Effect of Cold Rolling on the Evolution of Shear Bands and Nanoindentation Hardness in ZrTiCuNiBe Bulk Metallic Glass.

The effect of cold rolling on the evolution of hardness () and Young's modulus () on the rolling-width (RW), normal-rolling (NR), and normal-width (NW) planes in ZrTiCuNiBe (Vitreloy 1) bulk metallic glass (BMG) was investigated systematically using nanoindentation at peak loads in the range of 50 mN-500 mN. The hardness at specimen surface varied with cold rolling percentage (%) and the variation is similar on RW and NR planes at all the different peak loads, whereas the same is insignificant for the core region of the specimen on the NW plane. Three-dimensional (3D) optical surface profilometry studies on the NR plane suggest that the shear band spacing decreases and shear band offset height increases with the increase of cold rolling extent. Meanwhile, the number of the pop-in events during loading for all the planes reduces with the increase of cold rolling extent pointing to more homogeneous deformation upon rolling. Calorimetric studies were performed to correlate the net free volume content and hardness in the differently cold rolled specimens.