Microstructure and Properties of Thermal Sprayed ZrO 2 -NiCr Coatings

NiCr/ZrO2 gradated coatings were obtained on C45 carbon steel by high velocity arc spraying and micro-plasma spraying to improve the mechanical and thermal behaviors of the carbon steel. Scanning electronic microscope (SEM) and X-ray diffraction (XRD) were employed to characterize the microstructure of the prepared composite coatings. Mechanical properties including hardness and bonding strength were also evaluated by microhardness tester and electron tensile tester. The thermal shock behaviors were investigated by quenching the coating samples in cold water from 900 °C and 1100 °C, respectively. The oxidation of NiCr/ZrO2 gradated coating and C45 carbon steel substrate were carried out for up to 108 hours in air atmosphere at 1100°C. The oxidation behaviors were investigated after detailed examinations by thermal gravimetric analysis. Experimental results indicate that NiCr/ZrO2 gradated coating exhibit a much higher hardness and high temperature oxidation behavior than the substrate. The bonding strength and thermal shock behavior of NiCr/ZrO2 are superior to pure ZrO2 coating, which could be mainly attributed to the NiCr intermediate graded layer due to the microstructure improvement and relaxation of residual stress concentration.