Growth and structure of TiCxNy coatings chemically vapour deposited on graphite substrates

TiCxNy coatings were grown on graphite substrates in a computer-controlled, hot-wall chemical vapour deposition (CVD) reactor, using gas mixtures of TiCl4–CH4–N2–H2 at a total pressure of 10.7 kPa (80 torr) and at a temperature of 1400 K. Growth rate, composition, morphology and crystallographic texture of the TiCxNy coatings were investigated as a function of the CH4/CH4+N2 ratio in the range 0–1 at a constant CH4+N2 flow rate of 370 standard cubic centimeters per minute (sccm). The C/C+N ratio and growth rate of the TiCxNy coatings increased with increasing CH4/CH4+N2 ratio in the gas phase. The compositions of the coatings with C/C+N ratios in the range 0–1 were found to be between the thermodynamic and the kinetic predictions. Morphology and preferred orientation of the coatings were observed to be strongly affected by the CH4/CH4+N2 ratio in the gas phase.     

Chemical constitution and microstructure of TiC x coatings chemically vapour deposited on Fe-C substrates; effects of iron and chromium

TiC _x coatings were chemically vapour deposited in an industrial reactor on Fe-C substrates with carbon contents between 0.06 and 1.20 wt % C. Electron probe microanalyses showed that significant amounts of chromium and iron were present in the coatings and that chromium was also present in the substrate region adjacent to the coatings. By comparing calculated and measured lattice parameters (corrected for the internal stresses present) it became evident that the chromium was in solid solution in TiC _x , whereas the iron was not. This was confirmed by micro Auger electron spectroscopy and X-ray diffraction phase analyses. The carbon to metal ratio,x, of the TiC _x coatings decreased with increasing distance to the coating/substrate interface. The effect of iron on the X-ray diffraction line broadening and hardness of the coatings was large (in contrast with the effect of chromium) and increased with increasing distance to the coating/substrate interface because of a decreasing iron particle size. The TiC _x crystallite size was small and constant throughout the thickness of the coatings. The chromium present in the substrate region adjacent to the TiC _x coatings influenced the microstructure of the substrate by formation of iron, chromium-carbides and reduced the growth rate of the coatings.     

Development and partial relaxation of internal stresses in thin TiC layers chemically vapour deposited on Fe-C substrates

TiC layers were chemically vapour deposited at 1273 K mn Fe-C substrates with carbon contents between 0.06 and 1.20w%C. X-ray diffraction stress analyses showed that large compressive stresses are present in the IC coatings and that small tensile stresses any present in the substrates. The stresses developed during cooling from the deposition temperature to room temperature, owing to the difference in thermal shrink between coating and substrate. However, stress relaxation was also evident. This was provoked by the phase transformation processes occuring in the substrate on cooling. Stress relaxation was hindered when grain-boundary cementite formed in the substrates. The stresses present in the TiC coatings on substrates without grain-boundary cementite can be predicted quantitatively.     

Plasma-enhanced chemical vapour deposition of AlN coatings on graphite substrates

Graphite substrates have been covered with aluminium nitride (AlN) layers prepared by plasma-enhanced chemical vapour deposition from AlBr₃-N₂-H₂-Ar gas mixtures. The glow discharge (frequency, 13.56 MHz; power, 50–500 W) was generated by an r.f. induction coil. The graphite substrate mounted on a grounded graphite susceptor was inductively heated up to a temperature in the range 200–800 °C. The mass of the deposit per square centimetre was determined as a function of reaction time, total gas pressure, substrate temperature, r.f. power, gas flow velocity and AlBr₃ concentration. The morphology of the AlN layers was examined by scanning electron microscopy. Fine-grained polycrystalline AlN films were grown at 700 °C under a total pressure below 10 Torr. Translucent polycrystalline AlN films having a 〈001〉 preferred orientation were deposited at a total pressure in the range 10–40 Torr.     

Creep of chemically vapour deposited SiC fibres

The creep, thermal expansion, and elastic modulus properties for chemically vapour deposited SiC fibres were measured between 1000 and 1500°C. Creep strain was observed to increase logarithmically with time, monotonically with temperature, and linearly with tensile stress up to 800 MPa. The controlling activation energy was 480 ± 20 kJ mol^–1. Thermal pretreatments near 1200 and 145O° C were found to significantly reduce fibre creep. These results coupled with creep recovery observations indicate that below 1400°C fibre creep is anelastic with negligible plastic component. This allowed a simple predictive method to be developed for describing fibre total deformation as a function of time, temperature, and stress. Mechanistic analysis of the property data suggests that fibre creep is the result of -SiC grain boundary sliding, controlled by a small percentage of free silicon in the grain boundaries.     

Study of growth rate and failure mode of chemically vapour deposited TiN,TiCxNy and TiC on cemented tungsten carbide

The effects of deposition temperature and mole ratio of CH₄ to TiCl₄ on the growth rate of titanium compound coatings were investigated. Activation energies of TiN, TiC _x N _y and TiC deposition reactions of 4.8×10⁴, 1.9×10⁵ and 2.8×10⁵ J mol^–1, respectively, were obtained experimentally. The carbon content of TiC _x N _y deposit was increased as the CH₄ flow rate and deposition temperature increased. It was found that TiC _x N _y grain size was finer than TiC and TiN.The cutting temperatures of TiN-coated and TiC-coated tools were 10% (TiN) and 20% (TiC) lower than that of uncoated tools. Feed force and reaction force of coated tools were 30% and 18% less than those of uncoated tools, respectively. The dominant failure mode of coated tools was due to the microchipping of the cutting edge.     

Structural investigation of silicon films chemically vapour deposited onto amorphous SiO2 substrates

The influence of substrate temperature and the silane-to-nitrogen ratio on the structure of silicon films 0.5–0.6 μm thick deposited onto amorphous SiO₂ substrates was investigated by X-ray diffraction. The investigations were carried out for silicon films deposited at various temperatures in the range 500–750 °C and with various silane-to-nitrogen ratios in the range 3.04 × 10^-4-2.84 × 10^-3 by volume. The silicon films deposited at 500 °C were amorphous while the films deposited at 550 °C were randomly oriented polycrystalline. The films deposited in the temperature range 600–700 °C were polycrystalline with a preferred orientation that changed from 〈110〉 through 〈100〉 to 〈111〉. The structure of the films deposited at 750 °C was randomly oriented polycrystalline. Investigations of the influence of the silane-to-nitrogen ratio on the silicon film structure revealed that the structure of films deposited at a substrate temperature of 500 °C was independent of the silane-to-nitrogen ratio. The structure of the films deposited at 600 °C depended on the silane-to-nitrogen ratio and changed from polycrystalline with a 〈110〉 preferred orientation to randomly oriented polycrystalline when the ratio was increased. The structure of films deposited at 700 °C also depended on the silane-to-nitrogen ratio and changed from randomly oriented polycrystalline to polycrystalline with double preferred orientation (〈100〉 and 〈111〉) when the ratio was increased.     

Inter-diffusion of carbon into niobium coatings deposited on graphite

The inter-diffusion of carbon (originating from a graphite substrate) into a niobium coating and the fabrication of its carbides by heat treatment in the temperature range of 1073-1773 K was studied. The thickness of the Nb₂C and NbC phases formed after heat treatment as well as the inter-diffusion coefficients for the formation of the carbide layers were also studied. It was found that the carbide layer growth displayed parabolic behavior patterns inherent in the growth rate constants (K) of Nb₂C and NbC layers.By assuming that the inter-diffusion coefficients are independent of concentration, it was possible to determine the inter-diffusion coefficients of carbon D^c into Nb₂C and NbC layers as a function of temperature.     

Structure of chemically vapour deposited silicon carbide for coated fuel particles

The silicon carbide coating layers prepared under various conditions were examined by density measurement, X-ray diffractometry, and optical and scanning electron microscopies in order to clarify the relation between deposition conditions and structure of the coating layers. It was found that the deposition temperature was the main parameter affecting the content of free silicon, density, crystallite size and lattice distortion, and microstructure. The dependence of these properties on the coating rate and the composition of fluidizing gas was not observed clearly. Free silicon was co-deposited with-SiC at temperatures lower than 1400 to 1500° C, and the content of free silicon increased with decreasing deposition temperature. The density of the layers without free silicon was more than 3.210 Mg m^–3 and the density decreased with increasing content of free silicon. Crystallite size increased with deposition temperature and lattice distortion decreased with increasing deposition temperature. The outer surfaces of the layers without free silicon consisted of large interlocked grains, whereas those of the layers with free silicon showed a cauliflower-like structure of which the apparent grain size was small.     

Adhesion of TiC and TiN coatings prepared by chemical vapour deposition on WC-Co-based cemented carbides

Adhesion energies of CVD-prepared TiC and TiN coatings on WC-Co-based cemented carbides are determined on the basis of an energy formulation of the scratch test. Values found for the adhesion energyW areW _TiC=10 J m^–2 andW _TiN=46 J m^–2.     

聚碳酸酯表面铬酸预处理对涂层附着性能影响

聚碳酸酯材料表面呈惰性,不利于涂料的完全润湿和界面化学键的结合.为增强聚碳酸酯材料表面的涂层流平性能和附着性能,本文利用铬酸湿化学方法对聚碳酸酯透明材料进行表面预处理,测试预处理前后聚碳酸酯的表面能、元素组成、表面形貌以及应力-溶剂银纹,研究预处理对聚碳酸酯表面性能的影响.结果表明,铬酸的强氧化作用使聚碳酸酯表面产生了羰基、磺酸基及羧基3种含氧极性基团,增加了基材表面粗糙度和润湿性能.通过拉开法和涂层/基材界面扫描电镜两种方法比较了铬酸预处理对耐磨涂层附着性能的影响,研究发现,受涂层与PC之间界面共价键及机械锚接作用力,预处理后涂层附着性能明显增强.涂层附着力与铬酸处理时间密切相关,而较长时间处理会降低PC表面抗应力-溶剂银纹性能,实验表明在不损失材料抗银纹性能前提下,铬酸预处理5 min可以显著提高涂层附着力.     

Mechanical buckling instability of thin coatings deposited on soft polymer substrates

Deformation of rubber and poly(ethylene terephthalate) coated with a platinum or a gold film was studied. The thickness of the coating film was approximately ten nanometers. The polymer substrates were 10⁴ to 10⁵-fold softer than the coating. Folding of the coating leading to the appearance of a wave-like pattern on an originally smooth surface was observed both in tension and after shrinkage. In tension the wave crests are oriented along the elongation direction. After shrinkage the wave crests are perpendicular to the shrinkage direction. For rubber substrates, the appearance of the wave is explained by a mechanical buckling instability of the coating under compressive force. The length of the surface wave depends on the thickness of the coating layer and the rigidity of the polymer substrate. In addition to folding, regular fragmentation of the coating film on long and comparatively narrow bands is observed. The cracks are perpendicular to the wave crests both in tension and after shrinkage.     

TiC coatings deposited onto carbon and molybdenum surfaces by electron beam evaporation

TiC coatings were deposited onto graphite and molybdenum substrates by an electron beam evaporation method. A titanium film 1000–10000 Å thick was evaporated onto the graphite substrate which was then heated at 1000 °C for 5 min to form the TiC film by an interdiffusion process. In the case of the molybdenum substrate, a double-layer film consisting of titanium and carbon (Ti/C/Mo) was prepared by evaporation and the subsequent heat treatment was performed at 700 °C or at 1000 °C for 5 min. The properties of the coatings were examined by various surface analysis techniques including Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Rutherford backscattering (RBS). The atomic ratio of carbon to titanium in these coatings was found to be 0.9. The in-depth profiles obtained by XPS examination showed that the coating prepared at 700 °C had a carbon layer between the TiC layer and the molybdenum substrate, while that prepared at 1000 °C had an Mo₂C layer between the coating and the substrate.     

Influence of substrates on the structural and optical properties of chemically deposited CdS films

Cadmium sulfide (CdS) films were chemically deposited on glass, polycarbonate (PC), polyethylene terephthalate (PET), and Si wafer. Effects of substrate types on the structural and optical properties of the films were investigated. There is a preferential orientation of the crystallites in the film grown on the glass along the c-axis (perpendicular to the plane of the substrate) producing a strong hexagonal (0 0 2) or cubic (1 1 1) peak, regardless of the presence of ITO coating. However, such preferential orientation decreases or disappears when the deposition was made onto PC or PET substrates. The crystallinity of CdS films on glass and Si is better than that of the other ones. The average transmittance of the films on PC and PET is about 50% and 55%, respectively, and increases up to 70% for glass substrate. The improvement of the transmittance was obtained from ITO-coated substrates.     

The effect of boron on the microstructure and physical properties of chemically vapour deposited nickel films

The solid solution addition of boron greatly enhances the strength and hardness of chemically vapour deposited (CVD) nickel while dramatically changing the microstructure. The solid solubility of boron in nickel is limited, and single-phase alloys containing in excess of 0.3 at% B are supersaturated with respect to the formation of one or more intermetallic boride phases. Single-phase Ni-B alloys containing 0 to 13.0 at% B were produced by CVD on polycrystalline copper substrates at 155° C in an atmospheric pressure process. The microstructure, mechanical and physical properties were characterized for the alloys both as-deposited and after various thermal treatments by using optical microscopy, transmission electron microscopy, X-ray diffraction and micro-indentation hardness testing with a diamond pyramid indentor. The grain size of the alloy was found to decrease sharply with rising boron content. Concomitantly, the defect density of the material rose significantly, the microhardness increased and the ductility decreased. With annealing at a temperature of 300° C or greater, precipitation of the Ni₃B intermetallic phase, recovery and grain growth occurred.     

Wet chemical deposited ITO coatings on flexible substrates for organic photodiodes

ITO (tin doped indium oxide) coatings were produced by gravure printing process on PET and PEN foils. The printing paste consists of ITO nanoparticles, which are dispersed in a solvent and mixed with a binder. By modification of the printing paste, the sheet resistance (R/sq) of the ITO coatings after hardening under UV-irradiation at low temperatures (< 130 °C) could be decreased to 1 kΩ/sq. R/sq could be further reduced down to 0.5 kΩ/sq by heat treatment under forming gas atmosphere (N₂/H₂), the transmission of the ITO coated foils still being more than 80% in the visible range. The application of these ITO films as a bottom electrode in organic photodiodes (OPDs) is shown, and the current density-voltage characteristics of the OPDs are presented.     

Optical and structural properties of chemically deposited CdS thin films on polyethylene naphthalate substrates

CdS thin films were deposited on polyethylene naphthalate substrates by means of the chemical bath deposition technique in an ammonia-free cadmium-sodium citrate system. Three sets of CdS films were grown in precursor solutions with different contents of Cd and thiourea maintaining constant the concentration ratios [Cd]/[thiourea] and [Cd]/[sodium citrate] at 0.2 and 0.1 M/M, respectively. The concentrations of cadmium in the reaction solutions were 0.01, 7.5 × 10⁻³ and 6.8 × 10⁻³ M, respectively. The three sets of CdS films were homogeneous, hard, specularly reflecting, yellowish and adhered very well to the plastic substrates, quite similar to those deposited on glass substrates. The structural and optical properties of the CdS films were determined from X-ray diffraction, optical transmission and reflection spectroscopy and atomic force microscopy measurements. We found that the properties of the films depend on both the amount of Cd in the growth solutions and on the deposition time. The increasing of Cd concentration in the reaction solution yield to thicker CdS films with smaller grain size, shorter lattice constant, and higher energy band gap. The energy band gap of the CdS films varied in the range 2.42-2.54 eV depending on the precursor solution. The properties of the films were analyzed in terms of the growth mechanisms during the chemical deposition of CdS layers.