Grain growth of nanocrystalline Fe–Al alloys produced by cryomilling in liquid argon and nitrogen

Cryomilling of Fe–10 wt.%Al powders in liquid argon as well as in liquid nitrogen resulted in nanocrystalline structures which were thermally stable at least up to 1223 K, or 67% of the melting temperature of Fe. In contrast, cryomilling of elemental Fe resulted in a nanocrystalline structure which grew to a sub-micron scale following annealing at 1223 K. The enhanced thermal stability of the cryomilled Fe–10 wt.%Al powders in liquid argon was attributed to the formation of γ-Al2O3 due to the moisture condensation. The thermal stability of the Fe–10 wt.%Al powders milled in liquid nitrogen was attributed to the formation of oxynitrides, or γ-Al2O3 and AlN particles during cryomilling in liquid nitrogen. The formation of Fe3O4 particles did not result in enhanced thermal stability. The presence of Al is essential in achieving thermal stability of nanocrystalline structures in cryomilled Fe powders.