Papers by Keyword: Vacuum Plasma Spray

Abstract: ZrB₂-SiC-WSi₂ (labeled as ZSW) coating and ZrB₂-SiC (labeled as ZS) coating were fabricated by vacuum plasma spray technique. The microstructure and composition of as-sprayed coating were detected through X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray energy dispersive spectrometry (EDS). Oxidation behaviors and microstructure evolution of these coatings were evaluated at 1500 °C in air and compared with ZrB₂-SiC coating. The results showed that the addition of WSi₂ improved the oxidation resistance of the ZrB₂-SiC coating. There was more liquid formed on the ZSW coating surface. Some bubbles were also observed on the coating surface, which might be resulted from gas formation. It can be concluded that the amount of WSi₂ had great influence on its function in ZrB₂-SiC system.

Abstract: ZrC-20vol.%MoSi₂ (ZM) composite coating was fabricated by vacuum plasma spray and the ablation resistance was assessed using plasma flame under low (1.94 MW/m²) and high (3.01 MW/m²) heat fluxes, respectively. Results showed that the ultimate surface temperatures of ZM coating were about 2100 °C and 2400 °C, respectively. ZM coating exhibited good ablation resistance at low heat flux, which benefited from the low evaporation of SiO₂ and the diffusion of Si derived from MoSi₂ decomposition. However, bubble-burst event took place under high heat flux. The different ablation behaviors of ZrC-MoSi₂ coating were analyzed, which might contribute to the application of ultra-high temperature ceramic coatings.

Abstract: In the present work, the light-emitting property of silicon coating was explored and the related morphologies and chemical structure of silicon coating were characterized. Silicon coating was prepared by vacuum plasma spray technique and chemically treated by HNO₃/HF vapor. The coatings before and after the vapor etching were characterized by field emission scanning electron microscopy and micro-raman spectroscopy. The photoluminescence spectra of the silicon coatings treated with different time were examined. It is found that pores of micrometer and microcracks formed on the surface of silicon coatings after the treatment. The treated silicon coatings exhibited room temperature visible photoluminescence with emission wavelength around 650 nm after excitation. The results of micro-raman measurement proved that there were polysilane and oxygen related functional groups appeared on the coating surface after the vapor treatment, which was supposed to be responsible for the photoluminescent phenomena.

Abstract: Hydroxyapatite and silicon-substituted hydroxyapatite powers were prepared in-house through a wet precipitation method and then vacuum plasma sprayed onto Ti-6Al-4V discs. Two plasma gun input powers were employed, 37 kW and 40 kW. All coatings were nearly phase pure, except small traces of impurities (TTCP, -TCP and CaO). Coatings prepared under the lower plasma gun input power had lower crystallinity. In vitro studies showed that human osteoblast-like cells attached and spread very well on all coated discs. Among the four kinds of discs, SiHAC37 was the most supportive to cell growth.

Abstract: Bond coatings, CoNiCrAlY, are prepared on Inconel 738 substrate by vacuum plasma spray (VPS). Mechanical properties of VPSed CoNiCrAlY coatings are investigated via Taguchi method and L18(21×37)
orthogonal arrays to determine the optimal setting and the relationship of experimental variables. Seven parameters were considered as follows: (A) arc current; (B) primary gas flow rate; (C) secondary gas flow rate; (D) stand-off distance; (E) working pressure; (F) carrier gas flow rate (Ar); and (G) powder feeding rate.
The effect of carrier gas flow rate on the porosity is determined to be the highest among the parameters investigated. Higher microhardness values are observed for the VPSed coatings as compared to the coatings prepared by conventional high velocity oxygen fuel probably due to low amount of the porosity.