Plasticizing and work hardening in phase separated Cu-Zr-Al-Nb bulk metallic glasses by deformation induced nanocrystallization

Highlights: • CuZrAlNb bulk metallic glasses have been found to be of extraordinary plasticity and work hardening effect. • There is remarkable structural heterogeneity represented by phase separation in as-cast microstructure. • Deformation induced nanocrystallization takes place in matrix and shear bands. In this work, we report a class of phase separated Cu_{94 − x}Zr_xAl_5.5Nb_0.5 (x = 41, 44, 47, 50 at.%) bulk metallic glasses (BMGs) with extraordinary plastic strain up to 43% and work hardening effect featured in the compression strength compared with the yielding strength. Through the characterization of the microstructure, compositional distribution, free volume and activation energy of crystallization, the underlying mechanism for the plasticizing and work hardening has been investigated. It is confirmed that the structural heterogeneity due to the phase separation results in the formation of high density of free volume and low activation energy for crystallization. The deformation induced nanocrystallization (DINC) takes place in the whole region, especially in shear bands (SBs). The DINC may reduce the instabilization of SBs, resulting in the slow-down of the propagation of SBs and the initiation of more primary and secondary SBs from soft to hard region. This may be considered as the underlying mechanism for the plasticizing and work hardening of these BMGs.