First-principles study of four mechanical twins and their deformation along the -axis in pure α-titanium and in titanium in presence of oxygen and hydrogen

Abstract Interstitial solutes such as oxygen and hydrogen have an important and complex role on the mechanical properties of titanium. With ab initio calculations, we get the atomic structures and energies of the three most common twin boundaries (TBs) observed in α-Ti (hexagonal close packed), viz. { 10 1 ¯ 2 } , { 11 2 ¯ 1 } , and { 11 2 ¯ 2 } , together with the { 10 1 ¯ 1 } TB. The segregation energies of O and H to the four TBs are evaluated and their behaviour under deformation along the c-axis is investigated, in pure Ti and in presence of segregated O or H. All TBs decrease the theoretical ultimate tensile stress of α-Ti. Remarkably, the { 10 1 ¯ 2 } and { 11 2 ¯ 2 } TBs are unstable for a c-axis deformation as small as about 2%. O and H segregate to all four TBs except for O to the { 11 2 ¯ 2 } TB case. As such, they slightly enhance the { 10 1 ¯ 2 } and { 11 2 ¯ 2 } TB limited stability under c-axis deformation. They decrease the { 10 1 ¯ 1 } TB stability under high deformation and so does O for the { 11 2 ¯ 1 } TB.