Temperature-dependence of impact toughness of bulk metallic glass composites containing phase transformable β-Ti crystals

A parametric study of the Charpy impact toughness of bulk metallic glass composites (BMGCs) containing crystalline β-Ti dendrites is conducted at different temperatures. The effect of mole fractions, size and phase transformability of the dendrites in the BMGCs on impact toughness, a _K, is studied. BMGCs with non-transformable dendrites exhibit a steep drop in a _K with decreasing temperatures whereas those with transformable dendrites resist embrittlement. This is attributed to the energy absorbed during deformation-induced martensitic transformation (DIMT) in the dendrites of the phase transformable BMGC. At a specific temperature, increasing the mole fraction of phase transformable β-Ti crystals up to 70% also improves a _K, although further increase in mole fraction to 100% leads to embrittlement. The non-monotonic variation of a _K is attributed to the relative differences in confinement of the dendrite by the matrix, which directly influences the occurrence of DIMT in the former. These BMGCs are also resistant to relaxation induced embrittlement as a _K is insensitive to the casting size. The implications of these results in terms of designing BMGCs with high impact toughness for applications at low temperatures are discussed.