| ?-(Ni,Pt)Al coatings as a high-temperature protective coating,possess a good combination of oxidation and corrosion resistance,so they are widely applied on the key components in hot sections of advanced aero engines and land-based turbine engines.However,the coating is subject to high-temperature oxidation and thermal corrosion during the service process,and the coating will degrade or fail after a certain period of time;at the same time,in the process of coating,the preparation quality of the coating is not qualified due to various factors.Due to the complicated manufacturing process of the blade,and the preparation cost of the blade itself is much higher than that of the coating.Therefore,if the failure and unqualified coatings can be effectively removed,this will be of great significance to the processing of unqualified products during the blade preparation process and to extend the service life of single crystal superalloy blades.In this work,?-(Ni,Pt)Al coating was prepared on nickel-base superalloy by gaseous aluminisation treatment.The feasibility study of chemical removal of the coating was carried out,and finally the removal process of the coating was determined and the coating was refurbished.The XRD,SEM,EPMA and other analytical methods were used to investigate the characterization of the superalloy substrates after the coating removed and the refurbished coatings.The microstructure of the substrate surface and the refurbished coating were investigated.The oxidation and interdiffusion behavior of the refurbished coating were studied.The main research contents and results are as follows:(1)A single-phase(Ni,Pt)Al coating was removed by soft chemical stripping method.In the process of coating removal,the coating was effectively removed by reaction with Ni Al phase and corrosion along grain boundary,and the secondary reaction zone was retained in the matrix after removal.(2)The microstructure of the refurbished coating was similar to that of the virgin coating,but TCP phase still exists in the matrix below the coating.The content of Al and Pt at the interface between the coating and matrix was higher than that of the original coating,while the content of Ni was opposite.(3)The interdiffusion behavior of refurbished coating between the coating and the substrate was alleviated effectively in the oxidation process.(4)The oxidation kinetics of the virgin coating and refurbished coating at 1100°C were investigated.In the early stage of oxidation,the oxidation increase of the refurbished coating was greater than that of the virgin coating,but with the extension of oxidation time,the oxidation gain of the virgin coating exceeded that of the refurbished coating.When the refurbished coating was oxidized at high temperature,dense and continuous Al2O3 oxide film can be formed on the surface,which exhibited improved isothermal and cyclic oxidation resistance than the virgin one,slowing the oxidation rate and reducing the surface rumpling. |
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