Effect of hydrogen-vacancy cluster on the tensile strength of alpha-titanium twin boundaries: A first-principles investigation

This study investigated the formation of hydrogen-vacancy cluster at twin boundaries (TBs) in alpha-titanium and their impact on TB strength. Using first-principles calculations, it is found that a single vacancy (V^A) on the {10−12} TB plane can trap up to five hydrogen atoms, while the single V^A on the {10−11} TB plane can accommodate up to eight hydrogen atoms. The presence of V^A weakens TBs by reducing the number of Ti-Ti bonds near the TBs. However, in the {10−12} TB with V^AH₅, the enhancement effect of Ti-H-Ti bonds dominates over the weakening effect of electron transfer, resulting in a slight increase in tensile strength compared to {10−12} TB with V^A. On the other hand, in the {10−11} TB with V^AH₈, the weakening effect of electron transfer dominates, leading to a further reduction in tensile strength relative to {10−11} TB with V^A. Therefore, the effect of hydrogen-vacancy cluster on the strength of twin boundaries is sensitive to the type of twin boundary. These findings provide valuable insights into the role of hydrogen in the embrittlement of alpha-titanium.