Effect of initial particle size on microstructure and dielectric properties of Cr/Al2O3 coatings deposited by plasma spraying

Cr/Al2O3 coatings were deposited by low-power plasma spray technology using spray-dried feedstock powders with different sized initial Cr particles. XRD results revealed that c-Al2O3 phase formed in the process of plasma spraying. The effect of initial Cr particle size on the microstructure was investigated. It was found that the coatings deposited with larger initial Cr particles possessed denser structure and lower porosity, and the Cr clusters in these coatings were more prone to form due to the connections of adjacent metal lamellae. Moreover, the initial Cr particle size had a significant effect on the dielectric properties. The complex permittivity of as-sprayed Cr/Al2O3 coatings was evidently enhanced with increasing initial Cr particle size, which was attributed to the interfacial polarization and the formation of metallic conductive clusters.