The cell structure of these phases have close-packed atoms in layers separated by relatively large interatomic distances. Sigma appears to be the most deleterious while strength retention has been observed in some alloys containing mu and Laves. Westinghouse Another listing of manufacturers is available from Gas-Turbines . Among the most demanding applications for a structural material are those in the hot sections of turbine engines. The widespread use of superalloys in turbine engines coupled with the fact that the thermodynamic efficiency of turbine engines is increased with increasing turbine inlet temperatures has, in part, provided the motivation for increasing the maximum-use temperature of superalloys.
Surface attack includes oxidation, hot corrosion, and thermal fatigue.
In the most demanding applications, such as turbine blade and vanes, superalloys are often coated to improve environmental resistance. Each casting technique advancement has resulted in higher use temperatures. In DS processing, columnar grains are formed parallel to the growth axis. This morphology is accomplished by pouring liquid metal into a mold that contains a water-cooled bottom plate. Solidification first occurs at the bottom plate, after which the mold is slowly withdrawn from the furnace, allowing the metal inside to directionally solidify from bottom to top.