Oxidation and electrochemical corrosion performance of Ti3Al alloy with TiAl coating

Purpose - The purpose of this paper is to investigate the high-temperature oxidation behavior in air at 900-1,000 degrees 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. Design/methodology/approach - Laboratory tests are performed to determine the effect of the Ti-48Al-8Cr-2Ag (at. %) coating on the corrosion performance of Ti3Al alloy. Findings - 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 degrees 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 degrees 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. Originality/value - TiAlCrAg coatings may become a promising protective coating for Ti3Al-base intermetallics, which improve the Al2O3 scale formation and make the passivation stable.