Unusual plasticization for structural relaxed CuZr-based bulk metallic glass (BMG) has been found. Even though thermal-annealing usually leads to unfavourable relaxation-induced embrittlement for most BMGs, this BMG exhibits an improved plasticity after annealing. This behaviour is attributed to an evolution of nanolevel hetereogeneity for this unstable or heterogeneous BMG. Less initiation of shear bands by structural relaxation and evolution of heterogeneity from thermal-annealing are considered to contribute cooperatively to the plasticity of relaxed glass. This study provides a new viewpoint to improve the mechanical properties of BMGs upon relaxation, in which a microstructural heterogeneity is distributed among a glassy matrix. This finding may also expand the applications of BMGs as promising structural materials because of unusual resistances to annealing-embrittlement.
