In DE 197 52 289 C1, based upon teachings from diverse literature sources, a binder reach zone that has a reduced mixed carbide level [mixed carbide poor zone] is provided proximal to the surface and having a significant influence on the ductility of the substrate body and the adhesion thereto of a coating applied to this substrate body. The transport use of this zone of the cubic missed carbide phase is carried out via a nitrification process by the introduction of nitrogen that can be depleted in a subsequent vacuum treatment and gives rise to a preferred solubilization and diffusion transport of the mixed carbide phase in the binder metal. For the production of the boundary zone or gradient structure of such a substrate body, various methods have been proposed:
for example, a nitrification treatment can be carried out on the hard metal below the melting point of the binder phase whereby the body can then be heated under vacuum to the sintering temperature. The nitrogen that is required for the nitrification can be supplied by a nitrogen atmosphere or also in the form of nitrides or carbonitrides that are admixed with the hard material carbide and from a hard metal mixture additive. The sintering is carried out under vacuum so that a gradient zone formation can arise. The gradient zone can also be obtained by subjecting the hard metal in conjunction with the sintering to a nitrogen treatment under elevated temperature during sintering in the temperature range of about 1150° C. to a maximum of 1300° C. If an alternative thereto, the sintering of the hard metal can be carried out by a dewaxing at a temperature of up to 600° C., retaining it at this temperature, then heating it to the sintering temperature and carrying out a vacuum sintering at 0.1 to 100 Pa and subsequently sintering at under pressure. After cooling down of the hard metal shaped body to a temperature below 1280° C., the sintered body is subjected to a pressure treatment with a nitrogen atmosphere at 1 to 10 MPa and a subsequent vacuum treatment at 10 to 100 Pa.
DE 197 52 289 C1 describes the drawback that a subsequent mechanical finish machining of the substrate body to produce its final contour with at least partial machining away of the boundary zone causes the gradient zone and its positive properties to be wholly or partly lost. To overcome this drawback, it is proposed in DE 197 52 289 to subsequently treat the substrate body after finish machining in vacuum at about 600 to 1300° C. over a time period of up to 150 min. On the mechanically machined surface, this can result in renewal of the zone that is enriched with the binder metals and is free from cubic mixed carbide. The thickness of this region amounts to 5 to 35 μm.