Effect of the thickness on properties of Al2O3 coatings deposited by plasma spraying

Al2O3 coatings with different thicknesses (160, 320, 480 and 640 μm) were deposited on stainless steel substrate by plasma spraying. The variation in microstructural characteristics and properties of coatings with various thicknesses was investigated. Powders morphology and the microstructure of as-sprayed coatings were characterized by scanning electron microscopy and optical microscopy. The microhardness was measured using a Vickersʹ indentor. The corrosion behaviour of plasma-sprayed Al2O3 coatings in 1 N H2SO4 solution at a temperature of 25 °C was evaluated by electrochemistry method. Experimental results indicated that surface roughness showed no obvious dependence on the coating thickness. However, the porosity of Al2O3 coating was increased with increased thickness. The enhanced coating thickness also resulted in decreasing microhardness and reduced corrosion resistance. In this study, the Al2O3 coating with thickness of 160 μm possesses the lowest porosity, the highest hardness and superior corrosion resistance.