Insights into multiple deformation mechanisms induced ultrahigh impact toughness of high-purity titanium

High-purity titanium exhibited ultrahigh impact toughness about 312.5 J/cm2 in this study. To uncover the underlying deformation mechanisms for the ultrahigh impact toughness, postmortem analysis of the deformation microstructure was performed using the electron back-scatter diffraction (EBSD) and transmission electron microscope (TEM) techniques. The results indicate that multiple deformation behaviors occurred in high-purity titanium. Dense dislocation activities were activated in the regions near and away from the crack tip. The average GND densities of the deformation microstructure (1.71 x 1015/m2 and 1.21x1015/m2, respectively) were much larger than that (0.06x1015/m2) of the initial specimen. Moreover, plentiful deformation twinning and detwinning behaviors were observed in the deformation microstructure which significantly contributed to plastic deformation and high impact toughness. Moreover, deformation induced alpha-Ti -> FCC Ti transformation was also activated which played as an additional deformation mode in the high-purity titanium. Multiple deformation behaviors including dislocation activities, deformation twinning/detwinning behaviors and deformation induced alpha-Ti -> FCC Ti transformation, were responsible for the ultrahigh impact toughness of high-purity titanium.