查看更多>>摘要：The deposition of functional coatings for various purposes on internal surfaces of devices and equipment is highly requested in a wide variety of production areas. In the electric power industry, there is a problem of combining a copper-aluminum contact pair in the conical terminals of vacuum switches with the possibility of providing a low contact resistance and a high tightening torque or compression force, respectively. In this work, it is proposed to use high-energy plasma spraying for reliable combining copper and aluminum by Cu plasma spraying onto the inner conical Al contact surfaces. For this, a unique configuration of a high-energy plasma accelerator has been developed, which ensures producing and uniform spraying of Cu material in a single short-term working process (less than 1 ms). The dependence of the amount of deposited Cu material on the value of the specific supplied energy has been established to ensure the deposition of coating with a thickness not less than 40 mu m and porosity from 3 to 8%. Also, the process implementation at increased supplied energy is found to provide the Cu and Al combination with a fourfold decrease in the contact resistance in comparison with the classical method of their connection. In addition, the high-energy plasma spraying results in forming an intermediate layer between copper coating and aluminum substrate containing intermetallic phases of Al4Cu6 and Cu3Al2. This layer is characterized by increased microhardness (up to 6-12 GPa) and provides high adhesion (more than 2000 MPa) due to hydrodynamic mixing of Cu and Al.
查看更多>>摘要：The tetrahedral amorphous carbon (ta-C) coating is one of the fascinating surface coating for superior mechanical properties. Although its outstanding mechanical strength, it is hard to achieve adhesion stability due to high interfacial and residual stresses. Here, we introduce a new concept of pretreatment called large pulsed electron beam (LPEB) treatment. To specify the adhesion of the ta-C coating following the LPEB treatment, various adhesion tests, including the scratch test and Rockwell indentation test, were conducted. Thus, the ta-C coating pretreated with LPEB was found to have excellent adhesion through qualitative and quantitative analyses. Furthermore, to elucidate the mechanism for improving adhesion, analyses were conducted from two aspects: 1) deformation of the substrate and 2) stress change at the interface between the coating and the substrate. As a result, ta-C pretreated with LPEB increased the hardness of the substrate and supported the coating well. In addition, the thermal contraction of the coating was decreased after deposition, reducing the stress between the coating and the interface, and the adhesion was considerably improved.
查看更多>>摘要：Many engineering (biomedical, automotive, aerospace etc.) structures suffer from wear and corrosion damage under service conditions and this situation shortens their useful life. In common cases, these damage mechanisms do not act on materials separately. On the contrary, their combined effect called as tribocorrosion cause more decrease in their lifetime than the individual effects of wear and corrosion. Tribocorrosion damages are directly related to surface properties of materials. In order to improve tribocorrosion performance of materials, different surface modifications were applied to enhance their performance and one of them is shot peening. However, tribocorrosion behavior of shot peened materials have not been clarified so far. Therefore, in this study, the effect of shot peening on the tribocorrosion properties of AISI 4140 low-alloy steel was investigated in detail. AISI 4140 samples were shot peened under different Almen intensities and their tribocorrosion performance were examined. The results revealed that the increasing Almen intensity changed the surface characteristics from hydrophobic to hydrophilic. Also, it was determined that the tribocorrosion performance of the material improved with the increasing shot peening intensity in terms of increased surface hardness.
查看更多>>摘要：In order to enhance the wear resistance of MoNi matrix coatings at elevated temperature, high-temperature wear resistant MoNi matrix coatings with different Cr contents (3.0 wt%, 7.0 wt% and 11.0 wt%) were prepared on the 718 alloy substrate by laser cladding. The high-temperature tribological performance was investigated sliding against Si3N4 ceramic ball by using ball-on-disk tribo-tester from room temperature to 1000 ?. The effects of chromium addition on the microstructure and the tribological performance of coatings were systematically studied. The coatings with dendritic structure consisted of Mo, Cr9Mo21Ni20 and Cr1.12Ni2.88 phases. The coatings showed a good metallurgical bonding interface with the substrate. There was a critical value of Cr content which could best reinforce the high-temperature wear resistance of MoNi matrix coating. The coating containing 7 wt% Cr had the best wear resistance over a wide temperature range, which was due to the in-situ formed salt compounds, high hardness and oxide lubricating film. The wear mechanism of three coatings transferred from the fatigue wear and abrasive wear to the oxidative wear with the increase in testing temperature.
查看更多>>摘要：The surface treatment of Ti80 alloy with different microstructures was performed by laser shock peening (LSP), and the effect of LSP on Ti80 alloy on microstructure and corrosion properties was investigated. After LSP, the surface grains of Ti80 alloy with different microstructures were all refined, micmhardness was significantly increased, and compressive residual stress was generated, and both microhardness and compressive residual stress showed gradient change characteristics along the layer depth. The corrosion resistance of Ti80 alloy with different microstructures was improved in both 3.5% NaCl solution and 5MHCL solution after LSP. Before LSP, the corrosion resistance of lamellar microstructure was the best, followed by bimodal microstructure and the worst by equiaxial microstructure, while the corrosion resistance of equiaxial microstructure exceeded that of bimodal microstructure under the combined effect of volume fraction of beta phase, thickness of alpha phase and compressive residual stress after LSP.
查看更多>>摘要：The paper demonstrates how defects inherited from the deposition processes can severely impair the lifetime of MCrAlY coatings in service. The oxidation behavior of two NiCoCrAlY coatings was investigated at 1150 degrees C up to 500 h. The coatings had the same nominal composition but were processed by two different projection techniques: air plasma spray (APS) and high velocity oxy fuel (HVOF). Freestanding coating specimens were extracted from the coated system and thinned down to different thicknesses ranging from 520 to 15 mu m in order to investigate size effects inherent to the oxidation response. The oxidation rate of the APS coating was found to be insensitive to the specimen thickness, while that of the HVOF coating increased with the specimen thickness, due to greater intersplat oxidation. APS specimens thinner than 60 mu m experienced intrinsic chemical failure (InCF) due to Al consumption to form the Al2O3 scale. In comparison, HVOF specimens with a thickness of 367 mu m were subject to InCF after 250-350 h oxidation. This first stage of InCF resulted in the formation of a Cr2O3 layer at the Al2O3/metal interface once Al activity in the MCrAlY coating was low enough to thermodynamically allow Cr2O3 to form. In addition, thick HVOF specimens developed mechanically induced chemical failure (MICF) resulting in the formation of (Ni,Co)(Cr,A1)(2)O-4 spinels on top of the Al2O3 scale and within oxide intrusions. The occurrence of MICF was associated with the concomitant effects of Al consumption due to intrusive oxidation and the spallation of the external Al2O3 scale.
查看更多>>摘要：Fabricating layered double hydroxides (LDHs) coatings intercalated with corrosion inhibitors is considered an effective strategy for improving the corrosion resistance of metal substrates. However, to our best knowledge, studies applying LDHs coatings modified with ionic liquids (ILs) as environmentally friendly corrosion inhibitors to corrosion protection of metals and alloys have not been reported. In this contribution, two kinds of MgAl-LDHs coatings modified with imidazolium based dicationic ILs, namely LDH-C-6(m(2)im)(2)-I and IL@LDH-C-6(m(2)im)(2)-I, were successfully prepared on AZ31B magnesium alloy. The LDH-C-6(m(2)im)(2)-I coating intercalated with C-6(m(2)im)(2)-I ionic liquid was synthesized by the co-precipitation method and hydrothermal treatment, followed by a facile immersion experiment in a dimethyl sulfoxide solution containing C-6(m(2)im)(2)-PF6 ionic liquid to produce the IL@LDH-C-6(m(2)im)(2)-I composite coating. The surface morphologies and anti-corrosion properties of the two MgAl-LDHs coatings immersed in 3.5 wt% NaCl solution were investigated. The present results reveal that the LDH-C-6(m(2)im)(2)-I coating exhibits a uniform and dense petal-like nanoflowers structure, while the IL@LDH-C-6(m(2)im)(2)-I composite coating contains a compact C-6(m(2)im)(2)-PF6 IL film and a lamellar-structured LDH-C-6(m(2)im)(2)-I, which provides a double corrosion protection to the Mg alloy. As a result, the corrosion current density of IL@LDH-C-6(m(2)im)(2)-I is only thirty-eighth of that of LDH-C-6(m(2)im)(2)-I and 4 orders of magnitude lower than that of bare AZ31B Mg alloy. More importantly, the surface of samples coated with IL@LDH-C-6(m(2)im)(2)-I is still compact without being destroyed after 168 h of immersion, which can be ascribed to the synergistic effect of excellent self-healing and durable corrosion resistance. This work opens a new way of preparing MgAl-LDHs coatings modified with ionic liquids to remarkably enhance the anti-corrosion performance of Mg alloys.
查看更多>>摘要：Exploring tritium permeation barriers with high permeation reduction factor (PRF) by an industrial scale process is crucial for tritium systems in fusion reactors. Herein, we fabricated a dense Fe-Al/Al2O3 coating by a simple hot-dipping aluminizing (HDA) method and optimized oxidation strategy. The microstructure, chemical composition, and crystallographic characteristic of obtained samples were investigated. And the permeation of deuterium through the sample was determined by gas-driven permeation (GDP) experiments. The results show that the obtained oxide coating mainly consisted of gamma-Al2O3 layer and Fe-Al gradient transition layer. Notably, the Al2O3 layer formed by the oxidation of FeAl alloy coating possessed a high PRF value of 2394 at 550 degrees C. Compared with the direct oxidation of HDA sample, the oxide coating prepared by the alloy topcoat oxidation strategy was denser and had less defects. Meanwhile, the effect of Al topcoat and different Fe-Al alloy topcoats on the microstructure and performance of the oxide coating were investigated, respectively. And the formation mechanisms of oxide coatings prepared by different oxidation strategies were also analyzed.
查看更多>>摘要：The corrosion resistance of AZ31 is inappropriate, which demands the improvement of the anti-corrosion performances for practical applications. Therefore, environmentally friendly rare earth elements based such as Ca-Ce and Ca-Y layered double hydroxide (LDH) coatings are developed on the AZ31 alloy surface in this work. The coatings are characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and the static sessile drop method as well as electrochemical measurements. The results show that these two kinds of LDH coating can obviously retard the corrosion of AZ31 in simulated body fluid (SBF). Also, precipitation of the corrosion products synergistically improves the self-healing and protection performances. However, the Ca-Y based layers contain some cracks that limit the superior protection performance of the coating. The Ca-Ce based LDH coating shows a significantly enhanced corrosion resistance with the corrosion current density of 0.058 mu A.cm(-2) which is prepared in the solution containing the Ca and Ce cations with the 2:1 mol ratio. It opens the possibility to improve the service life of AZ31 magnesium alloy in SBF.
查看更多>>摘要：The microstructure evolution of the interdiffusion zone (IDZ), secondary reaction zone (SRZ), and substrate diffusion zone (SDZ) formed beneath the coating/substrate interface in a directionally solidified (DS) nickelbased superalloy during thermal exposure has been investigated. Recrystallization occurred in the substrate below the coating at both 900 degrees C and 1000 degrees C. However, significant differences in the evolution of the SRZ and topologically close-packed (TCP) phases were observed at 900 degrees C and 1000 degrees C. Numerous rode-like a phases precipitated in the gamma'-based cellular recrystallization (CR) zone at 900 degrees C for 100 h. In contrast, after 100 h at 1000 degrees C, a continuous gamma layer was formed in the IDZ and moderate amounts of needle-like a precipitates were found in the SDZ. Furthermore, after thermal exposure for 1000 h at 900 degrees C, the rod-like a-phases within the SRZ gradually dissolved with substantial precipitation of M23C6, and the number of needle-like a-phases increased and grew in size. Nevertheless, after exposure at 1000 degrees C for 1000 h, the SRZ was completely consumed by the IDZ and the needle-like a phases in the SDZ were incorporated with the gamma layer and dissolved progressively.
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Elsevier