Environment-assisted cracking of gamma titanium aluminide in aqueous sulfate solutions

Environment-assisted cracking (EAC) of γ-TiAl has been investigated from electrochemical viewpoint. The TiAl was forged at 1373 K and annealed at 1073 K for 7.2 ks. The specimen whose potential was controlled was tested in aqueous sulfate solutions of various pHs at room temperature by using a slow strain rate tensile testing apparatus. The experimental EAC results evaluated by the maximum stress was discussed on the basis of the potential-pH diagram of Al and Ti/water system. It was revealed that the diagram of Ti/water system can predict the EAC susceptibility of TiAl, although the diagram of Al/water system shows almost no relation to the susceptibility. The results suggest that the EAC of TiAl is controlled by the stability of Ti oxide, hydride, and ion on the solution/substrate interface, which affect the entry of hydrogen into the material.