Protective Effect of the Sputtered TiAlCrAg Coating on the High-Temperature Oxidation and Hot Corrosion Resistance of Ti-Al-Nb Alloy

The effect of a sputtered Ti-48Al-8Cr-2Ag (at. pct) coating on the oxidation resistance of the cast Ti-46.5Al-5Nb (at. pct) alloy was investigated in air at 1000～1100℃. Hot corrosion in molten 75 wt pct Na2SO4 25 wt pct K2SO4 was investigated at 900℃. The scale on the cast TiAlNb tends to spall in air, while the scale on coating is very adherent. The sputtered Ti-48Al-8Cr-2Ag coating remarkably improved high temperature oxidation resistance of the cast Ti-46.5Al-5Nb alloy because of the formation of an adherent Al2O3 scale. Due to the inward diffusion of Cr,Kirkendall voids were found at the coating/substrate interface. TiAlCrAg coating provided excellent hot corrosion resistance for TiAlNb alloy in molten 75 wt pct Na2SO4 25 wt pct K2SO4 at 900℃ due to the formation of a continuous Al2O3 scale.