Potential-pH region for environment-assisted cracking of gamma titanium aluminide

Environment-assisted cracking (EAC) of gamma-TiAl has been investigated fro m electrochemical viewpoint. The material whose potential was controlled wa s tested in aqueous sulfate solutions of various pHs at room temperature by using a slow strain rate tensile testing apparatus. The TiAl forged at 137 3 K and annealed at 1073 K for 7.2 ks was used in the EAC test. It was foun d in the alkaline and the natural solution that maximum stress was independ ent of the potential in higher potential region, and decreased with decreas e in the potential in the lower potential region. In acidic solution, the m aximum stress changed with the potential as follows; the maximum stress was independent of the potential above -200 mV(SHE), decreased with decrease i n the potential between -200 and -1000 mV(SHE), and increased with decrease in the potential below -1000 mV(SHE). The experimental EAC results was dis cussed 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 sus ceptibility of TiAl, although the diagram of Al/water system shows almost n o relation to the susceptibility. Therefore, the EAC of TiAl is controlled by the stability of Ti oxide, hydride, and ion on the solution/base materia l interface, which affect the entry of hydrogen into the material. (C) 2000 Elsevier Science Ltd. All rights reserved.