Non-monotonic influence of cryogenic thermal cycling on rejuvenation and impact toughness of Ti-based bulk metallic glass composites

Cryogenic thermal cycling (CTC) can alter the energy states of bulk metallic glasses (BMGs) and their composites (BMGCs), but the fundamental mechanisms of CTC and their effects on mechanical properties are largely remain elusive. Herein, the effects of CTC on structural evolution and impact toughness, a_K, of Ti-based BMGCs containing β-Ti dendrites are investigated. It is found that either rejuvenation or relaxation alternately dominates the structural evolution of the glass matrix, causing a non-monotonic rejuvenation. At 298 K, a more rejuvenated state causes a synergistic toughening by both of the glass matrix and dendrites, and the a_K variation trend of BMGCs is the same as the non-monotonic rejuvenation. However, at 77 K, the a_K variation trend of BMGCs is just opposite as the non-monotonic rejuvenation of the glass matrix. The rejuvenation/relaxation during CTC are correlated with the impact toughness, which provides a basis for improving toughness of BMGCs by CTC.