Abstract
Effects of some factors on the anodic polarization curves of TiAl-base alloys were studied in 2.5kmol·m-3 sulfuric acid at 20°C. The factors were the duration of catholic treatment (TRc) at a fixed potential of -900mV vs. SCE, alloying elements such as Cr or Mn, the content of Ti or Al, and a heat treatment at 1300°C for 1h. The results were compared with those of Ti and Al. The catholic current density (Ic) for the alloys increased, as the time of TRc increased, and attained a maximum after 80min, while the Ic of Ti and Al did not increase. The polarization curves of the alloys starting from the potential of -900mV were similar to that of Ti, that is, they had a peak (Icrit) and a passive range. The values of Icrit for the alloys were higher than that for Ti and the current density of Al at the same potential. It increased linearly on a log scale with increasing the initial Ic (Ic in) at the potential starting to sweep. And, it also decreased as Ti content increased. The effects of alloying elements and heat treatment were observed only when the time of TRc was short. It is concluded that the alloys absorb more hydrogen than Ti and Al at the condition investigated in this study, consequently the number of active sites in the gamma phase increase, and this gives rise to the difference in the polarization behavior mentioned above.
