High impact resistance of a TWIP β titanium alloy: linking the multi-scale deformation and fracture mechanisms

Abstract

Titanium alloys with twinning- and transformation-induced plasticity effects display promising mechanical properties, particularly, high impact toughness, unlike conventional titanium alloys. This work focuses on a highly strain-hardenable Ti–Cr–Sn alloy displaying both TRIP and TWIP effects upon quasi-static loading and an average impact toughness of 193 J/cm2, which represents nearly three times the measured value for commercial titanium alloys. To account for this extremely high impact toughness, fracture and deformation features were quantified at different scales using scanning electron microscopy and transmission electron microscopy, particularly a Precession-Assisted Crystal Orientation Mapping system. Examinations evidenced the major role of twins in the fracture process, even on a sub-micrometre scale. The high impact resistance and absorbed energy of this alloy are explained by the positive contribution of dynamical refinement of the β grains with sub-twinning structures, whereas severe stress concentration may eventually contribute to ductile fracture, at least locally.