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-Al 2O 3 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-Al 2O 3 and AlN particles during cryomilling in liquid nitrogen. The formation of Fe 3O 4 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.