On low-temperature strength and tensile ductility of bulk metallic glass composites containing stable or shape memory β-Ti crystals

Abstract

Bulk metallic glass composites (BMGCs) with in-situ formed crystals can display tensile ductility at room temperature, overcoming brittleness of monolithic bulk metallic glasses (BMGs). However, the ductility and toughness of BMGCs severely deteriorate at low temperatures, which has been a longstanding bottleneck hindering their low-temperature applications. Here, the low-temperature tensile properties of two Ti-based BMGCs containing stable β-Ti crystals with dislocation-mediated plasticity (Fe1) or shape memory β-Ti crystals (Fe0) were investigated. With temperature decreasing from 298 to 77 K, the strength of Fe1 increases but its tensile ductility decreases. In comparison, the shape memory Fe0 BMGC exhibits a simultaneous enhancement of strength and tensile ductility as temperature decreases from 298 to 143 K. The superior low-temperature properties of Fe0 are attributed to its combined structure of a glassy matrix and shape memory crystals. As temperature decreasing, the glassy matrix possesses an increased strength which softens as shear bands form, and the shape memory crystals are more inclined to deformation-induced martensitic transformation. Therefore, the combination of characteristic properties of metallic glasses and shape memory crystals in shape memory BMGCs can successfully overcome the low-temperature brittleness. These findings are believed to facilitate the development of BMGCs with superior low-temperature properties and promote their applications at low temperatures.