Hydrogen absorption in titanium aluminides exposed to aqueous solutions atroom temperature

Secondary ion mass spectroscopy (SIMS) analysis of deuterium profiles was p erformed in different alpha(2), gamma or (alpha(2) + gamma) Ti-Al alloy spe cimens exposed at room temperature to deuterated aqueous solutions or humid ified air. The results support a mechanism of water dissociation on the sur face of titanium aluminides leading to the absorption of hydrogen in the al loys. The deuterium penetration depth strongly depends on the pH of the aqu eous solution, on the microstructure and on the deformation of the alloy in the considered environments. The natural surface ox:ide 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 t he (alpha(2)+ gamma) industrial alloys as evidenced by comparing the behavi or of alpha(2) and gamma single phase alloys in the same environments. The tensile properties of an as cast (alpha(2) + gamma) alloy depends both on t he orientation of the alpha(2) and gamma lamellae with respect to the tensi le axis and on the nature of the environment. Straining in aqueous solution s at room temperature induces a ductility loss of the alloy and promotes cr ack initiation on the surface. (C) 1999 Elsevier Science S.A. All rights re served.