Stock material or miscellaneous articles – Composite – Of metal
Patent
1997-11-20
2000-09-26
Turner, Archene
Stock material or miscellaneous articles
Composite
Of metal
428469, 428697, 428698, 428699, 75241, 75242, 75255, B22F 3105, B01J 1912, C22C 2900
Patent
active
061240400
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a composite material, consisting substantially of balance being a carbon nitride phase or binder metal phase, except for a WC-CO hard metal with up to 25% by mass cobalt as binder metal or
The invention further relates to a process for the production of this composite material.
BACKGROUND OF THE INVENTION
Composite materials of the mentioned kind are mostly used as cutting plates for machining operations or as materials resistant to high temperatures. According to the state of the art materials of the above-mentioned kind are produced through the sintering of pressed bodies made of the corresponding mixtures of hard substances and metal powders, or just of metal powders. The sintering takes place in heatable ovens, which for instance are equipped with graphite heating elements, whereby the heating of the samples takes place indirectly by the radiation emitted by the heating elements, as well as by convection or heat conduction. The drawback of this process is in that the selection of the oven atmosphere is limited by the chemical properties of the heating elements. Furthermore the heating of the hard metals, cermets or steel takes place from the outside in and is substantially controlled by the heat conduction capability and the emissivity of the samples. Depending on the heat conductivity of the samples, the variation range of the heating and cooling ratios is strongly limited, and for this reason expensive steps, and apparatus are required for a satisfactory sintering of for instance ultra-fine hard metals.
In the CN 1050908 it has already been proposed to sinter a WC-CO hard metal with 6% by mass and a small addition of 0.5% by mass TaC in a hydrogen atmosphere at 1250.degree. C. for 10 to 20 minutes in a microwave field, but this process seemed to be limited to such bodies which have only a small metal content. In the case of massive metallic bodies it has been specifically stressed that these can practically not be heated by the microwave. Moreover they reflect the irradiation effect even at the surface areas, due to their high electric conductivity and to the occurring eddy currents.
OBJECT OF THE INVENTION
It is the object of the present invention to improve the bending strength and hardness of a composite material as mentioned in the introduction and to indicate a process for the production of such a composite material.
DESCRIPTION OF THE INVENTION
This object is achieved with a composite material which, according to the invention, is produced by sintering in a microwave field. It has namely been surprisingly found that with higher contents of metal binder in the prefabricated pressed body, it has become possible to increase the efficiency of microwave heating also in hard metals. Microwave-sintered cermet materials, as well as microwave-sintered steel produced through the process of powder metallurgy have so far not even been mentioned in the technical literature. In contrast to the heretofore used conventional sintering, the microwave sintering represents a direct heating in bulk of composite materials of any desired geometry, with the only rule to be observed that the size of the sinter bodies lie within the order of magnitude of the wavelength of the used microwave radiation. In contrast to the heretofore existing practice, also bigger components can be sintered without pressure, since the high variability of the heating conditions allows for an intended structural setting in the entire component. Although the composite materials with good electrical conductivity reflect a part of the microwave radiation depending on their content of metal binder phase, the particular microstructure, especially in porous hard metal and cermet greens, makes possible a high depth penetration of the microwave radiation in the precompacted pressed body at already low temperatures.
Advantageous, from the point of view of a higher density, when the composite materials are additionally subjected to a final hot isostatic pressing (HIP), preferably at a pressure
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Gerdes Thorsten
Kolaska Hans
Rodiger Klaus
Willert-Porada Monika
Dubno Herbert
Turner Archene
Widia GmbH
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