Research On Active Diffusion Barrier Of Matal Coating On Superalloy

High temperatuer function coating interface evolves in the service process.The interface element diffusion and soild phase reaction in the interface could lead to the rathe coating failure.Diffusion barrier prepared between substrate and coating, has been used widely to restrain the diffusion and reaction in the interface.However,the existing system of diffusion barrier cannot achieve good combination and diffusion resistance at the same time.In this paper, ZrO2pioneer coating and NiCrAl coating are prepared on nickel-based alloys DD5by electron beam physical vapor depotision (EB-PVD). Al2O3active diffusion barrier in the interface between the ZrO2pioneer coating and NiCrAl coating has been formed through controlling the heat treatment atmosphere and temperture.The reaction thermodynamic of Al2O3active diffusion barrier was analyzed.The formation process and the formation mechanism of Al2O3active diffusion barrier Were studied.The degradation process and the degradation mechanism of Al2O3active diffusion barrier in the long-term high temperature oxidation were investigated by using scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS).The results show that:The continuous Al2O3active diffusion barrier which can restrain the element interdiffusion effectively formed in the interface between ZrO2pioneer coating and NiCrAl coating after heat treatment at900℃for5h in vacuum.Thermodynamic calculations showed that Al can react with ZrO2and Ni and Cr cannot react with ZrO2in vacuum. The reaction can be expressed as follows:4Al+3ZrO2→2Al2O3+3Zr.The formation mechanism of Al2O3active diffusion barrier is that Ni, Cr and Al elements of the NiCrAl coating diffuse into the ZrO2pioneer coating, and Al reduces Zr from ZrO2, then the continuous Al2O3active diffusion barrier layer formed in the interface between the ZrO2pioneer coating and the NiCrAl coating. Before forming the complete Al2O3layer, Ni, Cr continue to diffuse into the ZrO2pioneer coating. So there are bits of Ni, Cr, Zr in the Al2O3active diffusion barrier layer. The degradation mechanism of Al2O3active diffusion barrier after long-time oxidation is that the oxygen elements diffuse into the interface between the ZrO2pioneer coating and the NiCrAl coating, and react with impurity elements of Ni and Cr in the Al2O3active diffusion barrier layer. The oxides destroy the continuity of Al2O3layer, and a large number of NiO and NiAl(Cr)2O4form, leading to the comletely degradation of Al2O3active diffusion barrier. The Al2O3active diffusion barrier degradate into Ni oxide-based mixed oxide.