High-temperature materials

(materials) A material with high-temperature capability, including the superalloys, refractory alloys, and ceramics; used in structures such as spacecraft subjected to extreme thermal environments.

A metal or alloy which serves above about 1000°F (540°C). More specifically, the materials which operate at such temperatures consist principally of some stainless steels, superalloys, refractory metals, and certain ceramic materials. The giant class of alloys called steels usually see service below 1000°F. The most demanding applications for high-temperature materials are found in aircraft jet engines, industrial gas turbines, and nuclear reactors. However, many furnaces, ductings, and electronic and lighting devices operate at such high temperatures.

In order to perform successfully and economically at high temperatures, a material must have at least two essential characteristics: it must be strong, since increasing temperature tends to reduce strength, and it must have resistance to its environment, since oxidation and corrosion attack also increase with temperature. See also Corrosion; High-temperature chemistry.

High-temperature materials, always vital, have acquired an even greater importance because of developing crises in providing society with sufficient energy. The machinery which produces electricity or some other form of power from a heat source operates according to the basic Carnot cycle law, where the efficiency of the device depends on the difference between its highest operating temperature and its lowest temperature. Thus, the greater this difference, the more efficient is the device—a result giving great impetus to create materials that operate at very high temperatures. See also Carnot cycle; Efficiency.