Evolution Of Microstructure And Properties Of Pt-diffused γ-Ni/γ’-Ni₃Al Coatings Irradiated By High Current Pulsed Electron Beam

Preparation of thermal barrier coatings（TBCs）on metal substrates has been considered to effectively improve the high temperature oxidation resistance of hot section components in aviation engine.The thermally grown oxide（TGO）formed by oxidation on the surface of the bond coat（BC）plays an important role in the service life of the TBCs,and the growth morphology of TGO is closely related to the microstructure of the bond coat.It is of great significance to construct the relationship between the microstructure of the bond coat and the morphology of TGO,the top coat（TC）and the properties of TBCs.Based on this,The Pt-diffusedγ-Ni/γ’-Ni₃Al coatings was prepared on single crystal superalloy substrate and then the surface of the bond coat was modified by high current pulsed electron beam（HCPEB）.The effect of HCPEB treatment on the microstructure of the bond coat was analyzed by modern test methods such as SEM,XRD and EBSD,and the correlation between microstructure and high temperature oxidation resistance of the bond coat was established.On this basis,the YSZ top coat was prepared on the bond coat by electron beam physical vapor deposition（EB-PVD）.The effects of the surface morphology of the bond coat treated with HCPEB on the microstructure and high temperature oxidation resistance of the top coat were studied.The details and conclusions are as follows:（1）Preparation and surface treatment of the bond coat.The Pt-diffusedγ-Ni/γ’-Ni₃Al coatings was prepared by electroplating combined with vacuum thermal diffusion treatment,and then the surface of the sample was treated by HCPEB device.The microstructure analysis shows that the shallow surface of the bond coat treated with HCPEB was melted,the surface was filled with many mutually connected bulged nodules.With the increase of treatment times,the surface roughness first decreases sharply and then tends to be stable.Moreover,HCPEB treatment could induce grain refinement in the shallow surface.（2）High temperature oxidation performance test of the bond coat.The transient and isothermal oxidation performance of the Pt-diffusedγ-Ni/γ’-Ni₃Al coatings before and after HCPEB treatment was tested at 1000℃.The results of transient oxidation test show that a thin and irregular TGO was formed on the surface of the original bond coat in the instantaneous oxidation stage,and more Ni,Al oxide particles were formed on the surface.However,a continuous acicular oxide layer was formed on the surface of the bond coat treated with HCPEB.The isothermal oxidation results show that the main component of TGO in the oxidation process of the bond coat before and after HCPEB treatment was Al₂O₃.Compared with the original bond coat,it treated with HCPEB has continuous TGO structure and more uniform thickness in the oxidation process,which could effectively reduce the later oxidation rate and reduce the spalling degree.（3）Correlation analysis between morphology of the bond coat and growth of the top coat and oxidation resistance of TBCs.The 7YSZ coatings deposited on the Pt-diffusedγ-Ni/γ’-Ni₃Al coatings before and after HCPEB treatment by EB-PVD.On this basis,the isothermal oxidation test of TBCs was carried out at 1100℃.The results show that the columnar crystal size of the top coat grown on the surface of the bond coat treated by HCPEB was small and evenly arranged.With the extension of oxidation time,the TC/TGO interface pores in the original TBCs increased and interface cracks were produced;The thickness of TGO in TBCs treated with HCPEB for 10-pulsed was uniform,and no cracks and other defects were found;When the oxidation time of TBCs treated with 26-pulsed HCPEB was extended to 100h,the top coat spalled.It shows that the bond coat treated with10-pulsed HCPEB has suitable interface morphology and can effectively improve the oxidation performance of TC/BC interface.