In this work, a small amount of Nb has been added in a Zr₅₂Cu_42.5Al_5.5 bulk metallic glass, and a Zr₅₂Cu₄₂Al_5.5Nb_0.5 bulk metallic glass composite with dual-amorphous and nanocrystal structures has been developed for the first time. This in situ formed bulk metallic glass composite has a larger room compressive plasticity of above 13% than that of the Zr₅₂Cu_42.5Al_5.5 bulk metallic glass. The excellent plasticity of the bulk metallic glass composite is attributed to the phase-separated matrix with micro-nanocrystal and the nanocrystallization during the deforming process. This work may give a new sight into design bulk metallic glass composites and the underlying mechanism for deformation.

The effects of different strain levels applied through high-pressure torsion (HPT) deformation following annealing on the microstructural evolution, thermal stability, and mechanical properties of Al-4Mg-0.3Cu alloy were investigated. The results reveal that Cu-segregated grain boundaries (GBs) were generated in the ultrafine-grained Al-4Mg-0.3Cu alloy with high angle grain boundaries. By contrast, the phenomenon of Cu segregation was not found in micron-scale and submicron-scale grains with low-angle grain boundaries. The mechanism of Cu segregation in ultrafine-grained Al-4Mg-0.3Cu alloy was discussed. After heat treatment, Cu segregation induced the precipitation of the dense Al₂CuMg phase at GBs, which strongly inhibit grain growth and improve thermal stability. Stress–strain curves of as-cast, 5-turn, and 10-turn HPT samples showed that fracture strength significantly increased, attributed to grain size refinement, dislocation density increase, and Cu segregation at GBs. After heat treatment, 5-turn and 10-turn HPT samples demonstrate an enhanced elongation to fracture with a slight reduction of fracture strength.