A study of cooling process in bulk metallic glasses fabrication

To study the temperature distribution and evolution during bulk metallic glasses fabrication, finite element method was taken to simulate the cooling process in glassy alloys fabricated by water quenching and copper mold casting. The temperature distribution and evolution in different-sized samples in the two methods were successfully reproduced. The result showed that the temperature distribution in the alloy was strongly affected by fabricating method. Two relations were then proposed to estimate the cooling rate in different-sized samples prepared by these two methods. By comparing the reported data of critical size and critical cooling rate, we showed that the reported critical size and critical cooling rate of metallic glasses didn’t follow a heat transfer relation. Those critical-sized glassy alloys actually experienced cooling rates much larger than the critical cooling rates estimated by the classical nucleation theory or experiments on milligram-scaled samples. It results from the increasing degree of heterogeneity with sample size, and therefore a larger sample requires a faster cooling rate to avoid crystallization. This work clearly shows the temperature field evolution in bulk metallic glasses fabrication and reveals that the critical cooling rate of metallic glasses might be size-dependent