Influence of an oxidation protective coating upon hot corrosion and mechanical behaviour of Ti–48Al–2Cr–2Nb alloy

48-2-2 specimens were coated with Au using electrochemically process and vacuum heat treatment. Au diffused and the coating was composed of TiAlAu2 and TiAlAu layers from the surface to the bulk alloy. A transition zone between the coating and the sound alloy composed of Au-enriched TiAl is also formed. The oxidation and NaCl salt corrosion behaviours of the coated specimen were investigated through cyclic tests and the effects of coating on mechanical properties of TiAl were assessed by means of creep properties. Au coating was effective in improving the oxidation and NaCl salt corrosion resistances of the coated specimens at 800 °C and 600 °C respectively. This good resistance is attributable to the formation of an Al2O3 scale on the surface of the coated specimen. During oxidation, or NaCl salt corrosion, the upper TiAlAu2 layer of the coating transformed in an Al2O3 layer on a TiAu2 layer. The slightly lower creep properties exhibited by the coated specimens are presumably linked to Cr-enriched phases that segregate at grains boundaries during the vacuum heat treatment. The degradation of creep properties after coating and corrosion is believed to be brought about either by the formation of the brittle TiAu2 phase or by corrosion or oxygen diffusion through the upper scale.