Effect of critical plasma spray parameters on the microstructure, microhardness and wear and corrosion resistance of plasma sprayed alumina coatings

Plasma sprayed ceramic coatings are successfully used in many industrial applications, where high wear and corrosion resistance with thermal insulation are required. Plasma sprayable alumina powders with γ- and α-forms have been prepared by chemical precipitation route by varying the calcination temperatures of the powders and without the spray drying step. The powders are characterized by scanning electron microscopy, powder X-ray diffractometry, particle size analysis and flowability. The alumina powders are plasma sprayed at three different critical plasma spray parameters (CPSP; 675, 825 and 937.5 W/nLpm). In the present work, the influence of CPSP values on the crystallographic forms of alumina, microstructure, microhardness, surface roughness and wear behavior of the coatings is investigated. Plasma sprayed alumina coating with a CPSP of 825 shows higher wear and corrosion resistance compared to other coatings. The coatings are subjected to thermal cycling at 1100 °C and coatings plasma sprayed at lower and moderate CPSPs are intact even after 700 thermal cycles. Also, the effect of starting phases (α and γ-alumina) on the preferential orientation of [113] of the plasma sprayed coating is studied as a function of CPSP.