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.