METHOD FOR PRODUCTION OF CERMETS OF ABRASIVE MATERIALS

Abstract: Method and apparatus for, and product of, formation of a matrix consisting of a metal binder and abrasive particles, using an intermediate coating on the abrasive particles and application of shock waves of controlled magnitude and direction to promote chemical bonding between metal binder, intermediate coating and abrasive particles to form a unitary, hard aggregate.

Description: - 1- METHOD FOR PRODUCTION OF CERMETS OF ABRASIVE MATERIALS Field of the. Invention. This invention relates to method and apparatus for incorporating a metal or metals as part of a binder or matrix for abrasive material particles such as diamond, boron nitride, silicon ( 5) carbide and the like. Background of the Invention. Powders or granules of abrasive particles such as diamond, boron nitride, boron carbide, silicon nitride, silicon carbide and tungsten carbide have a variety of industrial uses in machine tool (10) tips, wire drawing dies, precision abrasive equipment, high temperature- and wear-resistant coatings and many other areas. These particles coalesce only with difficulty, in the absence of high temperatures and pressures, and an intermediate material might be used as a binder or matrix to bind these particles together at (15) moderate temperatures and pressures. Preferably, the binder material should immobilize the powder particles at the temperatures associated with the contemplated abrasive uses. The abrasive particles and binder materials are often "bonded" together by a combination of heating and static pressing to produce a bound (20) mixture. Semenov, Pozdnyakov, Lapshina,and Ioffe, in Sov. Phys. - Doklady Y_[ 812(1967), have studied adhesive interaction of diamonds with metals(Pt, Ni, Zr, Cu, Ag, Mo, Ta, Fe and Co) at a vacuum of -5 -4 10 - 10 Torr pressure at temperatures substantially below ( 5) the adhesive activation temperature. The diamond and metal specimens were degassed, then statically pressed together at a specified temperature for a specified time period. An adhesion coefficient(proportional to the load required to pull the specimens apart) was found to increase linearly with the "curing" temperature (10) for most metals studied. Some metals, such as Zr, manifested significant adhesion coefficients at temperatures as low as T = 750°C; but other metals, such as Ta and Mo, showed little or no adhesion at temperatures as high as T = 900-1100°.. The metals tested fall naturally into two groups: (1) metals for which adhesion (15) is significant at low temperatures(T-__ 750°C), with a relatively high linear increase in adhesion coefficient witn increasing temperature; and (2) metals for which adhesion is either feeble or non-existent for temperatures as high as T = 1100°C, and for which the linear increase in adhesion coefficient with increasing (2C) temperature is either zero or relatively low. Semenov et al have also reported on a study of eutectic melting of iron, cobalt and nickel in stress-loaded contact with diamond and graphite. The eutectic formation temperatures were found to be T = 1150-1200°C(Fe), T = 1300-1335°C(Co) and T = (25) 1318°C(Ni); the nickel eutectic formation temperature is nearly as high as the melt temperature for nickel. These authors note that, where eutectic mixes of diamond and such metals are used for achining and grinding, the melting point temperature of the metal-diamond eutectic can be reached in such activities, wnich will certainly degrade or disable the eutectic mix. Methods to produce sintered diamonds, using eutectic alloys ( 5) of Co-Si or Co-Ti as a binder or matrix, are discussed by Ervens in "Development of processes for producing sintered diamond compacts", January 1981, published by Fried, Krupp GmbH, Krupp Forschungsinstitut. The methods used are static, requiring application of temperatures and pressures of T = 1300-1400°C and (10) p = 50-55 kbars, respectively, over time periods of the order of hours; and the resulting diamond volume is approximately 80 percent of the whole volume treated. Sintering of diamond powder at T = 1800-1900°C and p = 60-65 kbars for one hour, using matrix additives of B, Be and/or Si, (15) is discussed by Stromberg and ' Stephens in "Sintering of Diamond at 1800-1900°C and 60-65 kbar", Amer. Ceramic Soc. Bull..49 1030(1970) and in U.S.Patent 3,574,580 by the same workers. The boron additive was 0.5-1.0 urn diameter powder, and the resulting diamond sinter sizes were about 0.1 cm diameter. In some instances, (20) over 95 percent theoretical diamond density was obtained. Substantial portions of the sintered material remained in solution as diamond powder rather than being aggregated as αesired. Vander Sande, Uhlmann and Akeson, in "Improved Diamond Tool Life Through the Use of Coated Diamonds", Soc. of Manufacturing (25) Engrs. Publ. MR 85-308(1985), have briefly reviewed the cold press/sinter and hot press techniques for producing diamond powder/metal binder aggregates and have noted that two problems are extant with either approach: (1) distribution of the diamond in the resulting aggregate must be carefully controlled to optimize the tool life of the material; and (2) creation of a true chemical bond between diamond and metal binder is unlikely with such approaches. ( 5) These authors speculate on the use of diamonds coated with a metal carbide(Tι ' C, ZrC, HfC), with which the metal binder then reacts more easily to form a true chemical bond. Metals studied for the binder include Al, Si, Ni, Al-Cu-Mg, Al-Ni, Cr, Ni-Cr, Cr-Co, Al-Cu and Ni-Ti. The carbide-forming metal coatings were applied by tumble (10) plating, and the coated diamonds were bound into the metal matrix by hot pressing at temperatures T = 900-1100°C for periods of 5-60 minutes. Cylindrical samples as large as 1 cm in diameter have been formed in this manner. Application of hot pressing for extended periods(longer than 60 minutes) often degrades the bond strength. (15) Summary of the Invention. One object of the invention is to provide method and apparatus for binding abrasive powders or granules such as diamond, boron nitride and silicon carbide into a metal matrix for tool manufacturing and other uses. (20) Another object is to provide a unique material system that probably is not formable in any other manner. Other objects of the invention, and advantages thereof, will become clear by reference to the detailed description and the accompanying drawings. (25) To achieve these objects, the method invention in one embodiment may comprise the steps of: providing a powder or granules of predetermined abrasive particles, which may be diamond, boron nitride, silicon carbide or the like, of particle diameter ,-, substantially 1 μm or larger; providing a powder of a predetermined intermediate coating material, which may be Al, Ti, Zr, Hf, Ta or the like, of thickness substantially 0.01 n or greater, contiguous ( 5) with the abrasive powder or granules; blending the abrasive and coating materials to promote formation of a substantially uniform coating of the intermediate coating material on the surfaces of the abrasive powder or granules; providing a powder of a predetermined metal binder material, which may be Fe, Ni, V, Cr, Zr, Ti, Nb, Ta, (10) Co, w or Mo, of particle diameter substantially 1 μm or larger, of amount equal to 1-25 percent of the volume of the coated abrasive particles, with the binder metal powder being substantially uniformly dispersed among the coated abrasive particles; providing a flexible, air-tight container, with side walls, for the mixture of (15) abrasive/intermediate coating/metal binder and packing the mixture in a container so that the container is substantially filled with the mixture; imposing a vacuum of pressure no higher than 10 -5 Torr on the interior of the container; providing a predetermined amount of explosive in contact with and surrounding the exterior (20) side walls of the container; detonating the explosive to promote formation of a substantially radial, inward-directed shock wave in the mixture contained in the container interior; and allowing firm * bonds to form between refractory particles and intermediate coating particles and between intermediate coating particles and metal (25) binder particles. Detailed Description. If a means could be found for bonding powder or granules of abrasive particles, such as diamond, boron nitride, boron carbide, silicon nitride, silicon carbide, tungsten carbide or the like, to ( 5) certain tough metallic binder materials, such as Fe, Ni, V, Cr, Zr, Nb, Ta, Co, w or Mo, one could produce an excellent material for machine tools and other uses. This material would combine the abrasive characteristics of the "hard" material (diamond, etc.) with the general toughness of the metallic binder, producing possibly an (10) unsurpassed combination. Unfortunately, these metallic binders do not readily bind to the abrasive particles so that some means of promoting or enhancing such binding must be devised. The subject invention provides a means of promoting such binding by interposing a small amount of an intermediate binder metal(of coating thickness (15) substantially 0.01 μm or larger) between the abrasive powder or granules and the metal binder to provide a strong bond to each of these materials under appropriate temperature and pressure conditions. The intermediate coating metal may be powder or granules of pure or suitably alloyed Al(for BN or SiN only), Ti, Zr, (20) Hf, Ta or the like, positioned contiguous to the abrasive particles(of diameter substantially 30-70 um) by blending the two substances together to achieve a reasonably uniform deposit of the intermediate coating material on the surfaces of the abrasive particles. The abrasive particles, thus coated, are then placed in (25) a matrix of metal binder particles(of diameter substantially 1 um or larger) so that the volume of the coated abrasive particles is 75-99 percent of the mixture volume. The mixture is then dynamically -7- co pacted, using strong shock waves generated by detonation of an adjacent shaped explosive, to produce dynamic pressures of tne order of 150-500 kilooars and appropriate corresponding temperatures; for diamond and boron nitride, one should take care that the ( 5) temperatures produced by the shock waves «_to not exceed the phase transformation temperature . of the abrasive material; such temperatures are approximately T t = 110__» _. The intermediate coating material then reajcts with the canatiguous abrasive particles and metal binder material tss form strong* possibly chemical, bonds (10) that bind the three materials togetner .as a single substance. The intermediate coating matssrlal is present a small volume fraction of the resulting compound zm sloes not _s r__cϊa>bly vary the mechanical response of the solid compound sπs-a-vis the mechanical response of the solid coQapourasB consisting «__τ_Ty of abrasive particles (15) and metal binder matrix. The intermediate coating material! is deposited upon the surfaces of the abrasive particles by bleading, which may involve tumble plating of one material by the other for a period of a few minutes to one or more hours. Alternati ely, blending may involve (20) preparation of a mixture of the abrasive particles and an initial coating material such as TiH and heating tne mixture to approximately T = 6ϋ0°F to decompose ttie TiH 2 , dra*. off the resulting hydrogen gas and promote ini ia i_r_ d ng of the Ti to the surfaces of the abrasive particles as TiC or a similar compound. (25) p U re Ti in powder form may be mixed directly with the abrasive particles, but this carries an increased possibility of a fire or detonation of the Ti powder. -8- The blending, whether by tumble plating or by reaction at elevated temperature or by a combination thereof, of the intermediate coating material and the abrasive particles is, of course, necessary before the remainder of the procedure can be ( 5) carried out. However, subjecting the combined abrasive/intermediate coating/metal binder materials to shock waves by detonation of the adjacent explosive is the most important step in producing the final product. This combination is subjected to elevated temperatures and pressures by passage of the shock wave therethrough, for very short (10) time intervals; and this process may produce products that cannot be produced in any other manner. Although the preferred embodiments of the invention have been shown and described herein, modification and variation may be made without departing from the scope of the invention.

Claims: CLAIMS : 1. A method for formation of abrasive particles in powder or granule form bound in a matrix of a predetermined metal binder material, the method comprising the steps of: providing a powder or granules of the abrasive particles of particle diameter substantially 1 μm or larger; providing a powder of a predetermined intermediate coating material of amount sufficient to deposit on each abrasive particle a coating of thickness substantially 0.01 μm or larger; blending the abrasive particles and the intermediate coating particles together to promote formation of a substantially uniform coating of the intermediate coating particles on the abrasive particles; providing a powder of the metal binder material of particle diameter substantially 1 μm or larger, of volume substantially 1-25 percent of the volume of the coated abrasive particles, and mixing the coated abrasive particles together with the metal binder material; providing a rigid, hollow, airtight, substantially cylindrical container having side walls and end walls; placing the mixture of coated refractory material and metal binder material in the container interior so that substantially all the container volume is filled with the mixture; imposing a vacuum of substantially 10 Torr pressure on the container interior and sealing the container; providing an explosive surrounding and contiguous with the container exterior sidewalls, of amount sufficient to provide a shock wave pressure on the mixture contained in the container of 150-500 kilobars, when the explosive is detonated; detonating the explosive to promote formation of a substantially radial, inward-directed shock wave in the mixture; and allowing firm bonds between the abrasive particles and the intermediate coating material, and between the intermediate coating material and the metal binder material, to form in response to passage of the shock wave through the mixture. 2. The method of Claim 1, wherein the metal binder material is drawn from a class consisting of Fe, Ni, V, Cr, Zr, Ti, Nb, Ta, Co, w, and Mo. 3. The method of Claim 1, further including the steps of: choosing diamond or boron nitride as said abrasive particles; and limiting the amount of said explosive so that the temperatures produced in the abrasive particles in response to detonation of said explosive do not exceed the phase transformation temperature of the abrasive material. 4. The method of Claim 1, further including the step of drawing the abrasive particles from the class consisting of diamond, boron nitride, boron carbide, silicon nitride, silicon carbide and tungsten carbide. -11- 5. The method of Claim 1, further including the step of drawing the intermediate coating material from the class consisting of Al, Ti, Zr, Hf and Ta. 6. The method of Claim 1, wherein the step of blending the abrasive particles and the intermediate coating particles includes tumbling the particles together to promote formation of a substantially uniform thickness deposit of the intermediate coating particles on the surfaces of the abrasive particles. 7. The method of Claim 1, wherein the step of blending the abrasive particles and the intermediate coating particles includes •the steps of: choosing TiH as the intermediate coating material; mixing the particles together and elevating the temperature of the mixture to substantially T = 600°F; allowing the TiH to decompose and drawing off the hydrogen gas; and allowing the Ti to react with the surfaces of the adjacent abrasive particles. 8. A product produced by the process recited in Claim 1.

Inventors: CLINE CARL F, WILKINS MARK L, CLINE, CARL, F., WILKINS, MARK, L.
Applicants: CLINE CARL F, WILKINS MARK L, CLINE, CARL, F., WILKINS, MARK, L.
Application year: 1986
Main classification: B24D3
IPC codes: B24D3, C09K3