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Among the nonmetallic materials, carbides, ceramics, and cermets are finding greater usage as bearing materials. Under ordinary conditions of sliding or rolling contact, these materials have certain characteristics which are not found in bearing alloys or plastics. Low-surface energy, a property common to nonmetallics, together with extreme hardness, results in virtual freedom from self welding and galling among these materials. Friction can be high, however, in dry sliding conditions. Wear occurs by microfragmentation of carbide and oxide crystals in these materials. Fragmentation can result from cleavage of crystallites, intergranular cracking, and fatigue-type cracking. Contact state of stress and impact are significant factors in wear of ceramics and carbides. These materials are used where low-wear rates are desired under meager lubrication, at high temperatures, high speeds, and in severe environments such as liquid metal, corrosive propellants, oxidizers, abrasive slurrys, space environment, and high-temperature gases. Behavior in these environments is governed by thermal properties and surface chemical reactions characteristic of this class of materials. Lubrication can be accomplished by providing constituents which will form boundary films by chemical reaction with a given environment. Certain fluids will cause accelerated deterioration of ceramic and carbide surfaces under rolling or sliding contact conditions.
friction, wear, wear tests, surface fatigue, thermal shock, rolling contact loads, Rebinder effect, frictional anisotropy, evaluation, tests
Glaeser, W. A.
Associate fellow, Battelle Memorial Institute, Columbus, Ohio