The development of mixed Cr1−xAlxN nitride precipitates upon nitriding iron-based Fe-Cr-Al alloys

Abstract The development of alloying element nitrides upon gaseous nitriding of Fe–1.5 wt.-% Cr–1.5 wt.-% Al (Fe–1.6 at.-% Cr–3.1 at.-% Al) alloy was investigated, employing metallographic methods, X-ray diffractometry, electron probe microanalysis, microhardnesss measurement and (conventional, high resolution and scanning) transmission electron microscopy. It could be shown that Cr and Al do not precipitate in separate nitrides. Instead, mixed Cr1−xAlxN nitride precipitates of cubic rocksalt crystal structure develop. Upon subsequent annealing at elevated temperature, the originally mixed nitride transforms into two binary nitrides, namely CrN (cubic rocksalt crystal structure) and AlN (hexagonal wurtzite crystal structure) by outward diffusion of Al from the initially mixed nitride.