1 College of Mechanical and Energy Engineering, Shaoyang University, Shaoyang 422000, Hunan, China 2 Key Laboratory of Hunan Province for Efficient Power System and Intelligent Manufacturing, Shaoyang University, Shaoyang 422000, Hunan, China
The core-shell structured CoNiCrAlY-Al2O3 powders were well-designed and fabricated with the Al2O3 as the shell. The ball milling preparation process of core-shell structured powders was optimized by orthogonal experiment design. The phase structure and microstructure evolution of the high velocity oxy-fuel sprayed(HVOF) CoNiCrAlY-Al2O3 coatings caused by using of core-shell structured powders were discussed. The oxidation behavior of HVOF CoNiCrAlY coating and CoNiCrAlY-Al2O3 composite coating at 800 ℃ was comparatively studied.The results show that the influence of the process parameters on the average coating rate of the core-shell structured powders in descending order are: ball milling rotation speed, mass ratio of ball to powder and ball milling time.The optimal ball milling parameters for preparing CoNiCrAlY-Al2O3 core-shell structured powders are: ball milling rotation speed of 180 r/min, mass ratio of ball to powder of 10∶1, and ball milling for 6 h. The HVOF CoNiCrAlY coating is mainly composed of γ-Co-Ni-Cr phase.The oxidation behavior of CoNiCrAlY alloy during spraying process is significantly inhibited by the using of core-shell structured raw powders. Due to the existence of the high melting point Al2O3 shell in the raw powders, the CoNiCrAlY-Al2O3 composite coating contains a high content of β-NiAl phase. In addition, the coating has high porosity and high content of un-melted particles.Compared with CoNiCrAlY coating, CoNiCrAlY-Al2O3 composite coating has excellent high temperature oxidation resistance. The high content of β-NiAl and Al2O3 in the composite coating leads to the formation of a dense Al2O3 rich protective layer on the surface of the coating during high temperature oxidation. The oxide film significantly inhibits the growth of non-protective oxides.
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