APPROACHES TO OXIDATION-RESISTANT REFRACTORY-METAL ALLOYS

The focus of the research reported here was on the design of high-temp erature alloys which would form protective SiO2 and Al2O3 scales on ex posure to high-temperature, oxidizing environments. One way to promote the growth of such scales is to incorporate sufficient amounts of Si or Al in the alloy substrate; typically, additions of approximately 35 to 45 weight percent (all alloy compositions are given in weight perc ent unless explicitly stated otherwise) of Si or Al would be required to form the respective scales, in the absence of additional protective -scale-forming elements. At such levels of alloying additions, the for mation of intermetallic phases is likely, which may have undesirable f eatures such as low melting temperatures or poor mechanical properties . The research described was an attempt to address these problems from a fundamentally different point of view, for Mo- and Nb-based alloys, through the use of a dispersed reservoir phase.