Deformation and fracture behaviors of Co-based metallic glass and its composite with dendrites

Microstructures and mechanical properties of Co-based metallic glass with nominal composition of Co43Fe20Ta5.5B31.5 (at.%) cast at the different cooling rates were investigated. When cooling rate is low enough, some dendritic crystalline phases were in situ precipitated from the glass matrix, forming the Co-based metallic glass composite with dendrites. Macroscopically, the fully amorphous samples often split apart or were broken into some particles, displaying a fragmentation failure mode. The size of particles became larger with the decrease in cooling rate. But, strength reduces slightly. Besides, the composites with dendrites show a small compressive plasticity, plus local melting behaviors with vein-like structure on the fracture surfaces. Furthermore, the effects of cooling rate on microstructures, deformation and fracture behaviors were discussed systemically. It is proposed that the fragmentation mechanism can be attributed to the inherent brittle character and high stress concentrations around the free volume. And the local melting behavior is due to the more receiving elastic energy and local shearing.