| In this paper,coatings were prepared on the surface of K17 and Inconel 600 high temperature Ni-based alloy substrates by electrophoretic deposition technique and vacuum sintering process,respectively.The oxidation resistance of the NiCoCrAlY coatings,the element diffusion and phase evolution of the bond layer and K17 matrix during the oxidation process were studied.The phase composition,bonding strength,high temperature oxidation resistance and electrochemical corrosion resistance of the YSZ and YSZ/(Ni,Al)coatings were also studied.NiCoCrAlY coating prepared by electrophoretic deposition and vacuum two-step sintering,using absolute ethanol as the suspension and adding AlCl3·6H2O as the additive.AlCl3·6H2O was decomposed into Al2O3 during the two-step vacuum densification process.Al2O3 as a binder wrapped with the metal powder particles which made the coating more uniform and compact.Ni3Al,Ni and(Ni,Co)Al phases exist on the NiCoCrAlY bond coating.The thickness of NiCoCrAlY bond coating is about 30?m.Al and Cr were diffused to the coating surface to form dense oxide film during the oxidation test at 1000?.NiCoCrAlY coating had a protective effect on the oxidation at high temperature by oxidation weight gain analysis.The YSZ/(Ni,Al)composite thermal barrier ceramic coatings were prepared by doping Al and Ni in YSZ ceramic powders.These cracks made the coatings exhibit a network-like structure,which reduces the thermal expansion coefficient mismatch of the coatings and the matrix.The bond strength and oxidation resistance of YSZ/(Ni:Al=1:1)ceramic coating is better than others.The thickness of YSZ/(Ni:Al=1:1)ceramic coating is about 45?m.The coating of oxidation at 1100?for 40 h is the most compact,it is due to the formation of?-Al2O3,which filled with the gas holes.The formation of?-Al2O3 is very compact,can effectively prevent the diffusion of oxygen to the inside of the coating and reduce the oxidation rate.Therefore,the effect of coating self-healing is best after oxidation for 40 h.After oxidation to 60 h,the pores emerged again in the interior of the coating,this is because that NiCr2O4phase(brittle spinel structure)within the coating was produced.The YSZ/(Ni,Al=1:1)coating of oxidation for 40 h has the highest Ecorr(-221mv,vs SCE),the lowest Icorr(5.01×10-8A cm-2),the highest breakdown voltage(532 mV),and the maximum value of the impedance in the low frequency region compared with YSZ/(Ni,Al=1:1)coatings of other oxidation time. |
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