Effects of Al-2lTi-23Cr coatings on oxidation and mechanical properties of TiAl alloy

Ti-48Al specimens were coated with A1-21Ti-23Cr film of approximately 10 mum thickness at 200 W, 0.8 Pa and 300 degreesC 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 TiA1 alloy was, in particular, assessed by means of focusing on the tensile properties, which also provided the key to investigate the adhesion between TiA1 substrate and A1-21Ti-23Cr coating and between A1-21Ti-23Cr coating and Al2O3 scale. The isothermal and cyclic oxidation curves showed that the A1-21Ti-23Cr coating was very effective in improving the oxidation resistance of Ti-48A1 at 1000 degreesC. This excellent oxidation resistance is attributable to the formation of a protective A1(2)O(3) 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 A1(2)O(3) scale were not found. From the tensile test, it was confirmed that the Al-21Ti-23Cr coating enabled Ti-48A1 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-48A1 when exposed at 1000 T. Thus, it could be suggested that the A1-21Ti-23Cr coating provides the key, not only to improve oxidation resistance, but also to maintain the mechanical properties of TiA1 alloy. (C) 2002 Elsevier Science B.V. All rights reserved.