Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1981-07-20
1983-11-29
Hunt, Brooks H.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
419 14, C22C 2900, C22C 110
Patent
active
044179227
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates to sintered hard metals, which are mixed carbides of metals selected from Groups IV to VI of the Periodic Table of Elements and possibly other metals, in conjunction with metals or alloys of the iron group. The extreme hardness and wear resistance of such products make them very suitable for use as tools or tool tips, for use in machine tools, and for dies and components generally, where wear-resistance is essential.
Modern sintered hard metals, such as are used for the machining of materials producing long chips, consist of tungsten carbide, WC, titanium carbide, TiC, tantalum carbide, TaC, or the mixed carbide of tantalum and niobium, (Ta,Nb)C, with cobalt as the customary iron group metal or alloy as a binder. For the machining of materials producing short chips, the classical cobalt-bound tungsten carbide hard metals, i.e. WC-Co, are used, often with small additions, e.g. about 0.5%-3%. of other carbides, such as TiC, TaC, NbC or VC.
Owing to the increasing cost of tungsten, replacements for tungsten carbide in hard metals have been investigated, leading to the development of hard metals free from or low in tungsten, such as those based on (Ti,Mo)C, Ti(C,N) or (Ti,Mo)(C,N) which developments still continue .
As a result of development in other directions, the WC content, constituting the hexagonal phase of hard metals, has been partially replaced by isomorphous phases, such as MoC, Mo(C,N) and (MoW)(C,N), while the cubic phase, usually containing TiC, TaC and/or NbC, has been partially replaced by HfC, VC and the corresponding mixed crystals. Depending on the production and sintering conditions employed, the cubic phase contains variable quantities of WC in solid solution.
Just as attempts have been made to replace tungsten carbide in hard metals, so has appeared the parallel necessity for a significant substitution of TaC, which is commonly a constituent of most sintered hard metals. The main reason for this need is that high Ta ores, in contrast to high Nb ores, are relatively scarce and, furthermore, Ta metal has latterly found greatly increasing use in the electronics industry. Developments brought about by the increasing scarcity and expensiveness of Ta, and hence of TaC also, have found that up to 50% of the TaC can be replaced by the lighter and cheaper NbC. (As is well known, Nb is 20 times as plentiful in the earth's crust as Ta). A total or partial replacement of TaC by HfC was also found possible and led to hard metals of outstanding properties.
However, at that time, the scarcity and resulting high prices of Hf and HfC precluded a broad introduction of this development. A certain break-through has come about recently, as a result of the growing zirconium industry, which has required an enforced separation of Hf and the consequent need to separate zirconium and hafnium from one another and from the ores which commonly contain them both. European and American research workers have established that niobium and hafnium carbide mixed crystals, (Nb,Hf)C, can not only replace TaC, but can even lead to hard metals of 20%-30% increased performance. (As in the remainder of this disclosure, all percentages are by weight, unless otherwise indicated, and all ratios are also by weight; in the case of the mixed crystal product just mentioned, (Nb,Hf)C, the ratio is in the range from 4:6 to 7:3). In the absence of more important uses, the Hf production of the zirconium industry can be absorbed by the hard metal industry.
It can thus be seen that products comprising sintered hard metals where the conventional hexagonal tungsten carbide has been partly replaced by MoC, Mo(C,N) or (Mo,W)(C,N) and where the conventional TaC or (Ta,Nb)C has been partly replaced by mixed hafnium
iobium carbides, could be expected to perform satisfactorily, whilst having the distinct advantages of being lighter and less expensive. However, the substitution of TaC by ZrC in WC-TiC-TaC hard metals has not been investigated, nor is there any such mention in the literature. The substitution of TiC
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Hall Fred W.
Retelsdorf Hans-Joachim
Brookes Anne
Hunt Brooks H.
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