US3807996A

US3807996A - Carbon fiber reinforced nickel matrix composite having an intermediate layer of metal carbide

Info

Publication number: US3807996A
Application number: US00270260A
Authority: US
Inventors: R Sara
Original assignee: Union Carbide Corp
Current assignee: BP Corp North America Inc
Priority date: 1972-07-10
Filing date: 1972-07-10
Publication date: 1974-04-30
Anticipated expiration: 1991-04-30
Also published as: GB1371889A; FR2192193B1; IT989794B; DE2334218B2; FR2192193A1; DE2334218A1; JPS5224501B2; JPS4953119A

Abstract

Composite articles having a nickel base metal matrix reinforced with a plurality of high strength, high modulus carbon fibers having a thin, intermediate layer of a metal carbide disposed upon at least a portion of the fiber surfaces. Such composites are characterized by improved thermal cycling characteristics and are produced by coating a plurality of carbon fibers first with a thin, continuous layer of nickel, and then with a second thin, continuous overcoating of a metal capable of diffusing through the nickel coating and reacting with carbon to form a metal carbide; and then hot pressing the dual-coated fibers for a time and at a temperature and pressure sufficient to bond them together and diffuse at least a portion of the carbide-forming metal surface layer through the nickel undercoating and effect reaction between said carbide-forming metal and said carbon fibers to produce a metal carbide coating on at least a portion of the surface of the fibers.

Description

United States Patent [19] Sara [451 Apr. 30, 1974 [75] Inventor: Raymond Vincent Sara, North Olmsted, Ohio [73] Assignee: Union Carbide Corporation, New

York, NY.

22 Filed: July 10, 1972 211 App]. No.: 270,260

[52] US. Cl 75/204, 29/l83.5, 29/191.2, 29/419, 75/D1G. 1, 75/212, 75/226, 117/71 R, 117/100 R, 1l7/D1G. 11, 204/37 [51] Int. Cl C22c l/04, B22f 3/14 [58] Field of Search 75/DIG. l, 212, 226, 204; 29/l83.5, 191.2, 419; 117/D1G. ll, 71 R,

[56] References Cited UNITED STATES PATENTS 3,622,283 ll/1971 Sara 29/l83.5

3,571,901 3/1971 Sara 29/419 3,553,820 l/l971 Sara 29/419 3,550,247 12/1970 Evans et a1. 29/419 3,476,604 ll/1969 Faber 75/212 X 3,443,301 5/1969 Basche et al 75/D1G. 1

3,535,093 lO/l970 Sara 75/212 X 3,098,723 7/1963 Micks 75/D1G. 1 3,047,383 7/1962 Slayter... 75/D1G. 1 2,548,897 4/1951 Kroll ll7/DIG. 11 2,093,390 9/1937 Wyckoff 117/DIG. 11

OTHER PUBLICATIONS Hanby, K. R. DMIC Review of Recent Developments.

Fiber Reinforced Metals. Batelle Memorial Inst., C0- lumbus, 1970. pp. 1-2.

DMIC Report S-30, Batelle Memorial Institute, Columbus, 1969. p. 5.

DMIC Report S-27, Batelle Memorial Institute, Columbus, 1969. abstract No. 42, pp. 24-25.

Primary ExaminerCarl D. Quarforth Assistant ExaminerR. E. Schafer Attorney, Agent, or FirmJohn S. Piscitello [57] ABSTRACT Composite articles having a nickel base metal matrix reinforced with a plurality of high strength, high modulus carbon fibers having a thin, intermediate layer of a metal carbide disposed upon at least a portion of the fiber surfaces. Such composites are characterized by improved thermal cycling characteristics and are produced by coating a plurality of carbon fibers first with a thin, continuous layer of nickel, and then with a second thin, continuous overcoating of a metal capable of diffusing through the nickel coating and reacting with carbon to form a metal carbide; and then hot pressing the dual-coated fibers for a time and at a temperature and pressure sufficient to bond them together and diffuse at least a portion of the carbide-forming metal surface layer through the nickel undercoating and effect reaction between said carbide-forming metal and said carbon fibers to produce a metal carbide coating on at least a portion of the surface of the fibers.

28 Claims, No Drawings CARBON FIBER REINFORCED NICKEL MATRIX COMPOSITE HAVING AN INTERMEDIATE LAYER OF METAL CARBIDE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to composite articles having a nickel base metal matrix reinforced with a plurality of high strength, high modulus carbon fibers having a thin, intermediate layer of a metal carbide disposed upon at least a portion of the fiber surfaces.

2. Description of the Prior Art As a result of the rapidly expanding growth of the aircraft, space and missile industries in recent years, a need was created for materials exhibiting a unique and extraordinary combination of physical properties. Thus, materials characterized by high strength and stiffness, and at the same time of light weight, were required for use in such applications as the fabrication of aircraft structures, re-entry vehicles, and space vehicles, as well as in the preparation of marine deepsubmergence pressure vessels and like structures. Existing technology was incapable of supplying such materials and the search to satisfy this need centered about the fabrication of composite articles.

One of the most promising materials suggested for use in composite form was high-strength, high-modulus carbon fibers, which were introduced into the market place at the very time this rapid growth in the aircraft. space and missile industries was occurring. Such fibers have long been incorporated into plastic matrices to produce composites having extraordinary highstrengthand high-modulus-to-density ratios, and more recently efforts have centered upon the preparation of composites having metal matrices.

Since nickel readily adheres to carbon and these two materials are light weight and essentially nonreactive with each other, the use of high strength, high modulus carbon fibers as a reinforcing agent for nickel in forming composites having high modulus-to-density ratios and high strength-to-density ratios has been suggested. Composites of this type, however, are generally employed in environments where they are subjected to wide ranges of temperatures, and, because of marked differences between the coefficients of thermal expansion of carbon and nickel, such composites have been found to possess poor thermal cycling characteristics. Under such conditions, these composites undergo extensive, irreversible dimensional distortions in a direction perpendicular to the fiber axis which is accompanied by the formation of considerable porosity and a significant degradation of the mechanical properties of the composite, such as Youngs modulus and flexural strength. Thus, for example, when repeatedly heated from room temperature to 500 C., composites containing 46 percent by volume of carbon fiber and 54 percent by volume of nickel were found to increase in porosity by 37 percent, while the Youngs modulus and flexural strength of the composites decreased from 43 X 10 psi. and 140 X l psi. to 23 X 10 psi. and X 10 psi., respectively.

The irreversible dimensional deformation of a material induced by thermal cycling is known as ratcheting. It is believed that this effect, and the disintegration of composite properties which accompany it in carbon fiber-nickel matrix composites, is a result of shear stresses which develop at the interface of the carbon fibers and the matrix of the composite as it is heated to high temperatures and subsequently cooled.

Thus, as the composite temperature increases as it is heated, the interfacial bond strength between the carbon fibers and the nickel matrix also increases while, at the same time, the nickel matrix expands at a greater rate than do the fibers. Full expansion of the matrix at the fiber interface is constrained, however, by the interfacial bond strength of these materials. This causes a compressive stress to be exerted on the matrix and a tensile stress to be exerted on the fibers. Ultimately, the compressive stress on the matrix is relieved by plastic flow of the matrix in a direction perpendicular to the fiber axis, resulting in distortion of the composite dimensions.

When the heating cycle is reversed and the composite is cooled from an elevated temperature, the stresses exerted on the matrix and fibers are reversed, i.e., the fibers are subjected to a compressive stress and a tensile stress is exerted on the matrix as it attempts to contract at a faster rate than the interfacial bond strength with the fiber will allow. At the same time, however, the interfacial bond strength of the fibers and matrix is gradually reduced by the cooling and, eventually, declines to a point where it is exceeded by the tensile stress exerted on the matrix. This causes slippage of the matrix and a permanent weakening of the bonding between the fibers and the matrix, which seriously degrades the mechanical properties of the composite.

SUMMARY OF THE INVENTION ln accordance with the instant invention, it has now been discovered that the interfacial bonding characteristics of carbon fiber-nickel base metal matrix composites can be substantially improved by providing a thin, intermediate layer of a metal carbide over at least a portion of the interface between the surface of the fibers and the nickel base matrix. As a result of this improved interfacial bonding between the fibers and matrix, the composites are characterized by improved thermal cycling characteristics and may be repeatedly cycled over a wide range of temperatures without undergoing the ratcheting effect and mechanical property degradation heretofore characteristic of carbon fibernickel matrix composites. Thus, even after being thermally cycled 500 times over a temperature range of from to 500 C., no ratcheting is observed in composites prepared in accordance with the present invention.

Any metal carbide which can be formed by the reaction of carbon and a metal capable of reacting with carbon to produce a metal carbide can be employed to improve the interfacial bonding characteristics of carbon fiber-nickel base metal matrix composites. Coatings of this type are provided at the interface between the surface of the carbon fibers and the nickel base metal matrix according to the invention by coating a plurality of carbon fibers first with a thin, continuous layer of nickel, and then with a second thin, continuous overcoating of a metal capable of diffusing through the nickel coating and reacting with carbon to form a metal carbide; and then hot pressing the dual-coated fibers for a time and at a temperature and pressure sufficient to bond them together and diffuse at least a portion of the carbide-forming metal surface layer through the nickel undercoating and effect reaction between said carbide-forming metal and said carbon fibers to produce a metal carbide coating on at least a portion of the surface of the fibers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A thin, continuous coating of nickel can be applied to the carbon fibers by a variety of known techniques, including electrodeposition from an aqueous salt bath, electro-less deposition, thermal decomposition of an appropriate metal carbonyl or halide, and sputtering. Electrodeposition from an aqueous salt bath provides a uniform, tenaciously bonded coating and is the preferred means of applying nickel to the fibers according to the present invention. In order to allow for subsequent diffusion of the exterior coating through the nickel coating, the nickel coating should not be applied in a thickness in excess of bout 5 microns. Most preferably, it is applied in a thickness of from about 1 micron to about 3 microns.

After the carbon fibers have been coated with nickel, they are coated with a second thin, continuous layer of a metal capable of diffusing through the nickel coating and reacting with carbon to form a metal carbide. The second coating is applied to the nickel coating by the same techniques employed to deposit the nickel coating, e.g., electrodeposition from an aqueous salt bath, electroless deposition, thermal decomposition of an appropriate metal carbonyl or halide, and sputtering. While the nickle coating should be applied in a thickness of at least about 1 micron, the carbide-forming metal may be applied in somewhat thinner coats, e.g., up to about 5,000 A. In order to ensure that sufficient carbide-forming metal is present to diffuse through the nickel coating and react with the carbon fibers to form an amount of metal carbide which will effectively bond the metal matrix to the carbon fibers, the carbideforming metal should be applied in a thickness of at least 50 A. However, in order to prevent excessive degradation of the carbon fibers, the thickness of the carbide-forming metal coating should not exceed 5,000 A. Preferably, the carbide-forming metal is present in a thickness of from about 500 A to about 2,000 A.

Among the metals capable of diffusing through nickel and reacting with carbon to form a metal carbide which can be employed to improve the interfacial bonding characteristics and thermal cycling characteristics of carbon fiber-nickel metal matrix composites according to the present invention are such metals as titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and iron. The most preferred metals are chromium and iron.

After the carbide-forming metal has been applied on the nickel coated carbon fibers as aforesaid, the dualcoated fibers are hot pressed, preferably in side-by-side or parallel manner, for a time and at a temperature and pressure sufficient to bond them together and diffuse at least a portion of the carbide-forming metal surface layer through the nickel undercoating and effect reaction between said carbide-forming metal and said carbon fibers to produce a metal carbide coating on at least a portion of the surface of the fibers. Hot pressing is conducted in a non-oxidizing atmosphere, e.g., in an inert atmosphere or under vacuum. By an inert atmosphere is meant an atmosphere which does not react with nickel or the carbide-forming metal under the reaction conditions employed during hot pressing such as nitrogen, argon, xenon, helium and the like.

In order to diffuse the carbide-forming metal through the nickel undercoating and produce a metal carbide coating on the fibers, it is necessary to hot press the coated fibers at a temperature which is sufficiently elevated to cause sintering of both the nickel underlyer and carbide-forming metal overcoating, as well as sufficiently elevated to effect reaction between the carbide-forming metal which diffuses through the nickel undercoating and the carbon fibers. The pressure applied must be sufficient to bond the sintered metal coated fibers together into a composite. Unnecessary severe processing conditions should be avoided during hot pressing as this may cause physical and chemical damage to the fibers and weakening of the composite. For example, excessive temperatures may cause dissolution of the fibers into the nickel undercoating, while excessive pressure may result in fiber rupture. For this reason, it is preferred to use the minimum processing conditions necessary to diffuse the carbide-forming metal through the nickel undercoating effect reaction between the carbide-forming metal which diffuses through the nickel and the carbon fibers, and effectively bond the coated fibers and attain maximum densification, i.e., to eliminate virtually all porosity and produce a non-porous article.

The temperature at which hot pressing is effected will depend upon the sintering temperature of the carbideforming metal employed, and the temperature at which such metal reacts with carbon to form a metal carbide. The pressure required will, of course, depend upon the temperature employed, with higher pressures being required at lower temperatures. Generally, hot pressing can be readily effected at temperatures of from about 700 C. to about 1,300 C., preferably from about 800 C. to about l,l00 C. Pressures in excess of 500 psi. are usually employed, with pressures of from about 1,500 psi. to about 2,500 psi. being preferred. To avoid fiber rupture during hot pressing, it is preferred not to use pressures in excess of 4,500 psi.

Hot pressing should be continued for a time sufficient to diffuse the carbide-forming metal through the nickel undercoating, effect reaction between the carbideforming metal which diffuses through the nickel and the carbon fibers, and effectively bond the coated fibers and attain maximum densification. The time required to accomplish this for any given metal will depend, of course, upon the temperature and pressure employed. Under most conditions, hot pressing can be completed within from about 2 minutes to about minutes, usually within from about 30 minutes to about 60 minutes.

Since the entire coating of carbide-forming metal which is deposited on the intermediate nickel layer does not ordinarily fully diffuse through said layer during hot pressing, a nickel base matrix composed of nickel and said carbide-forming metal results from such processing. lf excessive carbide-forming metal has been deposited on the nickel layer, a thin layer of undiffused metal may even remain on the surface of the nickel base metal matrix after hot pressing.

As previously indicated, the metal carbide coating which forms at the interface between the surface of the carbon fibers and the nickel base matrix according to the present invention serves to improve the interfacial bonding characteristics and thermal cycling characteristics of the resulting composite. Because this metal carbide layer is formed at relatively low temperatures in the presence of an intermediate nickel layer which serves as a diluent for the reaction between the carbide-forming metal and the carbon fibers, excessive degradation of the fibers is thereby avoided.

High modulus, high strength carbon fibers suitable for use in the instant invention can be prepared as described in U.S. Pat. No. 3,503,708 and 3,412,062.

The following examples are set forth for purposes of illustration so that those skilled in the art may better understand this invention, and it should be understood that they are not to be construed as limiting this invention in any manner. The term carbon as used throughout this specification includes all forms of the material, both graphitic and non-graphitic. The term nickel base metal matrix includes matrices containing at least 50 percent by weight of nickel.

EXAMPLE 1 A two ply graphite yarn having 720 filaments per ply wherein the filaments are characterized by an average Youngs modulus of 75 X psi. and an average tensile strength of 335 X 10 psi. was electroplated with nickel using a standard Watts plating solution. The fibers were passed between copper rollers which were positioned about two inches before a plating bath and connected to an electrical source whereby electrical contact was made with the fibers. The fibers were then passed into the plating bath where nickel was deposited on the fibers from a nickel anode. The aqueous electroplating solution employed contained 200 grams of Ni- SOhd 4 -6H O, 50 grams of NiCl 6H O and 30 grams of H 80 per liter of water. The solution temperature was maintained at 50 C., and a plating current of 2.5 amperes was employed. The residence time of the fibers in the bath was 14 minutes. After passing through the electroplating solution, the yarn was washed by passing it through hot water, dried at 200 C., and stored on take-up spools. Metallographic examination of the resultant nickel coated fibers showed that all monofilaments had a coating of nickel thereon, and that the coating thickness ranged from i to 3 microns.

The nickel clad fibers produced in this manner were than heated at a temperature of 800 C. in an atmosphere containing 85 volume percent argon and 15 volume percent hydrogen in order to clean the fibers and reduce any nickel oxide present. A second layer of chromium was then applied to the fibers in a manner similar to that described above using a lead anode and an aqueous plating bath containing 250 grams of H CrO and 2.5 grams of (SO per liter of water. The (80 was partially provided by Cr (SO,,) and partially by H 80 The plating solution was maintained at room temperature and a plating current of 7.5 amperes was employed. The residence time of the fibers in the bath was 1 1 minutes. After passing through the electroplating solution, the yarn was washed in hot water, dried at 200 C., and stored on take-up spools. Metallographic examination of the resultant chromium coated fibers showed that all monofilaments had a coating of chromium thereon and that the coating thickness ranged from 2,000 A to 4,000 A. The total weight of chromium deposited was about weight percent of the nickel coating.

The dual-coated fibers produced in this manner were then cut into approximately 1 inch lengths, aligned in a parallel manner in a graphite mold and hot pressed under vacuum (about 20 microns of mercury pressure) for 1 hour at a temperature of 1,050" C. and a pressure of about 3,000 psi. to form solid bars approximately one-inch long, one-eighth-inch wide, and onesixteenth-inch thick. Each specimen contained about coated fiber plys, or about 50 volume percent fibers and 50 volume percent metal. A portion of the chromium overlayer diffused through the nickel undercoating during the hot pressing and reacted with the carbon fibers to produce acoatin'g of chromium carbide at the interface between the fibers and the nickel matrix.

A number of the composites produced in this manner were treated with a 50 volume percent solution of hydrochloric acid in water to dissolve the nickel and unreacted chromium present on the fibers. Metallographic examination of the recovered fibers showed the presence of undulations on the surface of the fibers caused by the reaction of the fibers with the chromium to form chromium carbide.

The remaining composites were placed in a fused quartz ampoule. Air was evacuated from the ampoule, and the ampoule was then pressurized with argon to a pressure of about one-half atmosphere and sealed. The ampoule and its contents were then thermally cycled 500 times between and 500 C. At the end of this time, the composites were examined and found to exhibit no dimensional change as a result of the thermal cycling. Metallographic examination of the composites showed the matrix was still uniformly clad around the filaments. On the other hand, composites produced from nickel and identical fiber, in the same manner, but without the application of the chromium coating, had many separations and voids between the fibers and the matrix.

EXAMPLE 2 Nickel coated fibers produced and heat-treated as described in Example 1 were cut into approximately 5 inch lengths, clamped to an electrical lead and immersed in a plating bath where iron was deposited on the fibers from an iron node. The aqueous electroplating solution employed contained 350 grams of Fe(NH $0., per liter of water. The plating solution was maintained at room temperature and a plating current of 5 amperes was employed. The residence time of the fibers in the bath was 17 seconds. At the end of this time, the yarn was then removed from the bath, washed in hot water and dried at 200 C. Metallographic examination of the resultant iron coated fibers showed that all monofilaments had a coating of iron thereon, and that the coating thickness ranged from 2,000 A to 4,000 A. The total weight of iron deposited was about 20 weight percent of the nickel coating.

The dual-coated fibers were then formed into composites of the same size and shape as described in EX- ample l by employing the same procedure described therein. As in the composites produced in accordance with Example 1, a portion of the o'verlayer, in this case iron, diffused through the nickel undercoating during hot pressing and reacted with the carbon fibers to produce a coating of iron carbide at the interface between the fibers and the nickel matrix.

As in Example 1, a number of composites produced in this manner were treated with a 50 volume percent solution of hydrochloric acid in water to dissolve the unreacted metals present on the fibers. Again, metallographic examination of the recovered fibers showed the presence of undulations on the surface of the fibers, in this case caused by the reaction of the fibers with the iron to form iron carbide.

The remaining composites were then thermally cycled in the same manner as the composites in Example 1. As in the composites produced in accordance with Example 1, no dimensional change was found to occur as a result of the thermal cycling. Again, metallographic examination of the composites showed the matrix was still uniformly clad around the filaments.

Composites produced in the above manner are extremely useful as materials of construction for subsonic and supersonic aricraft, space system components and various propulsion devices.

it will be readily apparent to those skilled in the art that the composite articles of the instant invention may be fabricated to meet various design requirements as to size, shape, stress relationships, and the like. Thus, any shape in which the metallized carbon fibers are wound or stacked in parallel relationship can be provided. For example, such fibers can be wound on a mandrel and hot pressed to produce a coiled composite, or laid out in parallel manner and compressed to produce plates of various sizes and shapes. In addition, where more isotropic physical properties are desired, laminates can be prepared in which the metallized fibers are arranged in layers wherein the fibers of each layer remain in parallel relationship but are in non-parallel relationship to the fibers of the adjacent layer.

I claim:

1. A process for producing a composite article having a nickel base metal matrix reinforced with a plurality of high strength, high modulus carbon fibers having a thin, intermediate layer of a metal carbide disposed upon at least a portion of the fiber surfaces which comprises coating a plurality of carbon fibers first with a thin, continuous layer of nickel, and then with a second thin, continuous overcoating of a metal capable of diffusing through the nickel coating and reacting with carbon to form a metal carbide; and then, hot pressing the dual-coated fibers in a non-oxidizing atmosphere for a time and at a temperature and pressure sufficient to bond them together and diffuse at least a portion of the carbide-forming metal surface layer through the nickel undercoating and effect reaction between said carbideforming metal and said carbon fibers to produce a metal carbide coating on at least a portion of the surface of the fibers.

2. A process in claim 1 wherein the nickel coating is applied in a thickness of no more than 5 microns and the carbideforming metal is applied in a thickness of from 50 A to 5,000 A.

3. A process as in claim 2 wherein the carbideforming metal is chromium.

4. A process as in claim 2 wherein the carbideforming metal is iron.

5. A process as in claim 1 wherein the nickel coating is applied in a thickness of from 1 micron to 3 microns and the carbide-forming metal is applied in a thickness of from 500 A to 2,000 A.

6. A process as in claim 5 wherein the carbideforming metal is chromium.

7. A process as in claim 5 wherein the carbideforming metal is iron.

8. A process as in claim 2 wherein the nickel and carbide-forming metal coatings are applied by electrodeposition from an aqueous salt bath.

9. A process as in claim 8 wherein the carbideforming metal is chromium.

10. A process as in claim 8 wherein the carbideforming metal is iron.

11. A process as in claim 5 wherein the nickel and carbide-forming metal coatings are applied by electrodeposition from an aqueous salt bath.

12. A process as in claim 11 wherein the carbideforming metal is chromium.

13. A process as in claim 11 wherein the carbideforming metal is chromium.

14. A process as in claim 1 wherein hot pressing is effected at a temperature of from 700 to 1,300 C. and at a pressure of from 500 psi. to 4,500 psi.

15. A process as in claim 14 wherein the carbideforming metal is chromium.

16. A process as in claim 14 wherein the carbideforming metal is iron.

17. A process as in claim 2 wherein hot pressing is effcted at a temperature of from effected 700 to l,300 C. and at a pressure of from 500 psi. to 4,500

psi.

18. A process as in claim 17 wherein the carbideforming metal is chromium.

19. A process as in claim 17 wherein the carbideforming metal is iron.

20. A process as in claim 5 wherein hot pressing is effected at a temperature of from 800 to 1,l00 C. and at a pressure of from 1,500 psi. to 2,500 psi.

21. A process as in claim 20 wherein the carbideforming metal is chromium.

22. A process as in claim 20 wherein the carbideforming metal is iron.

23. A process as in claim 8 wherein hot pressing is effected at a temperature of from 800 to l,l00 C. and at a pressure of from 1,500 psi. to 2,500 psi.

24. A process as in claim 23 wherein the carbideforming metal is chromium.

25. A process as in claim 23 wherein the carbideforming metal is iron.

26. A process as in claim 11 wherein hot pressing is effected at a temperature of from 800 to 1,100 C. and at a pressure of from 1,500 psi. to 2,500 psi.

27. A process as in claim 26 wherein the carbideforming metal is chromium.

28. A process as in claim 2 wherein the carbideforming metal is iron.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 3 Issue Date April 1 1974 mventorgg) Raymond Vincent Sara It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r. Column 3 Cline "bout" should read "about-r; line 30 "nickle" should read --nickel-- Column 4, line 1, a comma should appear after "pressing"; line 7, "underlyer" should read --underlayer--; line 22, a comma should appear after "undercoating".

Column 5, line 33, "SOhd4-6 H20" should read -SO4-6 H2O--.

' Column 6, line 46, "node" should read -anode--; line 60,,

"EX-" should read --Ex Column 7, line 54, after "process" insert --as--.

Column 8, line 32, "effcted" should read --effected-- and the word "effected" Where it presently appears should be deleted.

Signed and sealed this 17th day of September 1974.

(SEAL) Anttest:

MCCOY GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 Issue Date April 30, 197

memrb Raymond Vincent Sara It is certified that error appears in the above-identified potent and that said Letters Patent are hereby corrected as shown below:

r- Column l "bout" should read "about"; line "nickle" should read --nickel--, I

Column 4, line 1, a comma should appear after "pressing"; line 7, "underlyer" should read --underlayer--; line 22, a comma should appear after "undercoating".

Column 5 line 33, "S0hd4-6 H20" should read "804-6 H2O- Column 6, line 46, "node" should read --anode-; line 60,

"EX-" should read --Ex- Column 7, line 54, after "process" insert --as--.

Column 8, line 32, "effcted" should read "effected" and the word "effected" where it presently appears should be deleted.

Signed and sealed this 17th day of September 1974,

(SEAL) Attestt MCCOY M. GIBSON JR. c. MARSHALL DANN Arresting Officer Commissioner of Patents

Claims

2. A process in claim 1 wherein the nickel coating is applied in a thickness of no more than 5 microns and the carbide-forming metal is applied in a thickness of from 50 A to 5,000 A.
3. A process as in claim 2 wherein the carbide-forming metal is chromium.
4. A process as in claim 2 wherein the carbide-forming metal is iron.
5. A process as in claim 1 wherein the nickel coating is applied in a thickness of from 1 micron to 3 microns and the carbide-forming metal is applied in a thickness of from 500 A to 2,000 A.
6. A process as in claim 5 wherein the carbide-forming metal is chromium.
7. A process as in claim 5 wherein the carbide-forming metal is iron.
8. A process as in claim 2 wherein the nickel and carbide-forming metal coatings are applied by electrodeposition from an aqueous salt bath.
9. A process as in claim 8 wherein the carbide-forming metal is chromium.
10. A process as in claim 8 wherein the carbide-forming metal is iron.
11. A process as in claim 5 wherein the nickel and carbide-forming metal coatings are applied by electrodeposition from an aqueous salt bath.
12. A process as in claim 11 wherein the carbide-forming metal is chromium.
13. A process as in claim 11 wherein the carbide-forming metal is chromium.
14. A process as in claim 1 wherein hot pressing is effected at a temperature of from 700* to 1,300* C. and at a pressure of from 500 psi. to 4,500 psi.
15. A process as in claim 14 wherein the carbide-forming metal is chromium.
16. A process as in claim 14 wherein the carbide-forming metal is iron.
17. A process as in claim 2 wherein hot pressing is effcted at a temperature of from effected 700* to 1,300* C. and at a pressure of from 500 psi. to 4,500 psi.
18. A process as in claim 17 wherein the carbide-forming metal is chromium.
19. A process as in claim 17 wHerein the carbide-forming metal is iron.
20. A process as in claim 5 wherein hot pressing is effected at a temperature of from 800* to 1,100* C. and at a pressure of from 1,500 psi. to 2,500 psi.
21. A process as in claim 20 wherein the carbide-forming metal is chromium.
22. A process as in claim 20 wherein the carbide-forming metal is iron.
23. A process as in claim 8 wherein hot pressing is effected at a temperature of from 800* to 1,100* C. and at a pressure of from 1,500 psi. to 2,500 psi.
24. A process as in claim 23 wherein the carbide-forming metal is chromium.
25. A process as in claim 23 wherein the carbide-forming metal is iron.
26. A process as in claim 11 wherein hot pressing is effected at a temperature of from 800* to 1,100* C. and at a pressure of from 1,500 psi. to 2,500 psi.
27. A process as in claim 26 wherein the carbide-forming metal is chromium.
28. A process as in claim 2 wherein the carbide-forming metal is iron.