Various rejuvenation behavior of Cu-Zr-Al-(Sn) metallic glass via deep cryogenic cycling treatment

Deep cryogenic cycling treatment (DCT) has been used to rejuvenate Cu-Zr-Al-(Sn) bulk metallic glasses (BMGs). The thermally treated samples exhibit rejuvenated behaviors characterized by improved enthalpy of relaxation and plasticity. Notably, the degree of rejuvenation varies significantly in Sn-doped samples compared to the Sn-free counterparts. Molecular dynamics simulations reveal that Sn doping leads to a decrease in the peak height of Cu-Zr atom pairs and a significant increase in Zr-Zr atom pairs. The negative mixing heat between Sn and Zr results in the degradation of short-range ordered structures between Cu-Zr, generating the clusters with more Zr atoms and a subsequently more closely packed structure. Such structural modification is associated with the less obvious rejuvenation in Sn-doped samples. Furthermore, the addition of Sn reduces the fraction of polyhedral structures with higher five-fold symmetry, particularly <0, 0, 12, 0>, thereby negatively impacting the rejuvenation behavior during DCT. The changes in microstructure during rejuvenation also influences the shear localization under external shear deformation. The reduction in the proportion of polyhedra with relatively higher five-fold symmetry, such as <0, 0, 12, 0>, leads to a more pronounced activation in local regions. These activated local shear units contribute to the delocalization of shear flow and the initiation of additional shear bands. The present study sheds light on the intricate interplay between Sn doping, microstructural changes, and the resulting mechanical properties in metallic glasses subjected to deep cryogenic cycling.