have lower durability and were also
found to be subject to greater oxidation than the coatings
containing the aluminum oxide.
Thermal conductivity tests showed that the
NiCrAlY/alumina composite has about 40% of the thermal
conductivity of NiCrAlY.
EXAMPLE 2: High Strength, Low Density, Free-Standing
Microlaminated Composites of Xené 80/Al203
The procedures and apparatus of the above example
were again used to form microlaminated composites.
In this case, an investigation was conducted of
formation of microlaminated composites of René 80 with
aluminum oxide to evaluate the potential of use of such
material where high strength to weight ratio properties and
high modulus properties are needed. Two specimen types of
the microlaminated René 80/A1203 composites were made:
(1) Two deposits about 1.5 millimeters thick by 10
centimeters long by 3.8 centimeters in diameter on steel tube
mandrels were formed. The René 80/A1203 volume ratios of the
25 tubes extended from 80-20 to 20-80. Five tube specimens
having different ratios as follows were prepared: 80:20;
65:35; 50:50; 35:65; and 20:80. A gun separation angle
corresponding to the angle theta of Figure 1 OI 45 was used
to form tubes of each composition.
(2) A second set of tubes having René 80/Al~03 volume
ratios were prepared having a gun angle of 10. These tubes
had metal to oxide ratios of 65:35; 50:50; and 35:65. The
second set of tubes was prepared to study the effect of the
gun angle parameter on the microstructure of the tubular
~ RD-lqr43
deposits formed. In general as noted above, such tubular
structures are formed by maintaining the plasma guns
stationary and moving the tubular substrate both by rotation
and by axial motion.
From the tube deposit tests made employing the René
80 and aluminum oxide, it was determined that at volume
ratios of less than 50 to 50, the structural integrity of the
deposit is poor. I found that the deposits with metal oxide
volume ratios of 35 to 65 and 20 to 80 tended to break apart
and this evidence of breakage was found even before the
removal of the mandrel. The micrographs of Figures 3, 4, and
5 illustrate the three different ratios employed in forming
the structures. Figure 3 is a micrograph at 400
magnification of the structure formed from 65 volume % Al2O3
15 and 35 volume % R-80. The structure of Figure 4 is formed
from a composition of 50 volume % of Al2O3 and 50 volume
percent R-80. The structure of Figure 5 is formed from a
composition having 35 volume % Al2O3 and 65 volume percent
René 80.
The René 80 powder employed in these experiments
was a 400 mesh powder having an approximate average particle
size of about 20 microns. The alloy René 80 is a
commercially available alloy which has a composition by
weight of 9.5 % cobalt, 14.0 % chromium, 3.0 % aluminum, 5.0
25 % titanium, 4.0 % molybdenum, 4.0 % tungsten, 0.03 weight %
zirconium, 0.015 % boron, and 0.17 % carbon, the balance of
the alloy being nickel. The powder was obtained from Alloy
Metals, Inc.
The aluminum oxide was 105 SPF aluminum oxide which
was obtained from Perkin Elmer Metco Corporation.
The microstructures of the two deposits as
illustrated in Figures 3, 4, and 5 demonstrate that the
microstructure form is basically the swirly configuration
which I have associated with the improvement in properties
f` ~ Rr)- 1 9 . 4 31
which are found. Further, it is evident that from these
microstructures that even though the phase distribution is
not uniform, there is a fine interdispersion of the two
phases. This is what gives the structure the benefit of the
microlaminated construction which is responsible for the
improved properties.
No gross microstructural differences were noted as
a function of the angle between the guns. However, the
properties data summarized in Table III do indicate that the
guns' angle may be significant. Table III presents a summary
of the experimental procedures employed in the study and
experimental results which were found.
/
1 6
RD-l 9, ~31
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~ RD-19.431
The compositions of the deposits ~ormed using an
angle between the guns of 10 as determined by image analysis
data tend to be closer to the compositions aimed for based on
powder feed rate. In all of these deposits, except for the
50:50 deposit of René 80/Al203 using the 10 gun angle, the
René 80 content was below the aimed composition. An angle
between guns of 10 was used for the remainder of the test
samples. Some additional information can be noted from the
data presented in Table II. As noted in the Table, there was
heat treatment applied to the deposits. The data in the
Table indicates that there was little effect of heat
treatment on the density of the deposits measured. However,
the elastic modulus values and the 3 point bend strengths did
increase as a result of the heat treatmen~ applied as listed
in the Table.
Secondly, from the data listed in Table III, it can
be observed that the expansion coefficients decrease and the
electrical resi~stivities increase with increasing Al2O3
content. These data are consistent with the rule of mixtures
consideration.
Plate deposits having a thickness of about 2.5
millimeters were formed on copper plate mandrels having
dimensions of 15.2 x 15.2 centimeters. These deposits were
also formed by holding the guns stationary and moving the
plate substrate to receive the deposit. The plates were
moved in both an x and y direction to expose the entire
surface of the plate mandrel to the coincident plasma sprays.
In making these deposits, the angle between the guns was 10.
The René 80/Al203 volume ratios employed in making the
microlaminated deposits on the plate mandrels were 80:20;
75:25; 65:35; and 50:50.
The data obtained from the preparation and testing
of the plate deposits described and discussed above are set
forth in Table IV immediately below:
- 18 -
: ~ ~ .Rn-19r43
TABLE IV
Tensile Test Properties of Microlaminated René 80/Al203 Plates
Specimens heat treated 2 hr., 1250C, Ar except as noted
Aim v/o Composition Test Temp. 0.2% YS UTS
René 80 Al23 (C~ (ksi) (ksi) R/A
RT llQ.7 0
560 107.5 0
710 113.4 0
860 88.1 88.4 Small
1010 35.5 36.3 Small
RT 118.8 Small
560 98.1 0
710 111.3 111.3 Small
860 82.9 82.9 0
1010 36.0 36.1 Small
RT 102.8 0
560 80.9 0
710 91.3 91.3 Small
860 77.6 77.6 Small
1010 39.2 39.4 Small
65* 35 RT 127.8 Small
560 115.5 0
710 113.9 116.7 Small
860 88.0 88.9 Small
1010 34.9 36.0 Small
RT 71.5 0
560 66.0 0
710 No data
860 64.8 64.8Small
1010 36.7 0
100** RT 140 195 17.0
710 110 165 22.0
1010 30 40 10.0
* - Specimens not heat treated
*~ - Representative data from previous studies
- 19
1" ' ' ,. - 'i,, RD-19.431
As is evident from the data included in the Table,
the volume % ratios sought in preparing compositions were 80-
20; 75-25; 65-35; 65-35 which specimen was not heat treated;
and 50-50. Data from a representative previous study is also
included where René 80 would be 100%. The ratios listed in
the Table were deposited using powder feed volume ratios as
set forth. Sheet tensile specimens were cut from the plates.
The results of the tests from room temperature to 1010C are
summarized in Table IV. These data can be compared with
representative tensile data for rapidly solidified plasma
deposited René 80 as set forth next to the 100% René 80 data.
There is a large decrease in axial tensile strength and
ductility at lower temperatures for the microlaminated
composites as compared to a rapidly solidified plasma
deposited René 80 sample. The trend is for tensile strength
to decrease with increasing A12O3 content. It should be noted
that the 3 point bend strength values for the René 80 Al2O3
microlaminated specimens of Table III are significantly
higher than the axial values. In addition, the axial tensile
strengths of the microlaminated composites are almost equal
to the rapidly solidified plasma deposited René 80 at 1010C.
The data suggests that there may be an advantage to the use
of the microlaminated composite because of lower density and
higher elastic modulus for those applications in which the
low ductility can be tolerated.
From the foregoing, it is evident that a unique
material may be tailored pursuant to the present invention to
have high strength a~ low density, and accordingly to have a
high strength to weight ratio. Also, it is evident that the
density of the material can be tailored to a desired value by
changing the properties of the ing edients used.
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~ R~-19 431
EX~æLE 3: Free-standing Microlaminated Composites of
Invar:/A1~03
It became clear from the above examples that a wide
variety of custom properties could be incorporated in various
structures prepared pursuant to the present invention.
As a further illustration of this capability, a
free standing material suitable for packaging for
microelectronics was prepared. This material was to have a
very low thermal coefficient of expansion and very low
density. Invar metal was selected because it has a low
coefficient of expansion. However, it is a weak metal and
has a low modulus. It was sought to increase its strength
and its modulus and to decrease its coefficient to expansion.
lS The apparatus and methods of the previous examples were again
employed. Using these methods and apparatus, the properties
of microlaminated composites of Invar/A1203were investigated
to determine if the low coefficient of expansion properties
could be retained in a lower density, higher elastic modulus
and higher strength material. Plates of the microlaminated
Invar/A1203composite were deposited using the following
powder feed ratios by volume: 63:35; 50:50; and 35:65.
The properties of these materials were measured as
described above and these properties are summarized in Table
V which is set forth immediately below.
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.i RD- l 9, 4 31
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- 22 -
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; i R~-19,4
The microlaminated sample of 35 Invar/65 Al2O3
formed on the plate was found to be extremely brittle and so
brittle, in factr that i~ could not be machined into a
mechanical test specimen. From the Table V, it can be seen
that the Invar content of these microlaminated plates was
lower than the target content and, accordingly, was lower
than expected based on the powder feed rate for all the
specimens. This lower figure for the metal component of the
composite is similar to the data already discussed for the
microlaminated composition containing René 80 and Al2O3.
However, this lower value can be overcome by adjusting the
respective feed rates to feed a higher level of metal to
bring the density and other properties to a desired level
within the range of densities available and consistent with
achieving a desired overall set of properties.
The elastic modulus properties of the
microlaminated Invar/Al2O3 specimens are about 50% higher than
the elastic modulus of Invar and the electrical resistivity
of the microlaminated samples was observed to increase with
increasing Al2O3 content.
A minimum in expansion coefficient at a volume
ratio of about 40% Invar/60% Al2O3 was indicated. The data
obtained indicate that the microlaminated Invar/A12O3
25 compositions can be identified with a thermal expansion ;-
coefficient approximating that of Invar.
From the data obtained from this evaluation of the
microlaminated Invar/Al2O3 compositions, it appears highly
probable that material can be developed from these
ingredients which display low density, low thermal expansion,
high elastic modulus, and reasonable strength properties as
compared to Invar per se.
- 23 -
RD-19.43L
EXA~ 4: Free-standing Microlaminated Composites of
- Copper and A1203
The properties of microlaminated copper/aluminum
oxide deposits were explored for potential application and
power hybrid microelectronics. A series of microlaminated
samples of copper and aluminum oxide were formed on plates as
described above in Example 3. The deposits on the plates
were formed using feeder/rate volume % ratios of 65:35;
50:50; and 35:65. The properties of these materials are
summarized in Table VI.
-
'',., ~ ` ~
.,''',` l
`- ~` " ' l
~ !
., .
-- 2~1 --
, ~, ,,~,,
N 4 ~1 0 ~; ~o
Y Y ~ o~
A = , . ~ ~ _ ~ _
Eo ~"A ~
~ !" ~ 1~ ~ 8 g ~
~ - R~-l9~a3l
,~. .., , . ~, -
For these plates, the image analysis data appear to be
misleading. Based on the measured density values, the copper
content of the 65 volume % copper, 35 volume % aluminum
oxide, and of the 50 volume % copper and 50 volume % Al2O3
plates are higher than the aimed compositions.
It can be noted from the data included in Table VI
that the electrical resistivity values increase and the
thermal expansion coefficient values decrease systematically
with increasing Al2O3 content. The elastic modulus values
reflect the Al2O3 content in the microlaminated composites.
From the foregoing, it is evident that metal matrix
composite structures can be formed by low pressure plasma
deposition using the coordinated two-gun process of the
subject invention.
By microlaminated and~or intermixed and/or terms of
similar import as used herein it meant that the metal forms,
in essence, the continuous phase because the swirl formation
of the deposited metal intermixes with ceramic to a degree
which makes the metal dominate in the properties of the
composite.
These deposits can be used as coatings or as free
standing bodies. The structures can be employed in a number
of specific applications. For example, they can be employed
in oxidation and hot corroslon resistant materials. Further,
they can be employed as thermal barriers or insulating
barrier materials. Further, the structures can be employed
as structural materials per se.
The metal matrix composites employing the swirl-
type microstructure of the present invention are a class ofadvanced materials that hold promise for meeting a wide
variety of industrial requirements. A number of potential
property advantages of such structures make them particularly
useful in such applications. Among these advan~ages are the
- 26 -
, ~ ,.
~ RD-19.43
high strength to weight ratio; low density; high elastic
modulus; controlled thermal expansion; and controlled thermal
and electrical conduction. An important aspect of the
invention is that materials can be tailored to have a desired
S combination of these advantageous properties.
One of the processing techniques which is
particularly suitable for the formation of structures as
provided pursuant to the present invention is the low
pressure plasma deposition techniques such as are taught in
the patent 4,603,568. The text of the patent is incorporated
herein by reference.
A distinction from the 4,603,568 teaching as
carried out in the present invention is that the metal
sprayed from one gun is combined instantaneously with the
ceramic sprayed from the other gun in a low pressure plasma
deposition chamber where both guns are aimed simultaneously
at the same deposit zone of a receiving surface. ~hat was
achieved by the examples recited above wa~ a simultaneous
bombardment of the substrate ~ith splatters of both materials
so that the two phases were interminqled and combined into a
fine swirly anisotropic distribution.
The microstructure formed was deemed to have
durability because of the effect of minimizing the tendency
to form extensive continuous layers of ceramic. Such
continuous layers of ceramic are subject to forming planes of
weakness particularly during thermal cycling. The work
per~ormed, as represented by Examples referred to above,
demonstrated the potential of forming free standing
composites and coating composites using the coordinated two
gun low pressure plasma deposition processing. It was thus
demonstrated that a fine interdispersion of the two material
phases could be achieved and that these phases are present in
a swirly intermingled microstructure. The property data
obtained indicate the potential of this system for tailoring
RD-l 9. a31
composite materials using the rapid solidification plasma
deposition simultaneous processing of metal and ceramic
materials to meet a variety of application requirements. In
this regard, it has been demonstrated that density values can
be lowered by combining ceramic with metal. Further, elas~ic
modulus values of the composite can be increased by altering
proportions of the deposited materials, and particularly by
increasing the ceramic component of the composite. The
overall thermal expansion coefficients of the deposit can be
decreased by employing the combination of metal and ceramic
materials. The control of coefficient is illustrated in the
graph of Figure 6. Thermal conductivity values can be
increased or decreased by judicious choice of material
components for a composite system.
The use of the system makes a number of processing
advantages available and these include the use of the optimal
spray parameters for each of the materials. In other words,
the optimal spray parameters for the metal are going to be
different from the optimal spray parameters for the ceramic.
However, since the two guns are employed simultaneously but
independently, the operating parameters of the guns can be
adjusted to the best parameters for the material processed
through that gun.
It will be understood that the invention is not
limited to the employment of only two guns but that more than
two guns can be employed to achieve dissimilar surprisingly
advantageous structures through the development of the swirly
intermixed microstructure.
Another advantage of the simultaneous two-gun
processing is that the deposition angles of each material can
be varied to maximize the degree to which the microstructure
is intermixed and swirly and hence improved in durability.
- This is another favorable property of the deposit.
- 28
RD-14,431
A further advantage is that separate powder feeders
can be used for each material to eliminate potential problem
of separation due to density differences during processing
when a physical mixture of two materials is used.
