Ceramics

Ceramics in general have very high melting point temperature and good resistance to plastic deformation. Their densities are considerably lower than those of metals. Because of these reasons ceramic material become good candidate for high temperature applications particularly where inertia loadings are also involved. But at the same time ceramics have two greater disadvantages, viz., low ductility and thermal conductivity. Until recently these materials were only used for furnace linings where high temperature oxidation rather than creep was major consideration. Recently they are being put to use where oxidation and creep resistance and required simultaneously such as blades of gas turbines.

Ceramics powders bound together by a metallic matrix is a new type of composite material known as cermet. These cermets have been able to demonstrate greater ductility than ceramics while still retaining high temperature creep resistance to ceramics to a great extent. Tungsten carbides (WC) and titanium carbides (TiC) have been often used in the matrix of the cobalt and nickel to produce high speed cutting tools. Attempts are being made to use some sintered cermets such as silicon carbides as materials for parts in gas turbines. These materials have poor oxidation resistance and are not being put to practical applications yet.