Cermet and method of producing it

Details Cermet and method of producing it Cermet and method of producing it

1995-09-01

1997-09-23

Mai, Ngoclan

Specialized metallurgical processes, compositions for use therei

Compositions

Consolidated metal powder compositions

75241, 75242, 75238, 419 15, 419 16, 419 18, 419 33, 419 38, C22C 2902, B22F 312

Patent

active

056707266

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to a cermet with a hard material phase of 95 to 75% by mass, the balance being binders of cobalt and nickel. The invention relates further to method of producing such a cermet by grinding a carbide, nitride and/or carbonitride of titanium and tungsten and optionally further elements of the Groups IVa to VIa of the classification of elements, as well as a binder metal such as a cobalt and/or nickel containing mixture which is subsequently pressed and sintered.


BACKGROUND OF THE INVENTION

The JP-A-60002646 describes an alloy with a ternary hard material phase of WC, (Ti,W,Ta/Nb)C and (Ti,W,Ta/Nb)CN, whereby the alloy contains 5 to 15% by weight Co, 5 to 5% by weight (Ti,W)C, 50% by weight (Ti,W)CN, 1 to 15% by weight TaC, NbC and/or (Ta,Nb)C, the balance WC and impurities.
Cermets consisting of 25 to 50% by weight titanium nitride, niobium carbide and/or zirconium carbide, 10 to 25% by weight tungsten carbide and 7.5 to 25% by weight binders of cobalt and/or nickel, as well as optionally 0.01 to 1% by weight aluminum added to the binder and also a process for the production of the cermet are known from DE 34 18 403 C2. In the mentioned process first a formed body is produced by preliminary compression from the powder mixture of the above composition and this formed body is sintered at over 1400.degree. C. in a nitrogen atmosphere, at a pressure between 0.13 and 133 mbar.
In order to improve the toughness, U.S. Pat. No. 4,778,521 proposes a cermet composition consisting of 20 to 92% by weight titanium carbonitride, 5 to 50% by weight tungsten carbide and 3 to 30% by weight of a binder and has a triphase particle size microstructure comprising a core phase which is rich in titanium carbonitride, an intermediate phase rich in tungsten carbide surrounding the so-called core phase and an outer phase of titanium/tungsten carbonitride surrounding the previously mentioned intermediate phase. In order to produce this cermet, titanium carbide powder, tungsten carbide and nickel are mixed and further treated as shown above.
For improving the mechanical characteristics, and especially for improving the resistance against plastic deformation, the EP 0 270 509 B.sub.1 proposes to heat a mixtures of powders of TiC and (Ta, Nb) C and/or TaC after they have been mixed, and to comminute into a powder the solid solution resulting after cooling. This powder should then be mixed with carbides and nitrides or carbonitrides of metals of the Groups IVa to VIa of the classification of elements, as well as with a binder, pressed and sintered. The thereby produced body has a carbonitride component as a biphase mixture with a phase poor in nitrogen but rich in titanium and tantalum and a second phase which is rich in metal components of Group VI and in nitrogen. The first phase forms the core and is surrounded by the second phase as a marginal zone, which at the same time forms the main border surface with the binder metal alloy.
Especially for chip-removal machining operations with high cutting speeds it is proposed to prepare at first a carbonitride mixture of the composition (Ti, Ta, W)(C, N) and to mix with a binder the carbonitride powder mixture obtained this way, to grind it and to compress it into a green compact and subsequently to sinter it under nitrogen.
However according to EP 0 302 635 A1 there are two phases, the first of which (the core phase) has a carbonitride which is poor in titanium and nitrogen, while the second phase surrounding the core consists of carbonitrides rich in titanium and nitrogen. This is supposed to be achieved for instance by mixing, compacting and sintering titanium nitride or titanium carbonitride with a carbonitride of tungsten or titanium and optionally with one or further elements of Groups IVa to VIa of the classification of elements.
According to EP 0 417 333 A1 for the production of a cermet alloy in the beginning a first powder for the formation of a core structure of carbides and carbonitrides containing titanium and a second powder for the

REFERENCES:
patent: 4957548 (1990-09-01), Shima et al.
patent: 4985070 (1991-01-01), Kitamura et al.
patent: 5421851 (1995-06-01), Oskarsson et al.
"Cermets Der Neuen Generation" by Ettmayer et al. published in Metallwissenschaft + Technik, Year 43, vol. 8, Aug. 1989.

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