Papers by Author: Gu Liu

Abstract: 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.

Abstract: Al2O3 coatings were fabricated by multi-functional micro-plasma spray through axial powder feed. The flight particle velocity and temperature were measured by SprayWatch-2i. With the rising of Ar flow, the velocity of Al2O3 particles increases, but the temperature of particles decreases gradually. Al2O3 coatings were analyzed by SEM and XRD. The microstructure of coatings is density, low porosity and uniform morphology. X-ray diffraction results show that α-Al2O3 is the main phase in the original Al2O3 powders, but Al2O3 coatings consist of γ-Al2O3 and a small amount of α-Al2O3. The microhardness and bonding strength of Al2O3 coatings were also measured, which is HV0.11183~1387 and 28.6MPa, respectively.