Introduction
Throughout the history of its development, the gas turbine has been limited in power and efficiency by the availability of materials that can withstand high stress at high temperatures. Where conditions are at their most extreme, in the first stage of the engine, nickel and cobalt-based superalloys are currently used because of their unique combination of high-temperature strength, adequate ductility and oxidation resistance. Typical of these is MAR–M200, an alloy based on nickel, strengthened by a solid solution of W and Co and by precipitates of Ni3(Ti,Al), and containing Cr to improve its resistance to attack by gases (Table 19.3).