Effects of Al–21Ti–23Cr coatings on oxidation and mechanical properties of TiAl alloy

Ti–48Al specimens were coated with Al–21Ti–23Cr film of approximately 10 μm thickness at 200 W, 0.8 Pa and 300 °C using RF magnetron sputtering. The oxidation behavior of the coated specimens was investigated through isothermal and cyclic oxidation tests, and the effect of coating on the mechanical properties of TiAl alloy was, in particular, assessed by means of focusing on the tensile properties, which also provided the key to investigate the adhesion between TiAl substrate and Al–21Ti–23Cr coating and between Al–21Ti–23Cr coating and Al2O3 scale. The isothermal and cyclic oxidation curves showed that the Al–21Ti–23Cr coating was very effective in improving the oxidation resistance of Ti–48Al at 1000 °C. This excellent oxidation resistance is attributable to the formation of a protective Al2O3 scale on the surface of the Al–21Ti–23Cr film. Although extensive cracking in a transverse direction was observed on the surface of the film, the delamination of the coating from the substrate and the spallation of the Al2O3 scale were not found. From the tensile test, it was confirmed that the Al–21Ti–23Cr coating enabled Ti–48Al to maintain its tensile properties regardless of exposure to oxidizing atmosphere. In addition, the result of the microhardness test indicated that the Al–21Ti–23Cr coating was very effective in suppressing the embrittlement of the Ti–48Al when exposed at 1000 °C. Thus, it could be suggested that the Al–21Ti–23Cr coating provides the key, not only to improve oxidation resistance, but also to maintain the mechanical properties of TiAl alloy.