Key Engineering Materials Vols. 353-358

Abstract: Sputter deposited SiC films with and without annealing were characterized using X-ray photoelectron spectroscopy (XPS). A complex transition layer, containing silicon oxycarbide (SiCxOy), between the SiO2 layer grown during extended exposure to ambient air or annealing and SiC substrate was investigated. Furthermore, the presence of excessive amorphous carbon was detected in the near-surface region for annealed sample. We justified the differences of composition and chemical bonding in these two oxide layers in terms of different oxidation kinetics involved.

Abstract: Four point bending fatigue tests were carried out using martensitic stainless steel with TiN film deposited at five different deposition rates by dynamic ion mixing process in order to investigate the influence of deposition rate on the fatigue strength. As a result, the fatigue limit clearly increased by the deposition at appropriate conditions. However, the deposition by other conditions resulted in the degradation of fatigue strength. This is caused by the decrease of threshold stress intensity factor after TiN deposition and the difference of defect distribution in the film. In addition, the crack propagation rate was increased in low stress intensity factor range by the deposition of TiN film.

Abstract: Stainless steel is widely used as a corrosion-resistant material. However, stainless steel corrodes at high temperature (573 K ~) due to the oxidization and grain boundary corrosion. To delay the oxidation at high temperature, coating of gas barrier film will be useful method. The purpose of this study is to improve the corrosion-resistant of SUS304 at high temperature by coating transparent SiOxNy film which has gas barrier properties. In addition, the influence of inlet gas mass flow rate ratio (N2/Ar+N2) on the oxidation properties at 773 K was examined. The SiOxNy films were deposited onto polished SUS304 by unbalanced dc magnetron sputtering apparatus. To examine the oxygen transmission rate (OTR) of SiOxNy films, PET was also used as substrate. The results showed that good OTR was obtained for N2/Ar+N2 < 0.12 on PET substrate. The similar tendency was obtained for SUS304 deposited film heated up to 773 K.

Abstract: Boron-doped diamonds were deposited by microwave plasma chemical vapor deposition (MPCVD) method in order to investigate the influence of inlet boron concentration on the film properties. The substrate material of the specimens was pure titanium (99.9 %). Boron source was introduced into the vacuum chamber by bubbling of B2O3, acetone and methanol mixture. Samples were produced with different B2O3 concentrations in mixture (1000 ppm, 5000 ppm, and 10000 ppm). The surface morphology of the samples was observed by scanning electron microscope (SEM). X-ray diffraction was used to identify crystal structures of the films. Secondary ion mass spectroscopy was used to examine the qualitative boron contents in the films. For low B2O3 concentrations in liquid mixture (1000 ppm), the surface morphology of the film showed both micro crystalline diamond and nano crystalline diamond. For medium B2O3 concentrations in liquid mixture (5000 ppm), the surface morphology of the film was also consisted of micro crystalline diamond and nano crystalline diamond. However, the content of micro crystalline diamond decreased in comparison with low B2O3 concentration. For high B2O3 concentration in liquid mixture (10000 ppm), the surface morphology of the film was almost dominated by nano crystalline diamond. Therefore, the crystal size of boron doped diamond decreased with increasing boron concentration. From these results, it appears that boron will restrain the growth of diamond crystal during deposition.

Abstract: Scratch tests were carried out to examine the influence of gas pressure during ion bombarding on adhesion between CrN coatings and aluminum alloy using nitrogen and argon gas. The critical load clearly increased with increasing the nitrogen gas pressure. However, argon gas pressure hardly affected the critical load. The result of SIMS showed that ion bombardment in nitrogen gas generated high Cr content layer at the aluminum substrate surface and the Cr content increased with increasing the pressure. The ion bombardment in argon gas generated low Cr content surface layer and the pressure hardly affected the critical load. Thus, the high Cr content layer by ion bombardment in the high nitrogen pressure improved adhesion between CrN coatings and aluminum alloy

Abstract: Sputtering rate Sr was proposed as an alternative parameter instead of sputtering yield Y to calibrate the sputtering ability of the target, defined as the mass loss of the target per unit time and sputtering current. The approach is more reliable for glow discharge processes since the intense backscattering effect was taken into consideration. The effects of processing parameters on Sr were investigated through orthogonal test, the results indicated that target temperature affects Sr obviously, and among the discharge parameters, the target voltage and discharge pressure were the governing factors. Through regression analysis, the sputtering rate Sr was expressed as a function of sputtering voltage and discharge pressure which could be used to evaluate or predict the real output of the sputtering target.

Abstract: The paper discusses structure and property aspects of oxide films formed on 7075 aluminum alloys by microarc oxidation in alkali-silicate electrolytic solution. Microstructure, surface morphology and phase composition of the ceramic coatings were investigated by SEM and XRD. Distribution of hardness along the coating thickness was determined by microhardness analyses. The friction and wear behavior of the oxide films against steel counterparts was evaluated with a friction and wear tester. The results showed that the microarc oxidation coatings composed mainly of α-Al2O3 and γ-Al2O3 phase are dense and uniform, which indicates that the wear resistance of Al alloy could be improved obviously by microarc oxidation. The films possess a beneficial combination of 25~45 μm thickness, HV0.11500 microhardness and provide a low wear rate but a relatively high friction coefficient against GCr15 steel under dry friction condition.

Abstract: A Mo-Si-C-N multi-layer anti-oxidation coating was in situ fabricated on C/C composites by fused slurry and reaction-sintering method in nitrogen atmosphere using Mo and Si element powders, and characterized by X-ray diffractometry, optical microscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy with energy dispersive spectroscopy. It is shown that the coating contains three distinctive layers, namely, SiC inner-layer, MoSi2/Si middle-layer and Si3N4/SiC/Si thin surface-layer. The MoSi2/Si middle-layer, whose thickness could be controlled by dipping process, is the main portion of coating. Oxidation test reveals that the Mo-Si-C-N multi-layer coating significantly improves the oxidation resistance of the C/C composites. Compared with the Mo-Si-C coating, the oxidation temperature is extended up to 1450°C. After oxidation pre-treating at 1400°C, the anti-oxidizing temperature of the Mo-Si-C-N multi-layer coated C/C composites can be raised to 1500°C and the weight loss is less than 1wt% after 12-hour oxidizing test.

Abstract: To improve adhesion of DLC coatings, Fine Particle Bombardment (FPB) treatment using Cr based shot particles was performed. After the FPB treatment, DLC coating process was generated on the Chromium-molybdenum steel. The FPB treatment distributes diffused Cr elements onto the treated surface, creating a Cr-rich layer. The FPB treatment increases the surface hardness and roughness which also affect the adhesion of DLC coatings. Wear test was conducted to compare the tribological properties of the DLC coated FPB treated steels and that of the DLC coated non FPB treated ones. The DLC coated surface, after FPB treatment, kept low friction coefficient, while the DLC coated non FPB treated ones showed a sudden increase due to the delamination of DLC layer. These results imply that delamination of the DLC coating was suppressed by the Cr-rich surface layer created by the previous FPB treatment. Consequently, the applied method was effective to improve the adhesion of DLC coatings.

Abstract: Electric contact is an important component of high voltage circuit breaker switch lubicle, isolating switch and ground switch. It is composed of arc-extinction end and conduction end. The usual material of arc-extinction end is copper-tungsten and the usual material of conduction end is copper or chrome-copper. Currently, four process for making the integral electric contact such as common brazing, vacuum brazing, electric-beam welding; liquid-phase sintering is of the best integral technique capability. This article puts forward a process by friction welding for integral Cu-W electric contact, and studies about the weldability between copper-tungsten and copper or chrome-copper, and between copper and chrome-copper. In order to solve the worse weldability between copper-tungsten and copper or chrome-copper, the design conception of intermediate layer is tentatively suggested. From experimental results, using the production method of friction welding is practicable to integral electric contact. It has some advantages, such as high availability of material, high productivity, high ratio of finish products, and it has no any influence on environment.