GB2239462A

GB2239462A - Microlaminated structure formed using two plasma guns

Info

Publication number: GB2239462A
Application number: GB9027564A
Authority: GB
Inventors: Iii John Ruel Rairden
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1989-12-26
Filing date: 1990-12-19
Publication date: 1991-07-03
Also published as: CA2025302A1; IT9022467A0; IT9022467A1; FR2656335A1; IT1243498B; DE4040893A1; GB9027564D0; JPH04116149A

Abstract

Two separate plasma spray guns as shown in Fig 1 are employed simultaneously to spray a first metal from the first gun and to spray a second metal or a ceramic material from the second gun. The guns have a common aim point and the deposit formed has a swirl-like intermixed and interlocked structure or microlaminated structure. In this microlaminated structure interlayer reinforcing strands extend from one splat to another of said structure. <IMAGE>

Description

4 1 :;;:> -;_> 3 G, -S> MICROLAMINATED STRUCTURE The present invention

relates to microlaminated structures and to methods of forming such structures. Illustrative embodiments of the invention relate 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, to laminar structures which are formed with metal matrices and with reinforcing members extending between the layers of the microlaminar structure and to 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 Proceedincla, 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

RD-1 9, 4 31 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.F. Bunshah, C.V. Deshpandey, and B.P. 01Brien, I'Microlaminate Composites - An Alternative Approach to Thermal 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. 8SCRD147 (June 1988) Class 1.

(3) J.R. Rairden and D.M. Gray, "The Deposition of Turbine Blade Coatings Using Low-Pressure, Multigun Plasma Spray Processing", published in the Trans. of the First International Conference on Plasma Surface Engineering, held at Garmisch-Partenkirchen, FRG (September 19-23, 1988).

(4) P.A. Siemers and W.B. Hillig, "Thermal-Baz-rlex- Coated Turbine Blade Study", Report No. NASA CR-165351, SRD 81-083 (August 1981).

(5) G.P. Liang and J.W. Fairbanks, 'Weat Transfer investigation of Laminated Turbine AIrfolls% 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 1 1 RD-1 9. 4 31 heated as, for example, to a service temperature of over 10000C 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 aiticle. Thus, where a relatively---pmall 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 exist between the several laminae of the structure.

Illustrative embodiments of the invention seek to provide:- microlaminated structures which minimize or eliminate the tendency of the structures to delaminate; microlaminated structures which display an ability to retain their laminar form; a microlaminated structure having a high strength to weight ratio; a microlaminated structure having low density and high elastic modulus; RQ19,411 a microlaminated structure having controlled thermal expansion; a microlaminated structure having a controlled thermal-conduction; a microlaminated structure having a controlled electrical conduction; a microlaminated structure which retains its laminar form while undergoing stress due to long-term thermal cycling or any other stress-inducing force; and/or a method of limiting the growth of cracks in the microlaminae of composite laminar structures.

According-to an illustrative method of the present invention ther e is Drovided a first clasma gun adapted to plasma spray deposit a first material, and 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 zone 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 co'nfiguration of the structure is formed because the two distinct ingredients- from the two separate guns are microlaminated or intermixed and finely interdisbursed as they are deposited so that they form a microlaminated structure.

By microlaminated andlor intermixed and/or a similar term as used herein is meant that the metal forms, in Rr)-1 9. 4 31 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.

For a better understanding fo the present invention, reference will now be made by way of example to the accompanying drawings in which..

FIGURE 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 NiCrAWA1203; and FIGURE 6 is a graph in which percent expansion is plotted against temperature for a set of materials.

One of the findings which is most significant in developing the structurally sound coatings i--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 k 1 RD-1 9. 4 31 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 k RD-19. 431 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.

Experiments have 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 700 can be employed. Some experimentation to determine the degree of porosity which 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 present structure 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 is 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 form-ation of the layers of 3.0 the_present structure 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.

k 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 distance 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 invention are:

Electro Plasma Inc., 16842 Milliken Avenue, Irvine, CA 92714; Perkin Elmer Metco, 1101 Prospect Avenue, Westbury, L.l., NY 11590; and Plasma-Technik, AG, Rigackerstrasse 21, 5610-Wohlen, Switzerland.

A further parameter involved 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--8lloys, deposited at low pressure, a powder size of about 400 mesh or about 37 gm with an average size of about 20 gm has been found satisfactory. For- lower melting point metals such as copper, a larger particle size such as a 270 mesh 6r about a 53 gm size can be used successfully.

1 1 k RD-1 9. 4 _1 Conversely, for refractory metals and ceramics, a powder size of 10-20 gm 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 invention.

Alsof 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 1 Rr)-1 9. 4 31 the present 'invention. The plasma gas employed in the operation of the plasma gun is typically a mixturi 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.

Methods of practice of the invention and the combination of parameters found suitable are described illustratively in the following examples:

EXAMPLE 1

In this example, thermal barrier coatings were deposited using two plasma spray guns mounted in a water- cooled low pressure chamber having dimensions of 1.44 meters in diameter and 1.37 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 1.

The guns were positioned about 43.2 centimeters 30- from the substrates on which-the deposit was to be formed.

The powders employed in this study were as follows: (1) Amdry 962, Ni22Cr-10A1-1.0Y, obtained from Alloy Metals, Inc.

1 f - 1 1 - RD-19, 431 (2) Amdry 995 powder having a composition of Co-32Ni 21Cr-SA1-0.5Y, also obtained from Alloy Metals, Inc.

(3) 105 SFP aluminum oxide powder obtained from Perkin Elmer-Metco Corporation.

(4) Zr02.8 wt% Y203 (-44pn + 1Ogm) obtained from Corning Glass Works.

The deposition conditions are given in Table I.

TABLE I

Plasma Deposition Conditions 80-kW Guns Anode 03-CA-110 Primary gas 122 1/min Ar Secondary gas 32 1/min He Powder feed gas 5.6 1/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, A1203 (Metco 105SPF) and Zr02Y203, were sprayed by the other gun.

Four runs were made as follows:

TABLE 11

First Gun Second Gun 1 NiCrAlY A1203 2 CoNiCkAlY A1203 3 NiCrAlY ZrOVY203 4 CoNiCrAlY ZrOVY203 1 RD- 19. 4 -11 As a measure of preparation for forming the plasma spray deposits, the substrates were first heated in the plasma f lame to about 9000C and the substrate surface was reverse transferred arc cleaned prior to commencing the 5 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 Ren6 80 coupons having. configurations as illustrated in Figure 2.

These coupons were about 1/2 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 11500C for 50 minutes and in room air for 10 minutes. Weight change 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 A1203 is preferred to the Zr020Y203 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 A1203 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 -itructures 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 L RD-19, 431 properties attainable with the combination of ingredients used.

In the above example, the coatings were prepared as thermal barrier coatings. The coatings containing the 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 10 conductivity of NiCrAlY.

EXAMPT,r P: High Strength, Low Density, Free-Standing Microlaminated Composites of Ren6 80/A1203 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 Ren6 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 Ren6 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 Ren& 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 of 45 was used to form tubes of each composition. 30 (2) A second set of tubes having Ren6 80/A1203 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 A RD-19. 431 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 Ren& 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 depolits 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 % A1203 15 and 35 volume % R-80. The structure of Figure 4 is formed from a composition of 50 volume % of A1203 and 50 volume percent R- 80. The structure of Figure 5 is formed from a composition having 35 volume % A1203 and 65 volume percent Ren6 80. 20 The ReM 80 powder employed in these experiments was a 400 mesh powder having an approximate average particle size of about 20 microns. The alloy Ren6 80 is a commercially available alloy which has a composition by weight of 9.5 % cobalt, 14.0 % chromium, 3.0 % aluminum, 5.0 % 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 hive associated with the improvement in properties RD-19. 431 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.

TABLE III

Properties of Microlaminated Composite Tubes of Rene 80/Al 2 0 3 i Density (grn/cm3 Average Based DCP Elastic on Expansion Modulut 3-P &nd IPQ-Fmd Conditions Composition From Calculated Calculated Measured Coefficient Electrical Strength at Rate - Gum Image Antlytis, Item Pc- from Imago As Dep/ 23 - 1250C Resistivity As Deposited Heat Treated. Room Temp.

(Reo;O W^%) (4 (Rcnc'W.A03) feed rate Antlytia HT (X 10 -6 M () X 105 RIO pd) kto W.20 45 68.931.1 733 626 6.73/6.81 13.0 281 37A 433 219 0:33 4? 53.6.46.4 4.70 621 6321630 113 408 40.6 334 114 45:33 14r 39.1.40.9 6.70 6AS 4P 402.393 6.07 5.66 92 90.50 tee 59.4..40.6 6.07 6.46 35.0 43 2U70.8 5.44 6.22 35.65 low 34.1:65.9 SA4 5.40 43 17.7 823 4.81 4.71 0 llcat Treatment: 2 hr at 125M In Ar 1 C3N 1 :I 1 1 1 - 17 RD-19. 431 The compositions of the deposits formed 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 Ren6 80/A1203 using the 100 gun angle, the Ren6 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 treatment 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 resistivities increase with increasing A1203 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 Ren6 80/A1203 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:

i lc - 18 TABLE IV

Rn-19,431 Tensile Test Properties of Microlaminated Ren6 80/A1203 Plates Specimens heat treated 2 hr., 1250% Ar except as noted Aim v/o Composition Test Temp. 0.2% YS UTS Ren6 80 A1203 (OC) (ksi) (ksi) R/A 20 RT 110.7 0 560 107.5 0 710 113.4 0 860 88.1 88.4 Small 1010 35.5 36.3 Small 25 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 35 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 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 50 50 RT 71.5 0 560 66.0 0 710 No data 860 64.8 64.8 Small 1010 36.7 0 RT 140 195 17.0 710 110 16t22.0 1010 30 40 10.0 Specimens not heat treated Representative data from previous studies 1 - 19 RD-1 9. 4 31 As is evident from the data included in the Table, the volume % ratios sought in preparing compositions were 8020; 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 Ren6 80 would be 100%. The ratios listed in the Table were deposited using powder keed volume ratios as set forth. Sheet tensile specimens were cut from the plates. The results of the tests from room temperature to 101CC are summarized in Table IV. These data can be compared with representative tensile data for rapidly solidified plasma deposited Ren6 80 as set forth next to the 100% Ren6 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 Ren6 80 sample. The trend is for tensile strength to decrease with increasing A1203 content. It should be noted that the 3 point bend strength values for the Ren6 80 A1203 microlaminated specimens of Table III are significantly higher than the axial values. In addition, the axial tensilestrengths of the microlaminated composites are almost equal to the rapidly solidified plasma deposited Ren6 80 at 10100C. 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 at low density, and accordingly to have a high strength to weight ratio. Also, it is evident that the 30. density of the-material can be tailored to a desired value by changing the properties of the Ingredients used.

- 20 RD- 19. 4 31 EXAMPLE 3: Free-standing Microlaminated Composites of Invar:/A1203 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.

The apparatus and methods of the previous examples were again employed. Using these methods and apparatus, the properties of microlaminated composites of Invar/A1203 were 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/A1203 composite 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.

1.

TABLE V

Properties of Microlaminated Composite Plates of Invar/Al 2 0 3 1 Aim W/0 3 Average Elastic CompoititIon Density (gm/cm Based Expansion Modulus At Room on Composition Temp.

Poced from Calculated Calculated Coefficient Electrical kal) Rate linqcA rromPo from Image Measured 251 to 5001C Redstivity As Deposited Heat Treated 3-Point Bend (1,%# 3) (Iww^03) Feed Rate Ana"t As Dep/Ht (a 10-61IC) (9b-cm) X 106 Psi) X 106 Pd Strength 65:33 SIA:48A 6.39 6.04 6111 9.2 246 29.8 63.1 31A ".55 3@jd%32 5.99 SAS 5.521 8.0 445 313 32.7 64.1 24A 35:0 21.9.78.1 $in 4AS 4.8414.74 83 1641 1W (Hen) 8.0 8.0 1 IIA (65 85 kol) YS - (40 - 60 ltd) Red Treatment, 2 br 12M Ar 1 1 1 1 1 A - 22 RD-1 9. 4 31 The microlaminated sample of 35 Invar/65 A1203 formed on the plate was found to be extremely brittle and so brittle, in fact, that it could not be machined into a mechanical test specimen. From the Table V, it can be seen that the Invar content of these microraminated 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 Ren6 80 and A1203. 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/A1203 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 A1203 content.

A minimum in expansion coefficient at a volume ratio of about 40% Invar/60% A1203 was indicated. The data obtained indicate that the microlaminated Invar/A1203 compositions can be identified with a thermal expansion coefficient approximating that of Invar.

From the data obtained from this evaluation of the microlaminated Invar/A1203 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.

1 R RD-1 9. 4 31 E IPLE 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 10 summarized in Table VI.

TABLE VI

Properties of Microlaminated Composite Plates of Cu/Al 20 3 Density (gm/cm 3 Average Expansion Abn Y/o Compoeition Composition from Calculated Calculated doefficient Electrical Elastic Modulus Based on Powder-Feed Image Analysis from Powder. ftom Image Measured 25 to ROWC Resistivity As Deposit W, Rate (OnAI203) (Cu:A03) Feed Rate Analysis As Dep. (X IT /C) (pn-cm) X 10 psi 65:35 61.138.7 %19 7.00 7.29 13.6 9 23.8 "-50 41.8:58.2 6.45 6.04 6.56 10.2 16 20.8 35.65 25.7..74.3 5.70 5.24 5.56 8.4 51 27.1 01 fflan) 8.96 16.5 1.67 16 1 tO 41.

1 :I 1 _A D 1 jb. A - 25 RD-1 9. R1 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 % A1203 5 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 A1203 content. The elastic modulus values reflect the A1203 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 twogun 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 corrosion 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 of advanced 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 advantages are the RD-19, 431 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 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. What was achieved by the examples recited above was a simultaneous bombardment of the substrate with splatters of both materials so that the two phases were intermingled 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 performed, as represented by Examples referred to above, demonstrated the potential of forming free standing composites and coatiii-g 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 obtainedIndicate the potential of this system for tailoring 4 is RD-1 9. 4 31 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, elastic modulus values of the composite can beincreased 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.

1 Rr)-1 9. 4 31 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.

1 1

Claims

CLAIMS:

1. The method of forming a microlaminated structure having interlaminar reinforcements which comprises, providing a first plasma gun adapted to plasma spray deposit a first material, providing a second plasma gun adapted to plasma spray deposit a second material, directing the plasma spray from both the first and second plasma guns onto the same area of a receiving surface, thereby to cause substantial swirling of the layers of deposit onto said surface and to cause thereby interlayer reinforcing strands to be formed in said deposit.

2. A microlaminated structure, said structure being made up of solidified intermixed splats of a first and of a second material, said splats having a swirly configuration whereby interlayer reinforcing strands extend from one splat to another of said structure.

3. The method or structure of claim 1 or 2 in which the first material is a metal.

4. - The method or structure of claim 1 or 2 in which the first and second materials are metals.

5. The method or structure of claim 1 or 2 in which the first and second materials are metals of distinctly different properties.

6. The method or structure of claim 1 or 2 in which the second material is a ceramic.

1 8. The method or structure of claim 1 or 4 in which the ratios of the materials is between 10:90 and 90:10.

9. The method or structure of claim 1 or 4 in which the ratios of materials is between 20:80 and 80:20.

10. A method of forming a microlaminated structure substantially as hereinbefore described with reference to Figure 1 or to Examples 1 to 4.

11. A microlaminated structure substantially as hereinbefore described optionally with reference to Figures 3 to 5 of the accompanying drawings.

12. Apparatus for forming a microlaminated structure substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings.

Published 1991 at 7he Patent Office, State House, 66171 HighHolborn. London WC1 R 47P. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys. Newport. NP1 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.