Effect of cryogenic treatment on microstructure and mechanical behaviors of the Cu-based bulk metallic glass matrix composite

Effect of cryogenic treatment (CT) on microstructure and mechanical properties of the Cu-based bulk metallic glasses matrix composite (Cu46Zr46Al8) was investigated. CT brought about the refinement of the primary CuZr phase, the formation of the martensite phase accompanying with the morphology modification of the CuZr precipitates, contributing to the improvement in the microhardness and the compression fracture strength. The size of the CuZr crystalline phase was reduced from about 3 μm to 2 μm and the morphology of the CuZr precipitate was transformed from the rotundity to the short rod-shape. The compression fracture strength and the microhardness of the as-cast Cu46Zr46Al8 composite were 1340 MPa and 512 Hv respectively, while they were 1759 Mpa and 574 Hv respectively after CT. Furthermore, CT accelerated the fracture morphology transformation from the ductile to the brittle. The possible mechanisms involved in microstructural modification and strength as well as microhardness improvement were discussed.