Effect of Al2O3 and enamel coatings on 900°C oxidation and hot corrosion behaviors of gamma-TiAl

The effect of reactively sputtered Al2O3 and enamel coatings on oxidation and hot corrosion behaviors of TiAl was investigated at 900°C. Isothermal oxidation testing indicated that both coatings were very effective in reducing the oxidation rate of gamma-TiAl. Cyclic oxidation testing indicated that reactive-sputtered Al2O3 coating had little effect in improving the cyclic oxidation resistance of TiAl due to the spallation of Al2O3 coating. However enamel coating exhibited an excellent positive effect on cyclic oxidation of TiAl. Enamel coating was very adherent to substrate and neither cracks nor spallation appeared in the coatings during cyclic oxidation. Furthermore, the hot corrosion behavior of TiAl with enamel coating was evaluated in (Na,K)2SO4 melts at 900°C. The results showed that enamel coating was very stable in (Na,K)2SO4 melts and was very effective in protecting TiAl from hot corrosion attack.