Synthesis of ternary nitrides from intermetallic precursors: Modes of nitridation in model Cr₃Pt alloys to form Cr₃PtN antiperovskite and application to other systems

The use of intermetallic alloy precursors is explored as a new means to synthesize complex transition and refractory metal nitrides, carbides, and related phases. The conditions under which model single-phase Cr₃Pt and two-phase Cr₃Pt-dispersed Cr alloys form Cr₃PtN antiperovskite when thermally nitrided were studied. Phenomenological experiments suggest that the key variable to achieving single-phase Cr ₃PtN surface layers is the Cr₃Pt phase composition. In two-phase β-Cr-Cr₃Pt alloys, the formation of single-phase Cr₃PtN at Cr₃Pt precipitates by in-place internal nitridation was found to be a strong function of the size of the Cr ₃Pt dispersion in the microstructure. Nanoscale Cr₃Pt dispersions were readily converted to near single-phase Cr₃PtN, whereas nitridation of coarse Cr₃Pt particles resulted in a cellular or discontinuous-type reaction to form a lath mixture of Cr₃PtN and a more Cr-rich Cr₃Pt or β-Cr. The potential for using such external/internal oxidation phenomena sa as a synthesis approach to layered or composite surfaces of ternary ceramic phases (nitrides, carbides, borides, etc.) of technological interest such as the Ti₃AlC₂ phase, bimetallic nitride, and carbide catalysts (Co₃Mo₃N and Co₃Mo₃C and related phases), and magnetic rare earth nitrides (Fe₁₇Sm₂N_x or Fe₁₇Nd ₂N_x) is discussed.