Hydrogen absorption in titanium aluminides exposed to aqueous solutions at room temperature

Secondary ion mass spectroscopy (SIMS) analysis of deuterium profiles was performed in different α2, γ or (α2+γ) Ti–Al alloy specimens exposed at room temperature to deuterated aqueous solutions or humidified air. The results support a mechanism of water dissociation on the surface of titanium aluminides leading to the absorption of hydrogen in the alloys. The deuterium penetration depth strongly depends on the pH of the aqueous solution, on the microstructure and on the deformation of the alloy in the considered environments. The natural surface oxide layer is shown to impede the water dissociation and to act as a barrier to hydrogen diffusion in the alloys. This phenomenon strongly depends on the microstructure of the (α2+γ) industrial alloys as evidenced by comparing the behavior of α2 and γ single phase alloys in the same environments. The tensile properties of an as cast (α2+γ) alloy depends both on the orientation of the α2 and γ lamellae with respect to the tensile axis and on the nature of the environment. Straining in aqueous solutions at room temperature induces a ductility loss of the alloy and promotes crack initiation on the surface.