Abstract: ZrO₂ coating was prepared on the surface of Q235 steel substrate by supersonic plasma spraying technology (SAPS). Microstructure, phase composition and element distribution of the ZrO₂ coating were detected and analyzed by scanning electron microscope (SEM), energy spectrometer (EDS) and X-ray diffractometer (XRD), respectively, and the hardness of the ZrO₂coating was measured by Vickers hardness tester, and the hardness of the coating, the coating-substrate junction and the substrate were obtained respectively. The results show that there are a large number of grain bulges and holes in the surface of the coating prepared by SAPS. The longitudinal section of the coating has transverse cracks and pores in the shape of horseshoe, meniscus, ellipsoid and irregular polygon, and the porosity is 13%. The Zr element diffuses in the coating at high temperature and the content of Zr increases from the top to the bottom of the coating, and a small amount of Zr element appears on the surface of the substrate. The coating material undergoes a phase change from a monoclinic phase to a tetragonal phase during the spraying process. The microhardness of the coating, the coating-substrate junction and the substrate is 740.51, 205.79 and 189.33 HV0.2, respectively, and the microhardness of the coating-substrate junction is increased compared with that of the substrate.

Key words: supersonic plasma spraying, ZrO₂, microstructure, microhardness