Papers by Author: Heng Ji

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: Plasma sprayed hydroxyapatite (HA) coatings on titanium alloy substrates have been used extensively due to their excellent biocompatibility and osteoconductivity. However, the low bonding strength between HA and Ti substrates is still problematic in the long-term implantation lifespan. In this paper, HA/Ta composite coatings with various Ta contents (20% and 60%) were fabricated by vacuum plasma spraying (VPS). The microstructure, phase composition of the coatings was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results revealed that the coatings had a rough surface and lamellar structure including some pores. ASTM C-633 standard was used for the measurement of bonding strength, which was found increasing with the increase of Ta contents in the composite coatings. The bonding strength of the composite coating containing 60% Ta (H4T6) reached to 37.2 MPa, which is about 1.9 times that of HA coating. In vitro bioactivity evaluated in simulated body fluids (SBF) showed that bonelike apatite layer was formed on the composite coatings surface, which indicated the good bioactivity of the HA/Ta composite coatings.

Abstract: Tungsten is one of the most promising candidates for the plasma facing materials (PFM) in fusion experiment devices. In this study, tungsten coatings were fabricated on copper alloy substrates via air plasma spraying technology. The in-flight behaviors of tungsten particles in the spraying process were investigated. The microstructure and some properties of the as-sprayed coatings, including surface roughness, bonding strength, microhardness and thermal property, were evaluated. The results showed that the temperature and velocity of the in-flight tungsten particles increased by enhancing the spraying power. Un-melted particles and microcracks were found for the coatings prepared under the low (32.7kW) and high (47.6kW) spraying powers, respectively. The highest bonding strength and microhardness were obtained for the coating prepared under a medium spraying power (42.5kW) by reason of its good in-flight behaviors. The thermal conductivity of tungsten coatings was 32.2 W٠K-1٠m-1 at room temperature, which was much lower than that of bulk tungsten.

Abstract: Silicon-based materials have been widely applied in industrial fields, such as microelectronic and solar power, for the specific electronic properties. In the present work, free-standing thick silicon coatings were fabricated by air plasma spraying (APS) and vacuum plasma spraying (VPS) technologies. The microstructure and electrical property of the coatings were characterized. It was found that the electrical resistance of APS-Si coating was higher than that of VPS-Si coating. The impedance spectroscopy results showed there was significant difference in impedance curves of APS-Si and VPS-Si coatings. The grain boundary semicircle appeared in the plot of VPS-Si coating, while did not appeared in that of APS-Si coating. It was thought that the electrical property difference of the two kind coatings was related with the oxidation and microstructure difference of the coatings.

Abstract: The W coatings were prepared by applying the vacuum plasma spraying process (VPS). The phase composition, microstructure and laser irradiation property were characterized by XRD, SEM and laser. Results showed that no tungsten oxide appears in the coatings whose phase composition is similar to the original powder. A better melting state of the coating can be obtained by using the finer powder. The deposition efficiency of the coating is higher in the cases of a higher H2 flow. There is a pitch whose size is about 100μm when the substrate was irradiated by laser. However, there is clearly no change for the W coating surface which was also irradiated under the same condition. It indicates that the laser irradiation resistance is improved significantly for stainless steel after being deposited with W coating.