Improving the uniform elongation of ultrafine-grained pure titanium through judicious allocation of work hardening

Abstract

Improving uniform elongation in metals typically involves enhancing the work hardening rate, as elevated work hardening can delay necking and fracture. However, our investigation into commercial pure titanium reveals a counterintuitive relationship between these properties. We find that high uniform elongation correlates with low work hardening capability, while a high work hardening rate results in reduced ductility. Two types of ultrafine-grained pure titanium, prepared by rotary swaging, subsequent rolling, and annealing, exhibit different mechanical properties. Microstructural and deformation mechanism analyses reveal that the difference arise from variations in texture. Specifically, extensive activation of <c+a> dislocations in the former sample leads to premature, intense work hardening that is quickly exhausted, while the latter sample shows a steady, uniform work hardening progression that delays necking. Our findings challenge the conventional understanding that high work hardening rates ensure high uniform elongation. Instead, we propose that optimizing ductility requires a strategic allocation of work hardening throughout the tensile deformation to delay necking. This study reveals the intrinsic relationship between work hardening and ductility, offering new strategies for designing stronger and tougher materials.