Effect of diffusion temperatures on microstructure and properties of NiCoCrAlYHf bond coatings

NiCoCrAlYHf coating （HY5 coating） was prepared on DD6 alloy by vacuum arc ion plating method. After different diffusion temperature treatments， the ceramic coating was deposited by electron beam-physical vapor deposition（EB-PVD） method. The cyclic oxidation properties of thermal barrier coatings at different diffusion temperatures were investigated by analysing the phase composition and microscopic morphology of bond coating（BC） at different diffusion temperatures. The results show that the bond coating samples after diffusion treatment in a vacuum change from the single-phase structure of the deposited to the double-phase structure of the diffusively treated. The content of β-NiAl phase in the bond coating increases with the increase of diffusion temperature. After diffusion treatment， the coating surface is uniform and dense， gray-white and black phases are observed in the coating， the black phase is β-NiAl， and the gray-white phase is γ-Ni and γ'-Ni3Al phases， which demonstrates that diffusion treatment can change the phase structure of the bond coating. The coating with 900 ℃ diffusion treated has the longest cyclic oxidation life， exceeding 400 h； the cyclic oxidation life of 1100 ℃ diffusion treated coating is less than 300 h. When the diffusion temperature is 900 ℃， the oxidation rate of the bond coating and the thermally grown oxide thickening rate are the lowest. It is not that the more β-NiAl phase content the better， but there is a threshold in the phase composition， increasing the β-NiAl phase content within the threshold can obtain better service performance.