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

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 Al2Au deposited by physical vapour deposition. The coated alloy was subjected to a H2/H2S/H2O yielding pS2 – 10−1 Pa and pO2 – 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, Al2O3, TiO2 and Cr2S3 developed. For the Al2Au coated Ti45Al8Nb samples an Al2O3 scale containing TiO2 nodules was observed at the surface.