Ordering of nanocrystalline FeAl produced by cluster condensation

For studying the ordering kinetics of nanocrystalline Fe50Al50 alloys the s pecimens were prepared by sputtering, crystallite condensation in an Ar atm osphere, and subsequent compaction (2-4 GPa) at room temperature. The latti ce structure is B2 as in coarse grained FeAl but with a significantly lower degree (less than or equal to 0.5) of order The crystallite size is about 20 nm and strains exceed 1.5 % in the {110} direction and are higher than i n nanocrystalline Fe. The ordering process takes place mainly in the temper ature range from 400 to 500 K, which is measured by the x-ray intensities o f the superlattice reflections. This may indicate a higher vacancy diffusiv ity in the disordered than in the ordered state. The crystallite size remai ns smaller than 50 nm even after annealing at 0.8 T-m (melting temperature T-m = 1488 K) as evidenced by transmission electron microscopy. Furthermore the strains decrease during annealing. First results of magnetothermal ana lysis studies will be presented. (C) 1999 Acta Metallurgica Inc.