Manufacture Of Al₂O₃-MgAl₂O₄Multilayer Coating By APS And Its Dielectric Properties

The purpose of this work was to improve the dielectric properties of Al₂O₃coating.The Al₂O₃-MgAl₂O₄multilayer composite gradient coating was fabricated by air plasmaspraying on the substrate of copper. The feed powders were Al₂O₃and mechanical mixedpowder of Al₂O₃and MgAl₂O₄with the mass ratio of50:50,70:30and90:10. Differenttest methods which were EDS, SEM and X-ray diffraction were used to characterize themicrostructure, compositions and phases of the coatings. Residual stress, hardness,bonding strength and porosity were examined. Broadband dielectric spectroscopy wasused to detect the dielectric properties. DC breakdown voltage was analyzed by dielectricstrength tester.The results show that composite coating has a well bond and typical lamellarstructure, the Al₂O₃deposits were the γ-Al₂O₃metastable structure, while the MgAl₂O₄shows the spinel stable structure. Tensile test showed that the failure mode was cohesivefailure. The distribution of coating microhardness conformed to Weibull analysis results.The range of coatings porosity was tested by image analysis method and the porosity ofAl₂O₃-50wt.%MgAl₂O₄composite coating is9.36%, Al₂O₃-30wt.%MgAl₂O₄compositecoating is3.17%, Al₂O₃-10wt.%MgAl₂O₄composite coating is5.96%and Al₂O₃coatingwas3.87%. The surface residual stress analysis results reveal that the residual stress ofmultilayer structure is lower than that of bilayer structure obviously. What’s more, theresidual stress between composite coatings is pressure stress which could improve theresistance property.Al₂O₃-MgAl₂O₄multilayer composite gradient coatings show excellent dielectricproperties. The dielectric constant and dielectric loss of composite coatings demonstratethe similar change trend following the temperatures and frequencies. The dielectric loss isless than0.2under the frequency range of0～10MHz and the temperature range of25～300℃. Particularly, the DC breakdown voltage of Al₂O₃-MgAl₂O₄multilayer compositegradient coating reached up to8.5kV and increased by32.86%after sealing. In conclusion, Al₂O₃-MgAl₂O₄multilayer composite gradient coating presentedexcellent dielectric properties.