查看更多>>摘要：Micro-arc oxidation (MAO) is an effective approach to control the corrosion rate of magnesium and its alloys. The multi-porous structure of the MAO coating, however, can result in the infiltration of the corrosive medium into the inner regions of the coating, and the corrosion resistance deterioration. In this study, a tantalum oxide (Ta2O5) was prepared on MAO-coated pure Mg to seal the micropores. The composite coatings were characterized by SEM, EDS, XRD, XPS, and TEM. And then the degradation behavior of the samples was investigated by electrochemical experiments and in vitro degradation tests. Results demonstrate that Ta2O5 effectively closes the micro defects in the MAO coating and plays a role of physical barrier. Compared with the uncoated sample, the current density of the MAO/Ta2O5 composite coating was reduced by three orders of magnitude. In addition, the values of pH, and weight loss were also significantly reduced during in vitro immersion tests. Further, the corrosion resistance mechanisms of MAO/Ta2O5 coating were also suggested. During the immersion process, the solution penetrates the sample surface through some microdefects, resulting in the chemical reaction between the destructive solution and the sample, and in turn, improving the local degradation of the sample. As a result, inhomogeneous corrosion occurs on the surface of the composite coated sample and is accompanied by the deposition of Ca and P. These results indicate the excellent protective properties of the MAO/Ta2O5 composite coating.
查看更多>>摘要：Aluminum alloys (Al alloys) are susceptible to corrosion due to their high chemical activity, particularly in complicated marine surroundings. Liquid-repelling Al alloy surfaces with enhanced corrosion resistance were prepared via a facile one-step chemical etching and modification with 1H,1H,2H,2H-Perfluorodecyltriethoxysilane. Results indicated that the fabricated sample with step-like micro/nanostructures exhibited excellent superamphiphobicity, which the static contact angles achieved 162?degrees, 158?degrees, and 152 for water, ethylene glycol, and hexadecane, respectively. Furthermore, electrochemical tests shed light on that the superamphiphobic surface fabricated greatly improved the anti-corrosion performance and durability of the substrate in 3.5 wt% NaCl aqueous solution. The whole process requires no special equipment, providing a facile and environment friendly method to fabricate superamphiphobic surfaces.
查看更多>>摘要：Shot peening is a widely used surface strengthening technique which can improve the fatigue life of metal components by introducing reasonably distributed compressive residual stress. The accurate prediction of re-sidual stress distribution of parts is a tough challenge in the simulation of shot peening. In this paper, the nu-merical calculation of the residual stress of shot peening is investigated with 12Cr2Ni4A steel as the target. A two-dimensional Gaussian distribution model is proposed to calculate the number of impact shots. A method is proposed to calculate shot peening coverage using displacement and displacement gradient, which increases the identification accuracy of peened surface topography and provides a scientific method for coverage calcu-lation. A random multi-shot finite element model for high strength steel is established considering the elasto-plastic of shot. The effects of the process parameters, initial surface morphology and initial residual stress on the residual stress distribution after shot peening are investigated. The accuracy of the proposed method is verified by comparing the measured and simulated results.
查看更多>>摘要：Mo, as a typical refractory element in Ni-base superalloys, will diffuse outward to the protective coating on the alloy surface during high-temperature oxidation, which will do harm to mechanical properties of the alloy and oxidation resistance of the coating. In this paper, (gamma' + beta) two-phase Ni-34Al-0.3Dy coatings with or without Pt were prepared on a single crystal superalloy with high Mo content by electron beam physical vapor deposition (EB-PVD) and Pt electroplating. The short-term oxidation behavior of the coatings was investigated at 1100 ?degrees C aiming to explore the role of Dy and Pt on the harmful effect of Mo diffusion and its oxides. The results show that for Pt-free coating, Mo had already diffused to the coating surface after only 1 h. The pre-existing Dy2O3 would react with MoO3 to form Dy2MoO6 thus suppressed the volatilization of MoO3 at the early stage of oxidation. However, as the oxidation proceeded, Dy2MoO6 would decompose due to its poor thermal stability. While for Pt doped coating, no Mo-rich oxides were detected throughout the entire oxidation process due to the suppression of outward Mo diffusion by the Pt layer at coating/substrate interface. The possible mechanisms were discussed in detail.
查看更多>>摘要：Selective superantiwetting/superwetting nanostructured ZnO/CuO mesh membrane was constructed using a facile method. The ZnO/CuO coated mesh exhibited switchable wettability from superhydrophobic to superhydrophilic properties using annealing treatment at high temperatures. The field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses were applied for characterization. The wettability was determined by water/oil static contact angle (W/OCA) and contact angle hysteresis (CAH). The coated mesh showed superhydrophobic properties without any post-treatment with a water contact angle of 161.2 degrees +/- 1.5 degrees and contact angle hysteresis of 4.2 degrees +/- 1 degrees. The wettability of the surface was altered to superhydrophilicity in air and underwater superoleophobicity (OCA of 162 degrees +/- 2 degrees) after annealing at high temperatures. Evaluation of wetting stability confirmed that the ZnO/CuO surfaces exhibited long-term stability of superwetting properties towards the water after exposure to ambient air due to creating high oxygen vacancies amounts after annealing treatment compared to the ZnO coating. The prepared nanostructured surface was considered to isolate the oil/water mixtures. The results proved that the coated meshes could be applied effectively to separate oil/water mixtures with excellent separation efficiency (> 99.9%) and good flux (above 2000 L m- 2 h-1) regardless of oil density, even in harsh conditions.
查看更多>>摘要：The boron content affects the microstructures and high-temperature tribological performance of AlCrBN coatings. AlCrBN coatings with various B contents (0 at.%, 1.5 at.%, 2.9 at.%, 4.8 at.%,) were synthesized by multi-arc ion plating. The microstructure, mechanical and high-temperature tribological properties were investigated. TEM results show that addition of 1.5 at.% of B results in solid solution (Al, Cr, B)N and a small amorphous a-BNx within the (Al, Cr, B)N columnar structure. Further addition of B contents of 2.9 at.% and 4.8 at.% leads to the composite structure comprising of nano-grains surround by amorphous a-BNx. As the B content increases, the amount of nano-grains decreases, and the thickness of the amorphous layer increases. The hardness measurements also indicate that the AlCrBN coating with 1.5 at.% B content had the highest hardness of 38.3 GPa due to the solution strengthening. On the other hand the AlCrBN coating with 2.9 at.% B content had the best toughness with higher values of H/E (0.073) and H-3/E-*2 (0.169 GPa). High-temperature tribological measurements showed that the friction coefficients decreased with temperature for all such AlCrBN coatings. At 400 degrees C, AlCrBN coatings with B contents of 0 at.%, 1.5 at.%, and 2.9 at.% exhibited low wear rates due to their high hardness, while AlCrBN coating with a B content of 4.8 at.% showed the lower wear rate at 800 degrees C due to the formation of a continuous B2O3/B(OH)(3) film on the coatings.
Vitoriano, J. de O.Pessoa, R. S.Filho, A. de A. MendesFilho, J. de Amorim...
8页
查看更多>>摘要：Currently, the study of oxynitrides surfaces emerges as one of the most promising ways to obtain improvements in several properties of titanium and expand its applications. In this context, the plasma-assisted thermochemical technique has stood out due to its versatility and easy to control precisely the structure and composition of the compound layer. In this work, titanium samples were subjected to 40%H-2-60%N-2 and 40%H-2-45%N-2-15%O-2 plasma treatment for surface modification where the effect of OH species in the oxynitride formation was investigated. Grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy and X-ray induced photoelectron spectroscopy (XPS) were used for structural and chemical composition analyses. Also, optical emission spectroscopy (OES) was used in order to study the plasma chemistry. Results evidenced that the addition of H-2, which consequently increases the concentration of OH species in the plasma, during the pre-treatment and treatment was important for the cleaning and reduction of native titanium oxides. XPS results showed that the titanium surface, which had 92% Ti-O bond before treatment, was totally reduced, giving rise to Ti-N-O (56%) and Ti-N (44%) bonds when nitrided. When oxygen was added to the atmosphere, the Ti-N bond disappeared, giving rise to the Ti-O bond (27%) and Ti-N-O bond (73%). The treatments were suitable for oxynitriding the titanium surface in a predominantly diffusive process with about 290 nm thickness. Material analysis allow us to describe the main mechanisms for oxynitride formation as well as correlate this phenomenology with some investigated plasma properties by OES analysis.
NSTL
Elsevier