Microstructure and Oxidation Behavior of NiCoCrAlY Coating With Different Sm₂O₃ Concentration on TiAl Alloy

In order to improve the oxidation resistance of TiAl alloys, NiCoCrAlY coatings with different amounts of Sm₂O₃ were prepared by laser cladding on TiAl alloys. The microstructure and oxidation behavior of the coatings were investigated by isothermal oxidation tests at 900°C. The results indicated that the grains of the coatings were refined by Sm₂O₃. The fine grain reduced the crack sensitivity of the doped coatings and promoted the transformation of θ-Al₂O₃ to α-Al₂O₃. Therefore, the internal oxidation of the coatings and the growth rate of the oxide films were reduced. The segregation of Sm at grain boundary inhibited the outward diffusion of Ti, thus reducing the excessive oxidation of Ti. In addition, the oxidation mechanism of the coating was changed from simultaneous diffusion of Al and O to predominant inward diffusion of O. The oxidation resistance of the doped coatings was significantly improved. However, excessive Sm₂O₃ is detrimental to the improvement of the oxidation resistance. The oxidation resistance of 3 wt% Sm₂O₃ is the best.