查看更多>>摘要：In this study, different bias strategies were designed for the investigation of the influence of the bias patterns on the mechanical and tribological properties of highly hydrogenated a-C:H films. A series of a-C:H films were made using reactive magnetron sputtering, under several deliberately designed bias patterns. Film hardness and elastic modulus, structure and tribological properties were evaluated using nanoindentation, Raman spectroscopy and rotational ball-on-disk tribological tests. In particular, a quasi in-situ X-ray photoelectron spectroscopy (XPS) technique (vacuum tribo-test to XPS analysis without breaking vacuum) was used in this study. Results showed that low hardness and high CoF could co-exist with low wear rate for a-C:H films. Moreover, no clear relationship between the degree of graphitisation of the transfer film and the tribological properties of a-C:H films could be established. In addition, increased film hardness does not inevitably lead to better wear resistance. It may in fact lead to a much higher wear rate of the counterpart material, hence reducing the life of the tribo-pair as a combined system. The study also provides insights on the effects of biasing strategy on the tribological properties of highly hydrogenated a-C:H films, which would further improve the design quality of preparation parameters of such films.
查看更多>>摘要：The assessment of adhesion property of thin films by scratch test method is still a big challenge, relying on understanding accurately the material response and failure modes during scratch. In this study, a model TiN film on stainless steel substrate was studied by carrying out scratch tests. The entire scratch tracks were observed cross-sectionally and by superficial analysis to characterize its adhesion properties, scratch failures, and material response. Other than cracks and ploughing wear, a series of microscopic deformations and fracture mechanisms were observed and formed the overall material response of the model TiN/substrate system. These responses included substrate plastic deformation, synergistic bulge deformation at the scratch track edge, pile-up in front of the stylus, and fragmentation of TiN film. The spallation failure at the edge of track, where the first spallation was generally assigned as critical load (Lc) Lc2 and features an adhesive failure, was found to be cohesive failure. Furthermore, the Lc3 site corresponded to cohesive failure in the substrate rather than the adhesive failure of the film peeling off completely. Therefore, the results of this study indicate more care should be paid in terms of using Lc to interpret the adhesion properties of other film/substrate systems. The adhesion of film should be evaluated by considering the whole film/substrate system, not solely superficial analysis of the film surface.
Carvalho, IsabelLima, M. JoseNobre, DavidMarques, S. Mariana...
13页
查看更多>>摘要：Diabetic foot is one of the most serious complications of diabetes, the appearance of foot ulcers is highly susceptible to the prevalence of infections. In this sense, thin films of silver (Ag) and silver oxide (AgOx) were deposited by the dc reactive magnetron sputtering technique on different leather substrates for application in insoles and/or footwear inside in order to functionalize them, thus promoting antibacterial properties. A detailed characterization is described to the uncoated and coated leathers. Cytotoxicity and antimicrobial activity were evaluated and, a silver antimicrobial mechanism was suggested. Among the uncoated and coated leathers, AgOx modified samples have higher CoF indicating that this coating can permit higher immobilization of the foot in relation to the skin. The AgOx coating has also impressive antibacterial and antifungal activity without causing any cytotoxic effect, suggesting the potential application of AgOx modified leathers to diabetic specialized footwear.
查看更多>>摘要：Discharge phenomena in electrolytes were discovered many decades ago. However, the research and develop-ment of plasma oxidation in electrolytes for surface engineering have only truly been actively performed in recent years, particularly stimulated by a review paper entitled Plasma Electrolysis for Surface Engineering published in 1999. Among plasma electrolysis processes, plasma electrolytic oxidation (PEO) caught the most attention from academic and industrial communities. However, PEO has been largely restricted to valve metals, such as Al, Mg and Ti and their alloys. This research intends to explore the current boundaries of the PEO process and extend it into non-valve metals. The paper therefore first describes the coating growth mechanisms in non -valve metals, which are different from the conventional PEO (conversion) process on valve metals. Particular emphasis is given to revealing details of the coating deposition behavior through direct observations and analysis of non-valve metallic substrates and their coatings formed at different timescales of the PEO process. Copper and ferrous materials are chosen as appropriate non-valve metal substrates and their coating properties in terms of mechanical, corrosion, thermal and electrical aspects are summarized. The results show that high hardness and adhesion strength, high corrosion resistance, good thermal and electrical insulation performances are achievable for PEO-derived coatings on non-valve metals. These properties also open doors for emerging applications, for example in electrical vehicles. Such applications are presented by reporting the coating application on an e -motor bearing and brake disc as two examples. Future research perspectives are discussed with a hope to stir a new wave of PEO research for non-valve metals as realized by the first review paper for the previous wave of plasma electrolysis research.
查看更多>>摘要：MoSi2 usually suffers pesting failure at 400- 700 degrees C due to severe oxidation of Mo, which has been a great hindrance for industrial applications. To address this issue, this work grew MoSi2(Si) thin films via magnetron cosputtering of a Si single element target and a MoSi2 compound target on Si wafer substrates at room temperature, followed by annealing at 950 degrees C in an argon atmosphere. The as-annealed thin films were heated in a muffle furnace at 700 degrees C in air to experience different duration of oxidation. After that, the oxidation resistance was evaluated by examining the thickness, morphology, structure and composition of the as-heated thin films using field emission scanning electron microscopy and X-ray diffraction, respectively. In comparison with the MoSi2 without doping of Si, the MoSi2(Si) film is denser and exhibits a C11b crystalline structure with a smaller crystal size of 30 nm. The oxidation of Mo is effectively inhibited. There is no big bulge on the film surface after 1 h oxidation. But the oxidation of Si is severe, resulting in the continuous growth of grey SiO2 layer which help preventing the further oxidation of Mo. SiO2 islands are observed after oxidation for 9 h. The early pesting sites gradually become healed by the grown SiO2 layer during oxidation for 60 h. The mechanism for suppressing the pesting failure of MoSi2 by Si doping is discussed in details. A model is developed to explain the process.
查看更多>>摘要：Direct-current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) were used to deposit understoichiometric Ti(1-x)Al(x)B(2-y )diboride coatings by sputtering from a segmented TiB2-AlB2 target using Ar and Kr as sputtering gas. For films with a fixed Al/(Ti + Al) ratio of x = 0.1 (Ti0.9Al0.1B2-y), the B content was varied with y & ISIN; (0.1, 0.6 and 0.7). For films with a fixed y = 0.7 (Ti1-xAlxB1.3), the Al content was varied with x & ISIN; (0.1, 0.4 and 0.7). Evaluation of the mechanical properties of the Ti1-xAlxB1.3 samples showed a reduction in both hardness and elastic modulus with increasing Al concentration, while the Ti0.9Al0.1B2-y samples showed a hardness increase with decreasing B content. Thus, Ti0.9Al0.1B1.3 films exhibited a superior hardness of 46.2 +/- 1.1 GPa and an elastic modulus of 523 & PLUSMN; 7 GPa, compared to the values for Ti0.9Al0.1B1.4 and Ti0.9Al0.1B1.9, showing a hardness of 44 +/- 1 GPa and 36 +/- 1 GPa, and an elastic modulus of 569 +/- 7 GPa and 493 +/- 6 GPa, respectively. The oxidation behavior of the mechanically most promising Ti0.9Al0.1B2-y sample series was investigated through air-annealing at 600 C for durations from 1 h to 10 h. All films formed a mixed non-conformal Al2O3-TiO2 oxide scale which acts as an inward and outward diffusion barrier, significantly reducing the oxidation rate compared to TiBz films, which form an oxide scale consisting of porous TiO2. The thinnest oxide scale after 10 h was found in the B-deficient samples, Ti0.9Al0.1B1.3 and Ti0.9Al0.1B1.4, at ~200 nm, which is significantly below that for Ti0.9Al0.1B1.9 at 320 nm. The enhanced oxidation resistance of highly understoichiometric films is due to the elimination of the B-rich tissue phase that is present at the grain boundaries for higher B content, where the latter has been shown to enhance the rate of oxidation in borides.
查看更多>>摘要：The working condition of the disc cutter of the tunnel boring machine (TBM) is extremely harsh and is severely worn during the rock-cutting and tunneling process. Reducing the wear rate of the cutter and extending the service life of the cutter are essential to improving the economic costs and safety of the TBM. This article explores the feasibility and effectiveness of using surface coatings to improve the wear resistance of the cutter ring. NiCrBSi/WC coatings with different current intensities were prepared on the disc surface using plasma surfacing technology. The wear performance of the coating was evaluated using a bespoke impact-sliding device that fits the actual working conditions, and the wear mechanism was studied in detail. According to the "tadpole-like " wear scar characteristics of the coating after the impact-sliding wear experiment, the wear scar zone can be divided into two regions: the impact region and the sliding region, which are consistent with the actual wear characteristics of the cutter ring. In addition, the wear behavior of the coating noticeably changed under each experiment parameter, and the evolution process of the impact-sliding wear of the gage cutter at each position can be well reproduced. When the impact angle was 45, the wear depth and wear volume of the coating were significantly smaller than those of the uncoated samples. This is mainly due to the metallurgical bond between the Ni-based alloy zone (binder phase) and the spherical WC particles (hard phase) on the surface of each specimen. When impacted by the tribo-ball, the WC particles can undergo plastic deformation and relaxation through the Ni-based alloy zone under the applied force, thereby obtaining excellent impact and sliding resistance. When the impact angle was 60, the impact dominates, causing the impact force to increase. Furthermore, compared with the uncoated specimens, the wear depth and wear volume of the coated specimens significantly increased, indicating that the anti-impact ability was seriously degraded in such situation. In summary, the powder composition and preparation process parameters should be reasonably selected according to the impact angle, and the impact-sliding wear experiment can effectively evaluate the impact and sliding wear performance of different coatings. This approach has an important directive function in the promotion and application of cutter ring coatings.
查看更多>>摘要：The reversible semiconductor-to-metal transition of vanadium dioxide (VO2) makes VO2-based coatings a promising candidate for thermochromic smart windows, reducing the energy consumption of buildings. We report on transfer of the sputter technique for deposition of strongly thermochromic ZrO2/W-doped VO2/ZrO2 coatings on ultrathin (0.1 mm) flexible glass from a laboratory-scale device with three (V, W and Zr) planar magnetron targets to a large-scale roll-to-roll device with two (W-doped V and ZrO2) rotatable magnetron targets. The depositions were performed at a relatively low substrate surface temperature (330-350 degrees C) and without any substrate bias voltage. The W-doped VO2 layers were deposited using a reactive high-power impulse magnetron sputtering with a pulsed O-2 flow control. We compare the process parameters used in both deposition devices and explain the basic principle of this sputter technique using the discharge characteristics measured during a large-scale roll-to-roll deposition. We characterize the design, structure (X-ray diffraction) and optical properties (spectrophotometry and spectroscopic ellipsometry) of the three-layer coatings. The coatings prepared on ultrathin flexible glass using the large-scale roll-to-roll device at a temperature close to 350 degrees C exhibit a low transition temperature of 22 degrees C, an integral luminous transmittance over 45% and a modulation of the solar energy transmittance approaching 10%. This is a promising first step to a cost-effective and high-rate preparation of large-area thermochromic VO2-based coatings for future smart-window applications.
Gudmundsson, J. T.Fischer, J.Hinriksson, B. P.Rudolph, M....
15页
查看更多>>摘要：The ionization region model (IRM) is applied to model high power impulse magnetron sputtering (HiPIMS) discharges with a Cu target. We apply the model to three discharges that were experimentally explored in the past, or applied to deposit thin copper films, with the aim to quantify internal plasma process parameters and thereby understand how these discharges differ from each other. The temporal variation of the various neutral and ionic species, the electron density and temperature, as well as internal discharge parameters, such as the ionization probability, back attraction probability, and ionized flux fraction of the sputtered species, are determined. We demonstrate that the Cu+ ions dominate the total ion current to the target surface and that all the discharges are dominated by self-sputter recycling to reach high discharge currents. Furthermore, the ion flux into the diffusion region is dominated by Cu+ ions, which represents roughly 80% of the total ion flux onto the substrate, in agreement with experimental findings. For the discharges operated with peak discharge current densities in the range 0.9 - 1.3 A cm-2, the ion back-attraction probability of the Cu+ ion (beta t) is low compared to previously investigated HiPIMS discharges, or in the range 44 - 50%, while the ionization probability (alpha t) is in the range 61 - 69%, and the ionized flux fraction is in the range 32 - 40%. It is, furthermore, found that operating these Cu HiPIMS discharges at lower working gas pressures (in the present case around 0.5 Pa) is beneficial in terms of optimizing ionization of the sputtered species.
查看更多>>摘要：Infantile failures of rolling bearings in large-scale wind turbines have limited the reliability of these clean energy generation systems. The major components of a modular wind turbine nacelle include the mainshaft that connects the blade assembly to the gearbox, and the generator. Bearing failures in the components have been attributed to fretting (or false brinelling), smearing, electric arc damage and surface- and subsurface-initiated fatigue. Two surface engineering technologies have been widely employed to address the infantile failures of the rolling bearings: black oxide surface treatments and a W-DLC coating. The specific rolling bearing applications where these technologies are being used in large-scale wind turbines and their effectiveness at mitigating the various tribological issues that cause the infantile bearing failures are described in this paper.
NSTL
Elsevier