Mechanical behaviours of workhardening and worksoftening bulk metallic glasses

The workhardening Cu47.5Zr47.5Al5 and the worksoftening Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 bulk metallic glasses before and after precompression deformation were characterised for thermal and mechanical behaviours. The predeformation introduces excessive free volume in both glasses. Cu47.5Zr47.5Al5 and Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 exhibit substantial workhardening and worksoftening behaviours respectively. For Cu47.5Zr47.5Al5, the precompression has a negligible effect on serrations in the plastic flow during nanoindentation, which is related to the hardening of a shear band, while for Zr52.5Cu17.9Ni14.6Al10.0Ti5.0, the precompression moderates serrations in the plastic flow during nanoindentation, which is associated with the softening of a shear band. Strengthening from mechanically induced nanocrystallites at shear bands is responsible for the workhardening of Cu47.5Zr47.5Al5, which overwhelms softening due to the introduction of excessive free volume.