Abstract
Titanium aluminide alloys containing the DO19α2 (Ti3Al) phase, such as Ti-25Al-10Nb-3V-1Mo (at.%), are known to be sensitive to hydrogen. Such alloys could provide an alternative for conventional Ti alloys in a hydrogen-rich environment, and an understanding of the hydrogen embrittlement mechanisms acting in these materials is needed. Hydrides are known to form in conventional Ti alloys. Hence, a systematic study was undertaken to investigate the possibility of hydrogen-induced second phases in the Ti-25Al-10Nb-3V-1Mo alloy. We report here that internal hydrogen results in the precipitation of an orthorhombic OH phase in the α2 grains. The morphology and the orientations of the orthorhombic variants can be successfully described using group theory and the phenomenological theory of martensitic transformations.The as-received material consisted of bars extruded in the (α2 + β) phase field at 1037°C, then oil quenched. A solutionizing treatment at 1085°C, followed by free cooling at 0.1°C/s to room temperature resulted in a microstructure containing primary α2 grains and α2 secondary laths in a B2 matrix.
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