GRAIN-GROWTH OF NANOCRYSTALLINE CRYOMILLED FE-AL POWDERS

Nanocrystalline Fe-xAl (x = 0, 2.6, or 10 wt pet) powders have been pr epared using cryogenic mechanical alloying (cryomilling). The extremel y low rate of diffusion of Al in Fe at the process temperature (-196 d egrees C) effectively limits dissolution of Al in the nanocrystalline alpha Fe grains. Thermal stability against grain growth in the cryomil led Fe-Al mixtures is found to be much greater than that of identicall y prepared pure nanocrystalline Fe. Heat treatment of the cryomilled F e-Al materials results in a highly inhomogeneous distribution of grain size and microchemistry. The observed thermal stability is evaluated in terms of Zener pinning, solute drag, and chemical ordering mechanis ms.