The structural evolution and mechanical properties of a Zr-based bulk metallic glass during superplastic gas pressure forming

The structural evolution and mechanical properties of a Zr-based bulk metallic glass during superplastic gas pressure forming were investigated by differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and nanoindentation measurements at the optimum temperature of 676 K under different stress states. It was found that the crystallized volume fraction of the deformed specimens with die aspect ratios of 1:1 and 3:2 are estimated to be 15% and 25%, respectively. The high resolution TEM results show that more particles at the nanometer level exist in the deformed specimen with the aspect ratio of 3:2. The nanoindentation tests further illustrate that the Young’s modulus and hardness of the deformed specimens have increased, and the deformed sample with the aspect of 1:1 shows slightly smaller modulus and hardness. The nano-scale crystalline structure induced by gas pressure forming process is considered to be the main reason for the change of the mechanical properties, and in addition to thermal and strain energy. In addition, the structural evolution is also affected by the stress state in the process of gas pressure forming.

► A Zr-based bulk metallic glass has been bulged by the thermoplastic forming. ► The elastic modulus and hardness of the deformed specimens have been increased. ► The crystallization behaviors are very different for the two forming aspect ratios. ► The structural evolution is affected by the bulging stress state.