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

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)_97.5Y_1.5Nb 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)_97.5Y_1.5Nb 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