Abstract: Developing bulk metallic glass composites (BMGCs) with high toughness is vital for their practical application. However, the influence of different microstructures on the impact toughness of BMGCs is still unclear. The effects of Al addition and cryogenic cyclic treatment (CCT) on the Charpy impact toughness, a_K, at 298 and 77 K of a series of phase-transformable BMGCs are investigated in this work. It is found that deformation-induced martensitic transformation (DIMT) of the β-Ti dendrites is the dominant toughening mechanism in the phase-transformable BMGCs at 298 K, but at 77 K, the toughness of BMGCs is primarily determined by the intrinsic toughness of the glass matrix. The addition of Al can moderately tune the β-Ti phase stability, which then affects the amount of DIMT and impact toughness of the BMGCs at 298 K. However, at 77 K, Al addition causes a monotonic decrease in the toughness of the BMGCs due to the embrittlement of the glass matrix. It is found that CCT can effectively rejuvenate the phase-transformable BMGCs, which results in an enhanced impact toughness at 298 K. However, the toughness at 77 K monotonously decreases with increasing the number of CCT cycles, suggesting that the rejuvenation of the glass matrix affects the toughness at both 298 and 77 K of BMGCs, but in dramatically different ways. These findings reveal the influence of microstructures and CCT on the impact toughness of BMGCs and provide insights that could be useful for designing tougher BMGs and BMGCs.

Key words: Bulk metallic glass composites, Charpy impact toughness, Deformation-induced martensitic, transformation, Metastability, Thermal cycling rejuvenation