Mechanism of hydride formation in Ti-Al alloys

Titanium alloys suffer a sudden catastrophic loss in ductility when the hydrogen tolerance, or a critical hydrogen concentration, is exceeded. The critical hydrogen concentration varies from alloy to alloy. The published results show that aluminum tends to inhibit the nucleation of hydride in the {dollar}alpha{dollar} Ti-Al alloys and {dollar}alphasb2{dollar} titanium aluminides. The hydride formation in {dollar}alpha{dollar} Ti-Al alloys is well documented; however, in {dollar}alphasb2{dollar} the mechanism of hydride inhibition is still controversial. The explanation of the inhibition effect of aluminum is still largely unknown. The present study is a systematic investigation of the role of aluminum in hydride nucleation in {dollar}alpha{dollar} Ti-Al alloys and {dollar}alphasb2{dollar} titanium aluminides with various concentrations of aluminum and hydrogen.; The literature results were re-analyzed and controlled experiments were carried out to explain the inhibiting effect of aluminum on hydride formation. The hydride nucleation and growth in Ti-Al alloys are explained by the synergistic effects of lattice misfit between the hydride and matrix, the rejection and segregation of aluminum, and the ordering effects. This research is expected to clear the inconsistencies and ambiguities of the previously reported results and account for hydrogen effects in Ti-Al alloys in a self-consistent manner.