Isothermal oxidation behaviour of TiAl alloys prepared by spark plasma sintering with the addition of Gd under water vapour at 900 °C

In this paper, dense TiAl-xGd alloys with multiple compositions were prepared by spark plasma sintering (SPS) technique, and isothermal oxidation tests were carried out at 900 °C under a water vapour atmosphere to investigate the effect of Gd addition on the oxidation behaviour of Ti–48Al–2Cr–2Nb alloys. The results showed that Gd addition changed the oxidation kinetics as well as the crystal morphology and structure of oxide layer of TiAl-based alloys. Compared to the non-Gd-doped alloy, Gd-doped TiAl-based alloy exhibited higher oxidation resistance and the oxide layer did not flake off after 100 h of oxidation. The TiAl-0.15Gd alloy has the best oxidation resistance, the lowest mass gain and the thinnest oxide layer. The addition of Gd stabilises the Z-phase in the depletion layer and thus promotes the formation of protective Al2O3 scales. The continuous dense protective Al2O3 layer generated can effectively block the outward diffusion of Ti ions and the inward diffusion of O ions. Therefore, the addition of Gd can effectively improve the high temperature oxidation resistance of TiAl-based alloys. And the influence of water vapour on the oxidation behaviour of the alloy lies in the fact that H2O can interact with TiO2 and the presence of hydrogen defects leads to a stronger anisotropy of TiO2, thus exhibiting a directional growth of TiO2.