Moreno-Murguia, B.Mora-Garcia, A. G.Canales-Siller, H.Giraldo-Betancur, A. L....
8页
查看更多>>摘要：The effect of particle velocity on deposition efficiency and microstructure of copper powder on aluminum alloy substrates using Low Pressure Cold Spray (LPCS) is here reported. For this, experimental substrate-coating systems were fabricated varying powder feed rate, transverse speed, and air pressure keeping the compressed air, substrate temperature, and stand-off distance constant (600 degrees C, 100 degrees C, and 5 mm, respectively). From the combination of low feed rates and low transverse speed, deposition efficiency tends to increase. The maximum deposition efficiency of 34.8% was obtained for a feed rate of 0.2 g/s, 10 mm/s transverse speed, and 8 bar of air pressure. The pressure and stand-off distance effect on coatings was studied measuring the particle velocity with and without substrate. For this, spraying conditions were varied between 5-8 bar and 5-15 mm, respectively. Experimental measurements were compared with results from computational fluid dynamics simulation to understand the effect of the spraying parameters on the complete powder size distribution. The highest deposition efficiencies (36-37.5%) were obtained at 7 bar air pressure for spray distances between 5 and 12.5 mm. Increasing the pressure to 8 bar led to a decrease in the deposition efficiency (6-11%). The tendency of deposition efficiency seems to match with the in-flight particle velocity influenced by the presence of a substrate, which serves as evidence of the bounce-off effect. The reduction of the particle velocity, along with the low transverse speed seems to remove less attached particles by erosion through the peening effect.
查看更多>>摘要：ABSTR A C T The finite element (FE) model is established based on the microstructure of the double-ceramic-layer thermal barrier coating system (DCL-TBCs). Different structural parameters are sampled by Latin hypercube Sampling method to construct corresponding models. The energy release rates of the interfacial crack, which is between lanthanum zirconate (LZ) layer and yttria-partially stabilized zirconia (YSZ) layer of DCL-TBCs, are calculated by numerical simulation during cooling and a dataset is created according to the results. On the basis of the dataset, a surrogate model is constructed to predict the maximum energy release rate during cooling by the extreme random forest algorithm, and the prediction accuracy of the surrogate model is verified by testing dataset. The thicknesses and porosities of the LZ and YSZ layers of DCL-TBCs, and the length of the interfacial crack are set as input variables, and the maximum energy release rate during cooling process is set as output variables of the surrogate model. Using the surrogate model and the particle swarm optimization (PSO) method, the LZ and YSZ layers with different combination of thicknesses is optimized to minimize the energy release rate of the inter-facial crack of DCL-TBCs.
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：Residual stresses have significant influences on the in-service performance of materials. Laser shock peening (LSP), a technique generating processing-based residual stress, is employed to introduce high-amplitude and large-depth compressive residual stress in SiC particle-reinforced 2009 aluminum (SiC/2009Al) metal matrix composites. Surface residual stresses after single-shot LSP and multiple shots of overlapped LSP were investigated. Single-shot LSP with 10 J, 20 J, 30 J, and 40 J laser energies introduced average surface residual stresses of-126.7 MPa,-129.3 MPa,-85.7 MPa, and-69.3 MPa. Multiple shots with energies of 20 J were inflicted twice on the surface undergoing LSP and exhibited a maximum residual compressive stress of-266.7 MPa. Then, the surface residual stress decreased from-266.7 MPa to-215.3 MPa and further to-212.7 MPa when subjected to 10,000 and 100,000 fatigue cycles. Relaxation also occurred under thermal loads, and the stress decreased from-266.7 MPa to-129.3 MPa after holding at 100 & DEG;C for 50 h. Furthermore, simulation of the LSP process was conducted with the SiC/2009Al composite and showed that SiC particles close to the peening surface generated more reverse plastic deformation and resulted in some residual tensile stress in their surroundings. This combined experimental and numerical research seeks to provide deep insight into residual stress distribution and explore the applicability of LSP with metal matrix composites.
查看更多>>摘要：A double rare-earth (Yb/Y) co-doped SrZrO3 [Sr-1.0(Zr0.9Yb0.05Y0.05)O-2.95] thermal barrier coating was prepared via suspension plasma spraying (SPS). The rare-earth nitrates [Zr(NO3)4 center dot 5H(2)O, Sr(NO3)(2), Yb(NO3)(3)center dot 6H(2)O, Y (NO3)(3)center dot 6H(2)O] and NH4(C2O4)(2)center dot H2O were used to prepare the precursor suspension by co-precipitation. The thermal decomposition and crystallization of the precursor suspension powders calcined at 1200 degrees C were characterized with X-ray diffraction and a synchronous thermal analyzer coupled with quadrupole mass spec-trometry. Zr-2(C2O4)(2)(OH)(4) decomposed into Zr(C2O4)(2), ZrO2, and H2O initially, followed by the decomposition of Zr(CO3)(2) into ZrO2. The SrC2O4 precursor decomposed into SrCO3 and SrO consecutively. The ZrO2 reacted with SrO (Yb2O3, Y2O3) to generate the Yb/Y co-doped SrZrO3. And the Yb/Y co-doped SrZrO3 coating with a columnar crystal structure was prepared by SPS, which was analyzed with scanning electron microscopy, an inductively coupled plasma atomic emission spectrometer, and a laser flash analyzer. The thermal conductivity of the as-prepared coating was 1.77 W.m- 1.K-1 at 1000 ?C, which was more than 19% lower than that of the SPS SrZrO3 coating.
Kim, Min-YoungPark, Sang-JunKang, Byeong-SuLim, Jinsub...
9页
查看更多>>摘要：In order to improve the charge/discharge cycle characteristics of the all-solid lithium batteries (ASLBs) operated at high temperature (60-80 ?), the TiO2-coated NCM-424 (LiNi0.4Co0.2Mn0.2O2) by the sol-gel method was investigated. Two kinds of key parameter, coating amount of TiO2 on NCM-424 powder and calcination temperature, were controlled for synthesis of TiO2-coated NCM-424. Firstly, to investigate the effect of coating amount, NCM-424 powders were coated with 1-5 wt% TiO2 and calcined at 600 ?. Secondly, the calcination temperature was changed in the range of 525-800 ? on the precursor of 3 wt% TiO2-coated NCM-424. In the case of the former sample, it seems that although the number of fine TiO2 grains on the surface of NCM-424 particle was increased with increasing of coating amount, the main factors constituting the material, ie, lattice parameters are almost unchanged on all samples. For about 30 cycle on coin cells of a composite type ASLBs, the 3 wt%-coated sample calcined 600 ? showed the best discharge capacity (about 136 mAh g(-1) at 70 ?) and good cycle behavior among the samples. In the latter case, it was found that when the calcination temperature was increased to 800 ?, side-reaction between TiO2 and NCM-424 powder was occurred to form a new interface, which had a good effect on cycling property of ASLB cell. That is, the initial capacity of cell with 3 wt% TiO2-coated NCM-424 was decreased slightly, but the capacity retention behavior with charge/discharge cycle was greatly improved when the calcination temperature was increased from 600 ? to 800 ?; the initial capacity of 3 wt% TiO2-coated NCM-424 calcined at 800 ? was about 127 mAh g(-1) at 70 ?, and its capacity retention was about 81% at 100 cycle. On the other hand, the capacity retention of TiO2-coated NCM-424 materials calcined at 600 ? or less tend to decrease rapidly after 50 cycles. These results are presumed to be related to the structural change of TiO2, NCM-424 materials itself, and the difference of coating adhesion according to the calcination temperature.
查看更多>>摘要：Plasma electrolytic oxidation (PEO) is a cost-effective and versatile technique to achieve protective oxide coatings in light metals. Composite coatings containing B4C nanoparticles were produced by the PEO technique on a Ti6Al4V alloy. The influence of nanoparticles on the microstructure and corrosion resistance of the prepared ceramic composite coatings, as well as its incorporation mechanism into the PEO layer, were investigated. B4C nanoparticles were added to aluminate-based electrolytes and a pulse power supply was used as a constant voltage regime to obtain PEO composite coatings. Improvement in corrosion protection was also assessed by electrochemical impedance spectroscopy (EIS) and polarization tests, illustrating that a reduction in the corrosion resistance ratio was 8 for the composite coating compared to 16 for the sample without nanoparticles, after three weeks of immersion. The effect of nanoparticles on the phase composition was examined by X-ray diffraction (XRD) tests. Moreover, scanning electron microscopy (SEM) images illustrated the capability of B4C nanoparticles in filling the inherent pores of PEO coatings.
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.
NSTL
Elsevier