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 Cr3PtN surface layers is the Cr3Pt phase composition. In two-phase 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 Cr3Pt 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 (beta)-Cr. The potential for using such external/internal oxidation phenomena 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 (Fe17Sm2Nx or Fe17Nd2Nx) is discussed.