Effect of cooling rate on the crystallization behaviors of Mg65Zn30Ca5 metallic glass composites

Metallic glass composites (MGCs) have attracted considerable attention attributing to their outstanding properties. Compared with metallic glasses, MGCs show different crystallization behaviors attributed to the embedded crystalline phases. In this work, in situ preparation of Mg65Zn30Ca5 MGCs is realized by using the differential fast scanning calorimeter. With the increase in cooling rate, the fraction of the crystalline phase in MGCs decreases exponentially. They are then reheated at rates ranging from 250 to 25,000 K/s to distinguish the role of existing crystals in the crystallization kinetics and crystal growth behaviors of MGCs. The apparent activation energy (Ea) for the crystallization of MGCs increases with the reduction of the previous cooling rate (PCR), which is attributed to the enhanced structural ordering of the amorphous phase. As a further consequence, the maximum growth rate (umax) increases because more sites for atom attachment are provided at the glass/crystal interface. Moreover, a microstructure-dependent relationship between umax and its corresponding temperature (Tu,max) is acquired, which is found to be in contrast to classical crystal growth models.