Nanocrystallization of Al_(92)Sm_8 amorphous alloy studied in situ by real-time x-ray diffraction

摘要

We have investigated the in situ isothermal nanocrystallization kinetics of binary Al_(92)Sm_8 glassy alloy using time-resolved x-ray diffraction. From diffraction spectra parameters we have calculated the mean grain size and crystalline phase volume fraction. The results show that the average grain size does not change by more than 15 percent of its initial value in the course of the nanocrystallization process. The first nanocrystals contributing to the crystalline phase signal are characterized by a mean crystal size of 11 nm which increases up to 13 nm at the end of the primary crystallization stage. These results are in agreement with a TEM analysis. Our observations indicate the very significant difference in growth rate of small and large clusters. Further, they show that the transformation kinetics is governed by the nucleation rate. We conclude that diffusion controlled growth plays a minor role in the overall transformation kinetics. Possible origins of the observed crystallization behaviour are given.