Consolidation of Cu-based amorphous alloy powders by high-pressure torsion

We applied high-pressure torsion (HPT) for consolidation of gas-atomized metallic glass Cu54Zr22Ti18Ni6 powders into high-density bulk disks. The effects of the number of revolutions (N = 1-5 turns), applied pressure (2.5-10 GPa), and temperature (298-473 K) on densification and structural changes were investigated. The consolidated glassy disks showed an excellent hardness of similar to 5.2 GPa although a mechanical softening effect along with fragmentation in the center of HPT disks occurred at N > 3 by a couple of branching cracks. The HPT process at higher applied pressures improved the bulk density and inter-particulate bonding, resulting in higher hardness. Increasing the temperature of HPT processing enhanced the densification and deep drawability of the consolidated metallic glass. Although the HPT process did not change the crystallization temperature of the metallic glass powders, it increased the crystallization enthalpy, suggesting the free volume increase and inhibition of a significant nanocrystallization during the HPT process.