Cemented carbides and nitrides

Cemented carbides and nitrides are manufactured by a powder metallurgy process using liquid phase sintering (Figure 2.1). The cobalt or nickel binder metal, in the form of fine powder, is blended with the carbide or nitride powders in ball mills or attritor mills lined with carbide sleeves. 

A wide range of cutting-tool materials is available. Properties, performance capabilities, and cost vary widely (2,7). Various steels (see Steel) cast cobalt alloys (see Cobalt and cobalt alloys) cemented, cast, and coated carbides (qv) ceramics (qv), sintered polycrystalline cubic boron nitride (cBN) (see Boron compounds) and sintered polycrystalline diamond tbin diamond coatings on cemented carbides and ceramics and single-crystal natural diamond (see Carbon) are all used as tool materials. Most tool materials used in the 1990s were developed during the twentieth century. The tool materials of the 1990s... 

Carbides and nitrides based on the transition metals of Groups 4 through 6 of the Periodic Table have a number of special physical and mechanical properties that make them attractive for use in engineering applications. This paper discusses these properties and how they are exploited in cemented carbides and carbonitrides used in metalcutting and nonmetalcutting applications. 

Transition metal carbides and nitrides are not only inherently brittle at room temperature they are also difficult to manufacture. For engineering applications, the hard carbides (and nitrides) are therefore bonded or cemented by a ductile metal binder, usually cobalt or nickel (hence the name Cemented Carbides ). Additions of binder metal in the range of 5-20 wt% increase the toughness (transverse rupture strength) of the tools without seriously reducing hardness, rigidity, or compressive strength. Metallic binders also enable carbide products to be manufactured to full density. 

Titanium nitride coatings utilized as abrasion resistant layers on cemented carbides and as decorative layers (golden yellow) on articles of jewelry... 

Decorative. Titanium nitride has a golden color and is used extensively to coat steel and cemented carbide substrates for watch cases, watch bands, eyeglass frames, etc. It provides exceUent scratch resistance as weU as the desired aesthetic appearance, and it replaces gold coatings used previously. 

Refractory compound coatings of carbides, nitrides, and oxides on cemented carbide cutting tools, mainly by the CVD process, are estimated at 300 X 10 annually worldwide. 

Next to Cr C2, TiC is the principal component for heat and oxidation-resistant cemented carbides. TiC-based boats, containing aluminum nitride, AIN, boron nitride, BN, and titanium boride, TiB2, have been found satisfactory for the evaporation of metals (see Boron compounds, refractory boron compounds Nitrides). 

Examples of products made by the SHS process include borides, carbides, chalcogenides, hydrides, intermelallic compounds, nitrides, silicides, carbonitrides, sulfides, cemented carbides (cermets), and various heterogeneous mixtures (microcomposiles). 

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