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 liqu id nitrogen resulted in nanocrystalline structures which were thermall y stable at least up to 1223 K, or 67% of the melting temperature of F e. In contrast, cryomilling of elemental Fe resulted in a nanocrystall ine 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 gamma-Al2O3 due to the moisture condensation. The thermal stability of the Fe-10 wt.%Al powders milled in liquid nitrogen was attributed to the formati on of oxynitrides, or gamma-Al2O3 and AlN particles during cryomilling in liquid nitrogen. The formation of Fe3O4 particles did not result i n enhanced thermal stability. The presence of Al is essential in achie ving thermal stability of nanocrystalline structures in cryomilled Fe powders. (C) 1998 Elsevier Science S.A. All rights reserved.