Crystallization Behavior and Mechanical Properties of Cu-based Bulk Metallic Glass Composites

Abstract

This work highlights the relationship between the preparation, crystallization behavior, microstructures, and mechanical properties of Cu-based bulk metallic glasses (BMGs) and their composites (BMGCs). (Cu47Zr45Al8)97.5Y1.5Nb in-situ BMGCs were prepared using isothermal annealing, and the experimental results indicate tunable mechanical properties of the alloys by processing parameter manipulation. The crystallinity of (Cu47Zr45Al8)97.5Y1.5Nb BMGCs increases with extended annealing temperature and time, while their phase transition with rising temperature follows Am (amorphous state) → Am + Cu10Zr7 →Am + Cu10Zr7 + AlCu2Zr + Al2Zr. Precipitation strengthening during annealing above 720 K (447 ºC) can enhance the alloy microhardness remarkably and achieve an optimum of 712 HV by annealing at 800 K (527 ºC) for 60 min. TEM results show that Cu10Zr7 with sizes of 12~15 nm precipitates out upon crystallization and thereby accounts for the superior compressive property. The alloy exhibits a fracture strength up to 2080 MPa after annealing at 680 K (407 ºC) for 30 min. Morphological observation of the fracture surface reveals a transition of fracture characteristics from the typical amorphous ductile manner to a brittle manner with further annealing. The investigation provides novel thoughts of BMGs processing for further performance improvement.

Keywords

• Cu-based BMGCs
• isothermal annealing
• crystallization behavior
• mechanical properties