Oxidation and electrochemical corrosion performance of Ti₃Al alloy with TiAl coating

The purpose of this paper is to investigate the high‐temperature oxidation behavior in air at 900‐1,000°C and electrochemical corrosion performance in 3.5 percent NaCl solution of Ti‐24Al‐17Nb‐0.5Mo (at. %) alloy with Ti‐48Al‐8Cr‐2Ag (at. %) coating.

Laboratory tests are performed to determine the effect of the Ti‐48Al‐8Cr‐2Ag (at. %) coating on the corrosion performance of Ti₃Al alloy.

It is found that the oxidation rate of sputtered Ti‐48Al‐8Cr‐2Ag nanocrystalline coating is lower than that of the Ti₃Al alloy at 900°C. The former forms a scale of merely Al₂O₃ and the latter forms a scale of TiO₂. However, the Ti‐48Al‐8Cr‐2Ag nanocrystalline coating shows a slightly higher oxidation rate than did the Ti₃Al alloy at 1,000°C, because outer TiO₂ scale forms and columnar boundaries of the coating give a larger actual oxidation area than the original alloy. The coating shows the excellent electrochemical corrosion resistance in 3.5 percent NaCl solution because it exhibits stable passive polarization behavior without any overpassivation phenomena.

TiAlCrAg coatings may become a promising protective coating for Ti₃Al‐base intermetallics, which improve the Al₂O₃ scale formation and make the passivation stable.