Thermal stability and selective nitridation of Cr2AlC in nitrogen at elevated temperatures

Abstract

The thermal stability and selective nitridation of Cr2AlC under a high–temperature nitrogen atmosphere were studied. Cr2AlC began to decompose beyond 1073 K in N2, and the activation energy was estimated to be 108.93 kJ·mol−1. Initially, the selective nitridation led to the generation of an AlN layer, which shielded the underlying Cr2AlC and the process was dominated by a surface reaction. The final products were AlN, Cr7C3 and Cr3C2, and the weaker Cr–Al bonds in Cr2AlC facilitated the rapid diffusion of aluminum from the interior outwards. As the reaction proceeded, micropores were observed on the grain surface, as well as a loose structure, which facilitated the diffusion of N2 and thus accelerated the reaction. Finally, the intensive reaction involving Cr2AlC and N2 could be attributed to the gas diffusion channels caused by improved temperature and continuous escape of vaporized aluminum.