One of the best that is presently being used is a complex superalloy known as Inconel. It is interesting to note that some of Tesla's turbine disks were fabricated out of a material known as German Silver. This hard alloy, once commonly used for tableware, also contains nickel along with copper and zinc in varying proportions. No doubt the super high performance heat engines of the future will be constructed of even more advanced temperature resistant, high strength materials. There are a number of promising possibilities in this regard.
Components made of niobium matrix composites require an iridium coating for oxidation protection.
A third promising contestant that has been identified is a reaction milled composite called AlN dispersoid-reinforced NiAl. This nickel-aluminum alloy based material is produced by milling NiAl powder in liquid nitrogen. A related material known as single crystal NiAl has already been formed into turbine blades and could be adopted immediately. A near term benefit to be derived from the use of this material, as with the other NiAl compounds, would be a substantial reduction in weight. Furthermore, it is expected that techniques will be developed to control high temperature deformation of these oxidation resistant materials.