GRAIN-SIZE STABILITY OF NANOCRYSTALLINE CRYOMILLED FE-3WT-PERCENT-AL ALLOY

Nanocrystalline Fe-3wt.%Al alloy powders are synthesized using cryogen ic mechanical alloying in liquid N. Uptake of O by the powders is sign ificantly reduced by controlling the atmosphere and pressure during mi lling. The initial 18 nm grain size of the cryomilled powder is found to experience grain growth at temperatures above 500 degrees C (0.42 T -m), as determined by X-ray diffraction. Cryomilled pure Fe, in contra st, is found to be significantly less stable. Transmission electron mi croscopy indicates that the grain growth in the Fe-3wt.%Al is abnormal , while lattice parameter measurements indicate limited dissolution of Al in the Fe matrix. (C) 1997 Acta Metallurgica Inc.