THE MECHANISM OF NANOCRYSTALLIZATION DRIVEN BY THE FE SI RATIO IN FE73.5CU1NB3SI22.5-XBX ALLOYS/

The kinetics of nanocrystallization were studied in two amorphous Fe-C u-Nb-Si-B based alloys with different Fe/Si ratios. Differential scann ing calorimetry and transmission Mossbauer spectroscopy data were coll ected in a range of time-temperature space. Nanocrystallization is pre ceded by a relaxation of the amorphous phase that appears to involve c hanges in its short range order (SRO) parameters [T. Pradell, N. Clava guera, J. Zhu, and M. T. Clavaguera-Mora, J. Phys.: Condens. Matter 7, 4129 (1995)] which are consistent with Cu-clustering. This process is followed by formation of Fe(Si) embryos with similar to 20 at. % Si, regardless of alloy composition. Nanocrystals with DO3 structure grow, and change composition via a diffusion controlled process that is sto pped by soft impingement [D. Crespo, T. Pradell, M. T. Clavaguera-Mora , and N. Clavaguera, Phys. Rev. B 55, 3435 (1997)]. The rate of this p rocess depends on both temperature and alloy composition. Nanocrystall ization is enhanced by prior annealing at conditions which induce SRO relaxation, however, prior annealing at an intermediate temperature (w here crystal nucleation occurs) will retard nanocrystallization. (C) 1 998 American Institute of Physics.