The deposition of platinum coatings by double glow plasma technique on titanium alloy substrates at different gas pressures is reported. The corrosion properties of platinum coatings were investigated. The coating deposited at gas pressures of 20 and 30 Pa had a preferred (220) orientation due to the initial nuclei with preferred growth on the surface of the substrate. The coating deposited at gas pressure of 25 Pa showed no evidence of preferential orientation. The platinum coatings showed better corrosion resistance than the titanium alloy. The electrochemical properties of the platinum coatings deposited at different gas pressures had some difference because the porosity in the coating increased with increasing gas pressure.
Si 3 N 4 ceramic matrix composites reinforced by carbon fibres (C f /Si 3 N 4 ) were prepared by low pressure chemical vapour infiltration at 1250uC using SiCl 4 and NH 3 as precursor. The as prepared C f /Si 3 N 4 composites were ablated to determine the mechanism of the ablation resistance and oxidisation resistance by oxyacetylene torch at 2200uC. The morphology and microstructure of the composites were examined by scanning electron microscopy. The phase compositions of the composites were confirmed by energy dispersive X-ray spectroscopy and Xray diffraction. The results indicated that the matrix of the C f /Si 3 N 4 composites was composed of the amorphous Si 3 N 4 and nanometre a-Si 3 N 4 . A central ablation region and a ring oxidisation region appeared on the surface of the as ablated C f /Si 3 N 4 composites. Sublimation of the Si 3 N 4 matrix and oxidation of the carbon fibres are the main ablation behaviours in the central region. Oxidation of the Si 3 N 4 matrix and deposition of SiO 2 particles are the main ablation behaviour in the ring region. A large number of SiO 2 liquid droplets produced during ablation were retained and formed spherical solid particles on the surface of the ring region after ablation. For the mismatch of the coefficient of thermal expansion of the carbon fibres and the Si 3 N 4 matrix, Si 3 N 4 matrix was cracked under the thermal impact of the oxyacetylene flame. With the passive oxidation of the as cracked surface, the continuous SiO 2 liquid was formed in the ring region. Subsequently, some residual Si 3 N 4 particles were covered by transparent SiO 2 layer to form an amber-like microstructure.
Dense and uniform Iridium (Ir) coating was deposited on the surface of the graphite substrate by double glow plasma. The phase identification and the morphology of the coating were examined by X-ray diffraction and scanning electron microscopy, respectively. The coating was composed of uniformly distributed regularly conical aggregates which were composed of the columnar crystals with a preferential (220) orientation. The preferential orientation was regardless of different deposition parameters and substrate properties. The analytic equation of the generatrix of the conical aggregate was determined by measuring its external dimensions. The deposition rate of the coating was up to 20 mm h 21 . The gap appeared within the fracture surface of the coating could result from the shadow effect of the conical aggregate. Because of the poor wetting between Ir element and C element, Ir coating grew according to the Stranski-Krastanov model.
Dense and uniform coatings of iridium (Ir), 5-7 mm in thickness, were deposited onto molybdenum (Mo) substrates by double glow plasma discharge in the temperature range of 800-850uC at 35 Pa. During deposition, the Mo substrate was biased at a voltage of 2300 V while the 99?9% Ir target was at a bias voltage of 2800 V. After deposition, the Ir coating was ablated using an oxyacetylene torch with a flame temperature of y2000uC to determine the high temperature stability of the coated substrate. The morphology and microstructure of the Ir coating were observed using scanning electron microscopy while the composition and structure were measured using X-ray diffraction and energy dispersive spectroscopy. The thickness of the as deposited Ir coating was uniform and the interface between the coating and the substrate exhibited excellent adhesion with no evidence of delamination and cracks. After exposure to the flame, the surface of the as ablated coating presented imperfections including pores, bulges and cracks; however, the Ir coating retained sufficient adhesion to limit the weight loss of the Ir coated Mo substrate to 10 mg cm 22 s 21 .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.