Unusual hardening mediated by {10–12} twins of strongly textured titanium at cryogenic temperature

Abstract

{10–12} twinning is an important deformation mechanism for hexagonal metals; however, its characteristically low critical stress and resulting high twin activity often lead to rapid strain localization and premature failure. Therefore, this study aims to strategically delay {10–12} twinning at the initial deformation stage to prevent the strain localization, and concurrently seeks to reactivate {10–12} twinning at the large deformation stage to facilitate continuous hardening. Guided by these dual objectives, we selected rolled titanium as the model material and designed the loading direction to minimize the Schmid factor of {10–12} twinning, and then introduced cryogenic temperatures as low as 77 K to apply GPa-grade stress, thereby enabling continuous strengthening until the reactivation of {10–12} twinning. Under these specified conditions, the rolled titanium exhibited markedly enhanced mechanical properties; the ultimate strength increased from 618 MPa to 1634 MPa, while the true strain was increased by approximately 0.15 when the temperature was reduced from 298 K to 77 K. More importantly, an unusual strain hardening behavior was experimentally observed at a true strain of 0.16, at which {10–12} twins started to behave as the predominant twinning mechanism. Quantitative analysis further indicated that the large majority of the strain hardening capacity was attributed to high-density {10–12} twins. The present study therefore highlighted the pivotal role of {10–12} twins and offers a novel viewpoint for designing and achieving distinctive mechanical properties through the manipulation of deformation twinning.