Influence of relaxation and crystallization on micro-hardness and deformation of bulk metallic glass

The development of super-plastic precise forming technology, utilizing viscous flowing property exhibited by bulk metallic glasses (BMGs) in super-cooled liquid region, will lead to wider applications of these alloys. During the process of super-plastic forming in high temperature of BMGs, relaxation is inevitable and crystallization will occur if adopting unsuitable forming process. So it is very meaningful to realize how relaxation and crystallization influence the mechanical properties of BMGs. In this paper, the samples of Zr41.2Ti13.8Cu12.5Ni10Be22.5 BMG are annealed under different conditions. The relaxation and crystallization behaviors, the micro-hardness of the annealed samples are analyzed and measured. The deformation behaviors of the annealed samples in super-cooled liquid region are investigated by small punch test (SPT). The results show that the structure relaxation caused by annealing at the temperature lower than glass translation temperature Tg makes the micro-hardness increase slowly, but the crystallization caused by annealing at the temperature higher than Tg makes the micro-hardness increase rapidly and along with the crystallization proportion arising. Structure relaxation engenders a little influence on the plasticity of BMG in super-cooled liquid region, but slightly crystallizing makes the deformation load increase rapidly. The bulk metallic glass displays different degrees of brittleness as the crystallization proportion increases. The suitable super-plastic forming time of Zr41.2Ti13.8Cu12.5Ni10Be22 BMG at 390 °C is 10 min. The deformation force of the alloy increases rapidly when the forming time exceeds 10 min and the plasticity decreases rapidly when the forming time exceeds 30 min.