Large-sized Zr-based bulk-metallic-glass composite with enhanced tensile properties

A large-sized Zr-based BMG composite containing coarse and spherical beta-Zr precipitates was produced using the semi-solid progressive solidification (SSPS) method. Specimens with a 6-mm-diameter gauge section fabricated from 11-mm-diameter cast rods, which are at least twice larger than those reported previously, have been used for mechanical-property evaluation. Our results show that the composite exhibits both excellent work hardening and plasticity. Both the microstructure evolution as a function of isothermal temperature & holding time and its influence on the mechanical properties were investigated. The mechanical properties of the composite are found to be closely related to microstructural features, and the tensile plasticity can be enhanced significantly with increasing the size scale of beta-Zr precipitates. It's evidenced that beta-Zr precipitates yield firstly and the plastic deformation with a significant work hardening follows as the stress exceeds the maximum elastic stress. Shear bands are found to be essentially nucleated at the interface between the beta-Zr particle and the glassy matrix. With further loading, the strain softening induced by the plastic deformation of the glass matrix increases. When the capacity of the strain softening by the matrix offsets the contribution of the work-hardening by the beta-Zr precipitates, the stress will reach the maximum value and then the necking occurs. The mechanistic understanding of the deformation mechanism in the large-sized BMG composite sheds light on the design of BMG composites with enhanced mechanical properties. (C) 2012 Elsevier Ltd. All rights reserved.