CUTTING-TOOL MATERIALS SUBSTRATE

Another approach is to coat the cutting tool material with a carbide former, such as titanium or siUcon or their respective carbides by CVD and deposit diamond on top of it. The carbide layer may serve as an iaterface between diamond and the cemented carbide, thus promoting good bonding. Yet another method to obtain adherent diamond coatings is laser-iaduced microwave CVD. By ablating the surface of the substrate with a laser (typically, ArF excimer laser) and coating this surface with diamond by microwave CVD, it is possible to improve the adhesion between the tool and the substrate. Partial success has been achieved ia this direction by many of these techniques. 

Substrates. Suitable substrates for TiC deposition are the cemented carbides, such as tungsten carbide (WC) bonded with cobalt (Co), which are widely used as cutting-tool materials (see Ch. 16). Other substrates coated by TiC are molybdenum and graphite. 1 1 In the case of molydenum, it is essential to maintain the deposition temperature below 950"C, otherwise recrystallization of the metal and reduction in mechanical strength will occur. 

Substrate Materials. Cemented tungsten carbide (WQ is a major substrate cutting tool material. It has been successfully coated with CVD diamond with good adhesion especially with an intermediate carbide-former layer.l JI ... 

The major cutting-tool substrate materials are high-speed tool steel, cemented carbides and, more recently, ceramics and diamond. The share of these materials of the total cutting-tool market is estimated as follows (in 1996) ... 

As a conclusion of these results, the optimal cutting speed and tool material, including substrate and coating, should be selected according... 

As a conclusion of this section, let us characterise briefly the electronic structure investigations of one more group of materials whose properties are greatly dependent on surface effects. These are thin films made from refractory carbides and nitrides. These films find applications in microelectronics, optics and as coatings for cutting tools and other complicated multilayered materials. Such films can be produced by different methods, such as thermal deposition or laser evaporation, (Morchan, 1982), molecular-beam epitaxy and cathode sputtering (Herman, 1982 Cho, 1983), plasma condensation in vacuum with ionic bombardment of the substrate surface (Dorodnov and Potrosov, 1981), chemical vapour-phase deposition (Anikeev, 1977 Anikin, Anikeev and Zolotaryova, 1979), etc. 

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