Cermet and process for producing it

Stock material or miscellaneous articles – Composite – Of inorganic material

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Details

428698, 428699, 428336, 428701, 419 25, 419 26, 419 33, 419 54, 419 57, 75238, 75242, 75244, B32B 900

Patent

active

058560327

DESCRIPTION:

BRIEF SUMMARY
This application is a National Phase application of PCT/DE95/00434 filed 29 Mar. 1995 and based, in turn, on German applications P4415454.2 of 3 May 1994 and P4423451.1 of 5 Jul. 1994 under the International Convention.


Field of the Invention

The invention relates to a cermet with a content of hard materials of 95 to 75% by mass and the balance of 5 to 25% by mass of binder to a process for the production of such a cermet by blending, grinding, granulation and compression of an initial blend of corresponding components and its subsequent sintering.


BACKGROUND OF THE INVENTION

IN EP 0 344 421 A1 a cermet is proposed which has either an average grain size of the hard material phase in the surface layer with respect to a core with a penetration depth of 0.05 mm, which is between 0.8 to 1.2 times the average grain size of the hard material phase in the cermet core, or at the same penetration depth relates to a binder phase which corresponds to 0.7 to 1.2 times the average binder content of the cermet core, or wherein the hardness in the mentioned penetration depth ranges between 0.95 and 1.1 times the average hardness of the cermet core. In order to produce this cermet, the starting mixture is sintered after grinding, blending and precompression, whereby in a first stage the sintering takes place at 1300 degree C or below under vacuum or in an inert gas atmosphere, while in a second stage the sintering takes place above 1300.degree. C. at a nitrogen pressure of 0.1 to 20 torr and whereby the nitrogen pressure is supposed to increase with the increasing temperature. The cooling also takes place in the presence of nitrogen.
The EP 0 368 336 B1 describes a cermet substrate with a hard surface layer, wherein the region with the maximal hardness lies at a depths between 5 .mu.m and 50 .mu.m from the substrate surface, and the substrate surface has a hardness of 20 to 90% in relation to the maximal hardness. In order to produce this cermet, the precompressed mixture is subjected to an initial temperature increase up to 1100.degree. C. in vacuum, to a subsequent temperature increase from 1100.degree. C. to a temperature range between 1400.degree. C. and 1500.degree. C. in a nitrogen atmosphere and to a final sintering in vacuum.
The EP 0 374 358 B1 describes a process for the production of a cermet with 7 to 20% by weight binder phase and a hard phase of titanium carbide, titanium nitride and/or titanium carbonitride with 35 to 59% by weight Ti, 9 to 29% by weight W, 0.4 to 3.5% by weight Mo, 4 to 24% by weight of at least one metal among Ta, Nb, V and zirconium, 5.5. to 9,5% by weight N.sub.2 and 4.5 to 12% by weight C. The formulated mass, blended, dried and precompressed, is sintered in such a manner that the temperature is increased to 1350.degree. C. in a vacuum, whereby the nitrogen atmosphere is set to 1 torr at 1350.degree. C., the partial nitrogen pressure being gradually increased together with a temperature increase from 1350.degree. C. up to the sintering temperature, whereby the nitrogen atmosphere is set at 5 torr when the sintering temperature is reached.
The EP 0 492 059 A3 describes a cermet body, whose hardness at a penetration depth of no less than 1 mm is higher than in the cermet interior, whereby the binder proportion can be reduced in a layer thickness of 0.5 to 3 .mu.m when compared to the core substrate. The cermet should have a hard material coating with a thickness of 0.5 to 20 .mu.m of carbides, nitrides, oxides and borides of titanium and Al.sub.2 O.sub.3. In order to produce this body, a green compact is preheated at first under vacuum to a temperature between 1100.degree. C. and 1400.degree. C., subsequently nitrogen gas is introduced up to a pressure wherein the partial nitrogen pressure ranges between 5 and 10 torr, so that the nitrogen is removed from the substrate surface. The sintering and the final cooling are performed in a nonoxidizing atmosphere, such as a vacuum or in an atmosphere of inert gas. Finally the body is coated by CVD or PVD.
For the production of a cermet wit

REFERENCES:
patent: 5308376 (1994-05-01), Oskarsson
patent: 5336292 (1994-08-01), Weinl et al.

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