Effect of preannealing on glass transition and crystallization of gas atomized Cu47Ti33Zr11Ni8Si1 metallic glass powders

Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used as the main method to investigate the effect of relaxation on the glass transition and crystallization of Cu47Ti33Zr11Ni8Si1 metallic glass powders. The preannealing treatments were performed at temperatures close to the experimentally determined glass transition temperature. It was found that the thermal stability is profoundly affected by preannealing since the crystallization temperature is strongly influenced by preannealing and decreases with increase in preannealing temperature. In contrast, the annealing treatment does not change the glass transition temperature. During heat treatment at temperatures around the calorimetric glass transition temperature, Tg, the glassy powder undergoes microstructural alterations as revealed by TEM but not discernible by XRD. Fine nanocrystals of about 4–6 nm homogeneously dispersed in an amorphous matrix are observed by TEM after annealing at 698 K for 60 min. Kissinger analysis reveals that the preannealing decreases the activation energy for nanocrystallization thereby promoting partial crystallization of the glass.