Cemented carbides are composed of one or more carbide compounds bonded in a metallic matrix. The term cermet is not used for all of these materials, even though it is technically correct. The common cemented carbides are based on tungsten carbide (WC), titanium carbide (TiC), and chromium carbide (Cr3C2). Tantalum carbide (TaC) and others are also used but less commonly. The principal metallic binders are cobalt and nickel. Carbide ceramics constitute the principal ingredient in cemented carbides, typically ranging in content from 80% to 95% of total weight.
Cemented carbide parts are produced by particulate processing techniques. Cobalt is the binder used for WC, and nickel is the common binder for TiC and Cr3C2. Even though binder constitutes only about 5% to 15%, its effect on mechanical properties is significant in the composite material. Using WC-Co as an example, as the percentage of Co is increased, hardness is decreased and transverse rupture strength (TRS) is increased. TRS correlates with toughness of the WO-Co composite.
Cutting tools are the most common application of cemented carbides based on tungsten carbide. Other applications of WC-Co cemented carbides include wire drawing dies, rock-drilling bits and other mining tools, dies for powder metallurgy, indenters for hardness testers, and other applications where hardness and wear resistance are critical requirements.
Titanium carbide cermets are used principally for high temperature applications. Nickel is the preferred binder; its oxidation resistance at high temperatures is superior to that of cobalt. Applications include gas-turbine nozzle vanes, valve seats, thermocouple protection tubes, torch tips, and hot-working spinning tools. TiC-Ni is also used as a cutting tool material in machining operations.
Compared with WC-Co cemented carbides, nickel-bonded chromium carbides are more brittle, but have excellent chemical stability and corrosion resistance. This combination, together with good wear resistance, makes it suitable for applications such as gage blocks, valve liners, spray nozzles, and bearing seal rings.