Effect of alumina addition on the microstructure properties of plasma-sprayed zirconia-alumina coatings

ZrO2/Al2O3 coatings with different amounts of Al2O3 were fabricated on the AISI 304 stainless steel surface using plasma spray process. Phase composition and microstructure of the coatings were characterised using X-ray diffraction and scanning electron microscopy. Lamellae and porous microstructure were obtained in the coatings. In addition, a small amount of unmelted particles, partially melted, and fully melted regions in microstructure of coatings were observed. With the increasing addition of Al2O3, a decrease in the pores was determined. The results indicated that the as-prepared ZrO2/Al2O3 based coatings were mainly composed of ZrO2, Al0.52Zr0.48O1.74, ZrTiO4, Al0.18Zr0.82O1 91, Al2O3, Al2Zr3, Al3Ti and Ti2O3 phases. The microhardness of the coating was as high as 1136 HV0.2, which was 4-5 times of the substrate.