Microstructure and cyclic oxidation of a Hf-doped (Ni,Pt)Al coating for single-crystal superalloys

A diffusion-barrier-contained Hf-doped (Ni,Pt)Al coating was prepared by firstly composite electroplating and then aluminising. The TEM study of the microstructure showed that Hf serves as a solid solution in (Ni,Pt)Al lattice and forms HfO2 in the Hf-rich zone. This HfO2 is formed in situ during aluminisation under low oxygen pressure. It acts as a diffusion barrier to prevent the inter-diffusion during cyclic oxidation. In comparison with (Ni,Pt)Al coating, the oxide scale on Hf-dope (Ni,Pt)Al is more adherent. Moreover, the surface rumpling extent is much relieved due to slower Al depletion rate and higher creep resistance by Hf addition.