Effect of deep cryogenic cycle treatment on the microstructure and mechanical properties of Zr46Cu46Al4Ti4 bulk metallic glass

Deep cryogenic cycle treatment (DCT) is a significant rejuvenation method, critically important for research to enhance the room-temperature plasticity and associated properties of bulk metallic glasses (BMGs). In this study, Zr₄₆Cu₄₆Al₄Ti₄ bulk metallic glass (BMG) underwent 5, 10, and 15 cycles of DCT to investigate its effects on the microstructure and mechanical properties. DCT essentially does not change the thermodynamic parameters of BMG, such as T_g, T_x, and ΔT_x. The relaxation enthalpy reaches a maximum value of 14.94 J/g after 10 cycles. The results show that enhanced, reaching three to four times that of the as-cast specimens. Conversely, after 15 cycles, the BMG transforms into a low-energy relaxation state, ultimately resulting in embrittlement. This phenomenon can be attributed to the sensitivity of Zr₄₆Cu₄₆Al₄Ti₄ BMG to the number of DCT cycles. The decrease in hardness and increase in free volume resulting from DCT lead to a decline in the wear resistance of the BMG. There may be a delicate balance between the effects of DCT on the room-temperature plasticity and wear resistance of Zr₄₆Cu₄₆Al₄Ti₄ BMG. The relationship between the mechanical properties and structural heterogeneity of the BMG after DCT is also discussed.