Sulphidation/oxidation behaviour of TiAlCr and Al2Au coated Ti45Al8Nb alloy at 750°C

Abstract In this paper, we present the sulphidation/oxidation behaviour of a Ti45Al8Nb (at%) alloy coated with different protective surface films. Two intermetallic coatings are considered; TiAlCr and Al 2 Au deposited by physical vapour deposition. The coated alloy was subjected to a H 2 /H 2 S/H 2 O yielding pS 2 – 10 −1 Pa and pO 2 – 10 −18 Pa potentials at 750 °C for up to 1000 h. The corrosion kinetics were determined by means of discontinuous gravimetry and the as-received and exposed samples were characterised using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction analysis (XRD). The materials showed the development of a multilayered structure. In the case of the TiAlCr coated Ti45Al8Nb – base alloy, Al 2 O 3 , TiO 2 and Cr 2 S 3 developed. For the Al 2 Au coated Ti45Al8Nb samples an Al 2 O 3 scale containing TiO 2 nodules was observed at the surface.