Effect of critical plasma spray parameter on complex permittivity and microstructure by plasma spraying Cr/Al ₂ O ₃ coatings

In this paper, Cr/Al ₂ O ₃ coatings formed via a plasma spray approach with different critical plasma spray parameters using Al ₂ O ₃ 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-Al ₂ O ₃ and α-Al ₂ O ₃ are found in all the coatings, and percentage of γ-Al ₂ O ₃ 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.