Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1981-09-17
1984-05-29
Hunt, Brooks H.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
419 16, 419 15, 75236, 75242, B22F 312, C22C 1400, C22C 104
Patent
active
044512929
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates to sintered hardmetals, which are mixed carbides of metals selected from Groups IVb to VIb of the Periodic Table of the Elements and possibly other metals, in conjunction with binder metals or alloys of the iron group. The hardmetals of the invention concern, in particular, tungsten carbide from Group VIb and the carbides of zirconium and titanium from Group IVb, optionally together with carbides of metals of Group Vb. The extreme hardness and wear-resistance of hardmetals generally 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.
Hardmetals for the machining of materials producing short chips have consisted of tungsten carbide, WC, with cobalt as the customary iron group metal or alloy as a binder, for over five decades. For the machining of materials producing long chips, beneficial additions of titanium carbide, TiC, and tantalum carbide, TaC, have been used over the past three to four decades, leading to development and use of the now classic WC-TiC-Co and WC-TiC-TaC-Co hard metals. As substitutes for TaC, niobium carbide, NbC, hafnium carbide, HfC, and NbC/HfC mixed crystals have achieved a certain significance, whilst WC appears to be at least partly replaceable by isomorphous phases, such as MoC, Mo(C,N) and (Mo,W) (C,N), i.e. molybdenum carbide and carbonitride and mixed molybdenum/tungsten carbonitrides. Partial replacement of TiC and TaC by VC and CrC has, up to now, been accompanied by very little success.
A review of hardmetal literature has shown that, as well as the immiscible system VC-ZrC and VC-HfC, fully miscible systems having miscibility gaps are also known, for example TiC-ZrC, TiC-HfC, VC-NbC and VC-TaC. These mixed crystal systems undergo spinodal decomposition, but this property of these mixed crystals has not yet been used in hardmetal technology. Our prior discovery of the advantageous properties of mixed crystals of zirconium and hafnium carbides, described and claimed in our U.S. application Ser. No. 285,189 filed July 20, 198l has enabled spinodally-decomposing systems of these carbides to be applied in hardmetal technology; our aforesaid specification discloses sintered hardmetals and processes for making them, which contain zirconium and hafnium carbides in mixed crystal form together with one or more carbides of metals of Groups IV to VI and a binder comprising one or more metals or alloys of the iron group.
It has now been suprisingly found that additions of spinodally-decomposing complex mixed crystals based on ZrC and TiC and, optionally, one or more Group Vb metal carbides to hard metals based on tungsten carbide produce very abrasion-resistant and finegrained hardmetal materials, which are eminently suitable for making cutting tools. These hardmetals and tools made from them are superior to classical WC-TiC-TaC-Co alloys both in respect of flank wear and crater wear.
Hardmetals containing ZrC have long been studied, especially with respect to the substitution of TiC by ZrC in WC-TiC-Co alloys. The ZrC is introduced as a ZrC-WC mixed crystal. Results are not encouraging, as an amount of ZrC twice that of the TiC has to be added to achieve a hardmetal of similar performance. Investigation into the partial replacement of TiC by ZrC has been considered, but has not been carried out up to now.
According to a first aspect of this invention, a sintered hardmetal comprise tungsten carbide, spinodally-decomposing mixed crystal containing zirconium and titanium carbides and a binder comprising one or more metals or alloys of the iron group.
According to an especially preferred feature of the invention, the spinodally-decomposing mixed crystal also includes one or more carbides of metals of Group Vb, especially one or more of the carbides of niobium, tantalum and vanadium.
According to a second aspect of this invention, a sintered hardmetal is manufactured by heating a first mixture comprising zirconium and titanium carbides and optionally o
REFERENCES:
patent: Re22166 (1942-08-01), Schwarzkopf
patent: 3779745 (1973-12-01), Rudy
patent: 3971656 (1976-07-01), Rudy
patent: 4049876 (1977-09-01), Yamamoto
Hall Fred W.
Retelsdorf Hans-Joachim
Brookes Anne
Hunt Brooks H.
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