Alloy design of intermetallics for protective scale formation and for use as precursors for complex ceramic phase surfaces

This paper highlights some evolving new design approaches to developing intermetallic alloys capable of protective scale formation and/or for their use as precursors for functional complex ceramic phase surface synthesis. The unique characteristics of intermetallics present challenges to achieving protective scale formation, but also offer the potential for leveraging novel phenomena not generally observed in conventional alloys. Examples will be drawn from the oxidation of aluminides (Fe3Al, Nb2Al, NbAl3, Ti3Al, TiAl), silicides (MoSi2, Mo5Si3, Mo–Si–B, Ti5Si3), and Laves phases (Cr2Nb, Cr2Ta, Nb(Cr,Al)2, Ti(Cr,Al)2). Recent work also suggests that intermetallics can be used as precursors for the synthesis of functional complex ceramic phase surfaces by gas–metal reactions (oxidation, nitridation, carburization, etc.). The potential for using such reaction phenomena to synthesize layered or composite surfaces of ternary nitrides (carbides, borides, etc.) of technological interest such as Ti3AlC2, bimetallic nitride and carbide catalysts (e.g. Co3Mo3N or Co3Mo3C), and magnetic rare earth nitrides (Fe17Sm2Nx or Fe17Nd2Nx), from intermetallic precursors is discussed.