Hydrogen-induced hardening-to-softening transition in BCC titanium: Coupled effects of concentration and temperature

The present work employs molecular dynamics simulations to investigate the atomistic interaction mechanisms between the edge dislocation and interstitial hydrogen atoms in body-centered cubic titanium and their consequent impact on mechanical properties. The results demonstrate that the interstitial hydrogen concentration induces a characteristic volcano-type trend in the critical resolved shear stress, exhibiting initial hardening followed by softening. This is mechanistically explained by the transition from the pinning effect of Cottrell atmospheres at the low to medium interstitial hydrogen concentrations to the severe lattice distortion at high hydrogen concentrations. The temperature significantly modulates this interaction: lower temperatures promote the stable strong pinning whereas higher temperatures facilitate the dynamic thermally-assisted unpinning, leading to the reduced critical resolved shear stress and a more pronounced embrittling tendency. The synergy between high hydrogen concentration and elevated temperature critically promotes the localized deformation, offering fundamental insights into the hydrogen embrittlement mechanisms of titanium alloys.