Effects of hydrogen as a solid solution element on the deformation behavior of a near-alpha titanium alloy

Abstract The effects of hydrogen on the room-temperature mechanical properties and the deformation behavior of near-alpha alloy Ti-6Al-3Nb-2Zr-1Mo were systematically investigated. It was found that hydrogen addition increased the strength and plasticity of titanium alloy, while the impact toughness firstly increased for the sample with 65 wppm hydrogen and then decreased at higher hydrogen content. The strength was increased due to the pinning effect and the solid-solution strengthening effect of hydrogen, while the plasticity was improved by the increase of dislocation mobility and the breakage of beta laths. The increase of impact toughness at 65wppm hydrogen resulted from the enhancement of dislocation motion and multiplication, but further increasing hydrogen addition would reduce impact toughness by decreasing the cohesion strength at interfaces and grain boundaries and the breakage of beta laths. In addition, deformation behaviors of titanium alloys with different hydrogen content were discussed. Hydrogen inhibited twinning and enhanced dislocation slip to some extent. Cross-slip was hindered and planar slip was favored due to the decrease of stacking fault energy after hydrogenation. Further, basal slip and pyramidal slip were activated while prismatic slip was suppressed by hydrogen addition.