Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1979-04-05
1982-05-18
McCarthy, Helen M.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
75 05AB, 75213, 75214, 75224, 423440, 4285395, 501 93, B22F 100, C04B 3552, C22C 2900
Patent
active
043303323
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns a process for the preparation of an extrahard material based on metal carbides, the properties of which are essentially similar to that of tungsten carbide but that is substantially lighter than the latter.
This material can be used for the manufacturing of tools for the machining of metals and which have excellent properties of resistance to wear, shock and heat.
This material is represented by the formula Mo.sub.x W.sub.1-x C, wherein x is between 0.01 and 1, and presents, as has been established by X ray diffraction analysis, a hexagonal crystal structure identical with that of tungsten carbide WC.
Hence, it consists of a solid solution containing tungsten and molybdenum monocarbides WC and MoC.
BACKGROUND OF THE INVENTION
It is known that tungsten carbide WC is much used as an extrahard material, namely for the manufacturing of machining tools such as cemented carbide tools for cutting metals and drilling rocks and minerals. It has been established that some of the desirable properties of WC, such as for instance its resistance to rupture and to developing cracks under moderate stress are related, at least partly, to its hexagonal crystal structure. Further this carbide is very hard and resistant under hot conditions and its wettability by cementing bonding metals, such as Co, Ni and Fe, is excellent.
However tungsten is heavy and expensive and, for economical reasons, it is desirable to replace it by a lighter and more abundant metal having similar properties. Molybdenum is one such metal: indeed, molybdenum monocarbide MoC has a hexagonal crystal structure identical with that of WC and is also very hard. Unfortunately, it is not stable above about 1200.degree. C. (whereas WC retains its strength to temperatures up to about 2700.degree. C.) which prevents it from being used in all applications suited to WC.
It has been shown, however that solid solutions of tungsten and molybdenum monocarbides, that is materials of the formula Mo.sub.x W.sub.1-x C defined hereinabove, possess excellent physical properties which practically resemble those of WC, even with proportions of the molybdenum carbide as low as 1%. Such materials are therefore much advantageous, as compared to pure WC, with regard to lightness and price since the density of MoC is only 9 (as compared with 15.7 for WC) and molybdenum is a relatively abundant and cheap metal. Further, the heat resistance of the solid solution and decomposition temperature thereof, in between that of MoC and WC, is directly related to the magnitude of the W/Mo ratio. However, in order to exploit these advantages, the method of manufacturing such solid solution should be also economical.
There already exists some methods to fabricate such solid solutions or, more specifically, such solid solutions with, in addition, significant proportions of iron-group metals such as Co, Ni and Fe. It has indeed been found that such metals promote the formation of materials consisting of carbides of hexagonal structure and of the formula Mo.sub.x W.sub.1-x C wherein x is the same as in the above-given definition.
Thus, there was obtained a hexagonal carbide of formula Mo.sub.0.44 W.sub.0.56 C in admixture with cobalt by heating together WC, Mo.sub.2 C, and C with 4.8% of Co at 2000.degree. C. (Z. Anorg. Chem. 262 (1950), 212-217). In this respect, the Applicant has found that when mixtures of compressed powders containing WC, Mo and C or W, Mo and C were reacted in the presence of 2.5-10% Co by heating 4 hrs to 1200.degree.-2000.degree. C. (the temperature being dependent on the W/Mo ratio) under an inert atmosphere, there were also obtained materials containing mainly, as the carbide phase, Mo.sub.x W.sub.1-x C in which 0<x<0.8.
According to another method, mixtures of sintered powders containing, in atom-percent, about 41% Mo, 57% C and 2% Co were fused together with variable proportions of WC and the product was annealed 300 hrs at 1200.degree. C. under 10.sup.-6 Torr. There was thus obtained a series of materials
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Ekemar Carl S. G.
Haglund Bengt O.
Schachner Herbert
Battelle (Memorial Institute)
McCarthy Helen M.
Ross Karl F.
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