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Manufacture of Al2O3-MgAl2O4Multilayer Coating by APS and Its Dielectric Properties

Author: YangYingChun
Tutor: LiangBo
School: Yanshan University
Course: Materials Science
Keywords: APS multilayer composite gradient coating Al2O3-MgAl2O4 dielectricproperties DC breakdown voltage
CLC: TG174.4
Type: Master's thesis
Year: 2013
Downloads: 1
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Abstract


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.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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