Influence of laser surface melting treatment on the surface composition and mechanical properties of a Zr₆₅Al_7.5Ni₁₀Cu_12.5Ag₅ bulk metallic glass

A Zr₆₅Al_7.5Ni₁₀Cu_12.5Ag₅ bulk metallic glass (BMG) containing immiscible elements was prepared in the diameter range up to 5 mm by injection copper mold casting. The effects of the laser surface melting (LSM) treatment on the surface composition and mechanical properties of the Zr-based BMG were examined. It is found that the plasticity of the LSM-treated specimens is improved significantly by ~50% as compared with that of the as-cast ones, accompanied by the enrichment of Zr content through the reductions in Cu and Ag elements by LSM-induced evaporation. It is further noticed that the enhancement of plastic deformability is much distinct for the specimen with a larger size. The effects of LSM treatment is studied by considering the LSM-treated specimen as a kind of composite with the uninfluenced zone as the substrate and the influenced zone as the second phase. The plasticity enhancement of LSM treatment is closely related to the interaction between the influenced zone and the uninfluenced zone. Furthermore, it is assumed that the effectiveness of LSM treatment in plasticity enhancement will decrease when the volume fraction of the influenced zone exceeds a critical value due to the lack of interaction between the influenced zone and the uninfluenced zone, which is consistent with the experimental results. These results are promising for extending the applications of LSM treatment for the improvement of mechanical properties of BMGs.