Effect of critical plasma spray parameter on complex permittivity and microstructure by plasma spraying Cr/Al2O3 coatings

Highlights: ► Deposit the Cr/Al2O3 coatings for microwave absorbing application. ► We study the effects of CPSP on the complex permittivity. ► Increasing CPSP content enhance the complex permittivity. ► The reflection loss varies with changes of coatings thickness and Fe amount. - Abstract: In this paper, Cr/Al2O3 coatings formed via a plasma spray approach with different critical plasma spray parameters using Al2O3 and Cr powder feeds were prepared. The effects of CPSP on the phase composition, microstructure, complex permittivity, porosity and adhesive strength of the coatings were investigated. The microstructure and phase composition of coatings were examined using scanning electron microscope (SEM) and X-ray diffraction (XRD). XRD analysis reveal that Cr, γ-Al2O3 and α-Al2O3 are found in all the coatings, and percentage of γ-Al2O3 is increased due to complete melting of the particles and their consequent rapid solidification. The experimental results have shown that the CPSP condition has significant influence on the microstructure and complex permittivity of the coatings. Both the real part (ε′) and imaginary part (ε″) of relative complex permittivity are increased with improving the CPSP condition.