Cobalt is a hard, white metal similar to nickel in appearance, but has a slightly bluish cast.
Uses. It is mainly used as an alloying element in permanent and soft magnetic materials, high-speed tool bits and cutters, high-temperature, creep-resisting alloys, and cemented carbide tools, bits, and cutters. It is also used in making insoluble paint pigments and blue ceramic glazes. In the metallic form, it does not have many uses. However, when combined with other elements, it is used for hard facing materials. Its primarily used as the metal, in the preparation of magnetic, wear-resistant and high-strength alloys. Its compounds give a distinctive deep blue color to glass, ceramics, inks, paints and varnishes. Cobalt occurs naturally as only one stable isotope, cobalt-59.
Capabilities. Cobalt can be welded, machined (limited), and cold-drawn.
Limitations. It must be machined with cemented carbide cutters. Welding high carbon cobalt steel often causes cracking.
Properties. Pure cobalt has a tensile strength of 34,000 psi (234,430 kPa); Brinell hardness number of 125; specific gravity of 8.9; and a melting point of 2720°F (1493°C). Cobalt alloy (Stellite 21) has a tensile strength of 101,000 psi (696,395 kPa) and is heat and corrosion resistant.
The main application of cobalt as the free metal, is in the production of certain high performance alloys.
Cobalt-based superalloys consume most of the produced cobalt. The temperature stability of these alloys makes them suitable for use in turbine blades for gas turbines and jet aircraft engines, though nickel-based single crystal alloys surpass them in this regard.