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：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.
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：Oxidants, such as oxygen, cannot easily approach the core Al due to the presence of dense alumina on the surface of aluminum particles, thereby resulting in high ignition temperature and long ignition duration. To overcome this challenge, we employed the solvent/non-solvent method using Viton A (a copolymer of 1,1-difluoroethylene and hexafluoropropylene) as a coating material to prepare the core-shell Al/Viton A composite particles. An orthogonal experiment was designed to identify the optimal preparation parameters by evaluating the peak pressure in a closed vessel. The sample with the largest peak pressure was compared with raw Al and Al/Viton A (prepared by the physical mixing method) using the combustion pressure and open combustion tests to evaluate the solvent/non-solvent method. The results from the orthogonal experiment revealed that the water bath temperature exhibited the greatest influence on the coating effects. The composite prepared under a water bath temperature of 55 degrees C and a stirring rate of 250 rpm, using 20 mL of acetone and a 5 mL/min dripping rate of the Viton A acetone solution, were uniformly coated by Viton A, and exhibited excellent combustion characteristics. In addition, the sample generated using the optimal preparation parameters burnt more vigorously and rapidly than raw Al and Al/Viton A. Finally, the reaction molecular dynamics simulation was employed to gain insight into the effect of Viton A on the combustion of Aluminum particles at the molecular level.
查看更多>>摘要：In this paper, bainitic railways were repaired designedly by laser cladding repairing method with AerMet100 steel powder as raw material. The microstructural evolution of repaired specimens was studied carefully, and the corresponding mechanical properties and wear resistance were compared to verify the feasibility of this method. Results show that the bainite microstructures formed in the AerMet100 repaired region exhibit a high microhardness of 515 HV due to high-alloyed solution strengthening and microstructure refinement. The thermal cycles during the repairing process lead to the microstructures in HAZ changing with the distance from the fusion line, and the bottom of HAZ consisting of tempered bainite becomes the microhardness valley. Tensile tests indicate that the overall mechanical properties of repaired specimens are comparable to the bainitic substrate. Compared to the bainitic matrix, wear tests present that the wear resistance of the AerMet100 repaired region is better with the mass loss decreasing by about 28%. The current experimental results suggest that laser cladding repairing with AerMet100 steels is suitable for high-performance repairing of high-strength bainitic steels.
查看更多>>摘要：Titanium (Ti) alloys show excellent fatigue and corrosion resistance, high strength to weight ratio, and no toxicity; however, poor osseointegration ability of Ti may lead to implant loosening in vivo. Plasma spraying of hydroxyapatite [HA, Ca-10(PO4)(6)(OH)(2)] coating on Ti surfaces is commercially used to enhance osseointegration and the long-term stability of these implants. The biological properties of HA can be improved with the addition of both cationic and anionic dopants, such as zinc ions (Zn2+) and fluoride (F-). However, the hygroscopic nature of fluoride restricts its utilization in the radiofrequency (RF) plasma spray process. In addition, the amount of doping needs to be optimized to ensure cytocompatibility. We have fabricated zinc and fluoride doped HA-coated Ti6A14V (Ti64) to mitigate these challenges using compositional and parametric optimizations. The RF induction plasma spraying method is utilized to prepare the coatings. Multiple parametric optimizations with amplitude and frequency during the processing result in coating thicknesses between 80 and 145 um. No adverse effects on the adhesion properties of the coating are noticed because of doping. The antibacterial efficacy of each composition is tested against S. aureus for 24, 48, and 72 h, and showed that the addition of zinc oxide and calcium fluoride to HA leads to nearly 70 % higher antibacterial efficacy than pure HA-coated samples. The addition of osteogenic Zn2+ and F- leads to 1.5 times higher osteoblast viability for the doped samples than pure HA-coated samples after 7-days of cell culture. Zn2+ and F- doped HA-coated Ti64 with simultaneous improvements in anti-bacterial efficacy and in vitro biocompatibility can find application in load-bearing implants, particularly in revision surgeries and immune-compromised patients.
查看更多>>摘要：The NiCrAlY, NiCoCrAlY and NiCoCrAlYTa coatings were prepared on a Ni16Cr13Co4Mo alloy by the D-gun spray technique. The hot corrosion behaviors of the coatings were investigated in molten NaCl-Na2SO4 at 800 degrees C through electrochemical measurements including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky plots. The corrosion layers of the coatings were characterized by electron probe micro-analysis (EPMA), auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results showed that all the corrosion layers of the three coatings displayed the electronic structure of n-p heterojunction. However, the NiCoCrAlY coating had the slowest corrosion rate because Co reduced the carrier density of the corrosion layer and improved the corrosion layer resistance (Rl). The Co sulfides effectively inhibited the internal sulfidation. Ta ion could occupy the Al2O3 lattice and increase the carrier density of the corrosion layer. The hot corrosion of NiCrAlY coating was the most severe since the (Cr, Al) sulfides along the Al2O3 stringers promoted the formation of black bumps on the coating.
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 dense and smooth W-ZrO2 coating was prepared by electrodeposition on a copper substrate in Na2WO4-WO3ZrO2 melt at 1173 K. The coatings composition are alpha-W and monoclinic ZrO2, and the content of ZrO2 increased with the increase of current density. The effect of cathode current density on the morphology, microstructure and performance of the coating was investigated in this paper. The microstructure of the coating was a field-oriented texture type, including an equiaxed grain nucleation layer and a columnar grain growth layer. The roughness has the minimum value of 4.783 mu m at 30 mA/cm2, and the maximum value of 8.586 mu m at 60 mA/cm2. Then, the surface roughness dropped to 6.479 mu m at 80 mA/cm2. The surface micro-hardness increased with the current density increasing, and reached the maximum value of 482 HV at 60 mA/cm2. W-ZrO2 coated copper has excellent electrical conductivity and high temperature oxidation resistance at 30 mA/cm2, 40 mA/cm2, and 80 mA/cm2. The electrical conductivity of coatings prepared at 50 mA/cm2 and 60 mA/cm2 is slightly poorer due to their rough surface and strong preferred orientation. Overall, the texture of the composite material is the most influential factor for electrical conductivity. In summary, as the current density increases, the composition, morphology and microstructure of the coatings changes regularly, which further leads to a predictable change in performance.
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.
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