Hydrogen atom occupancy variation induced fragile to strong transition of titanium hydride

Hydrogen embrittlement is a prevalent issue that restricts the use of titanium as a structural material. To comprehend the hydrogen embrittlement mechanism, it is necessary to investigate the intrinsic mechanical properties of hydrides in titanium. In this study, a fragile to strong transition is observed in delta-TiH2 at 423 K. The in situ high temperature nuclear magnetic resonance measurements reveal that the occupancy of hydrogen atoms undergo a transition from octahedral sites to tetrahedral sites at the same temperature. Further first-principles calculations reveal that the decrease in the generalized stacking fault energy, resulting from the modification in the hydrogen atom occupancy, is the primary reason for the enhancement in the mechanical properties of delta-TiH2. This study suggests comprehending hydride fracture toughness through the lens of hydrogen atom occupancy, providing a novel research perspective on the hydrogen-induced embrittlement mechanism in titanium alloys.