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：Complex geometries can be produced by laser powder bed fusion (LPBF) techniques in a layer-by-layer manner. These parts exhibit inhomogeneous microstructure and poor surface quality in their as-built state. Performing post-treatments to modify these imperfections can play a substantial role in enhancing the performance of LPBF parts. However, the effects of post treatments on local geometrical irregularities are not still well documented. In this study, four different post-treatments including heat treatment, mechanical and chemical surface treatments as well as their combination were considered. Their effect was studied on microstructure, surface, and mechanical properties of LPBF V-notched AlSi10Mg samples. The as-built samples were subjected to two different shot peening processes (using different Almen intensity, shot diameter, and shot hardness), chemical polishing and electro-chemical polishing, in individual and combined configurations. Comprehensive microstructural characterization was carried out and the surface state of the samples was studied in detail in terms of surface morphology and roughness. In addition, mechanical properties including microhardness and residual stresses were measured and finally the fatigue behaviors of the samples were analyzed and compared at a constant stress level. All post treatments led to improved fatigue life. The combination of the aforementioned post-treatments led to a remarkable fatigue life improvement up to 414 times higher compared to the as-built state.
Denissen, Paul J.Homborg, Axel M.Garcia, Santiago J.
12页
查看更多>>摘要：In this work a diffusion-driven inhibitor transport model is used to help in the design of inhibitor-loaded carriers for anticorrosive primers. The work focuses on inhibitor release at damaged locations of different dimensions exposed to electrolyte and is validated experimentally. The damage dimensions are first simulated to determine the minimal inhibitor release rate necessary to reach the required inhibitor concentrations for corrosion protection of the exposed metal. Kinematic and mass conservation laws are then used as first-order approximations to study the effect of different characteristics of nano-and micro-particles loaded with inhibitors embedded in an organic coating during the first 100 s of immersion. The simulated results are validated experimentally using epoxy coatings containing cerium-loaded zeolites and diatomaceous earth as nano-and micro-carriers respectively. These experiments confirmed the simulated predictions, showing that under the used exposure conditions nano-particles are only able to protect relatively small damages of micron size dimensions. Micron-sized carriers on the other hand allow sufficient release to protect larger damages, even at lower pigment volume concentrations. Additional simulations on rapid electrolyte diffusion pathways inside the coating are also in good agreement with the experiments, indicating the presence of diffusion pathways might play an important role in sustained inhibitor release and corrosion protection at local damages.
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.
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.
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.
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：Due to well-balanced mechanical properties and density ratio, gamma-TiAl alloys have been extensively investigated for potential aircraft jet engine applications. However, their use is restricted by limited oxidation resistance at temperatures above 750 degrees C. The present study focuses on the development of titanium silicide protective coatings using different Si reservoirs (3.0 mu m, 6.0 mu m and 9.5 mu m of initial Si thickness) deposited by magnetron sputtering, followed by different periods (2 h to 24 h) of vacuum thermal annealing at 950 degrees C. The growth of titanium silicides and evolution of the composition and microstructure following oxidation was investigated using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD) techniques. The initial Si thickness and annealing time have an influence on the formation of different zones of composition, assigned as the TixSiy layer, interdiffusion zone and TiAl2 zone, which are correlated with their oxidation behavior at 900 degrees C in laboratory air after 100 h. The gamma-TiAl substrates with Si-based coatings presented a protective inner layer of TixSiy. The coatings with initial 3 mu m of Si show formation of mixed Si and Ti oxides as well as minor Al content, and traces of Cr at the oxide scale. The oxidation process is described by the parabolic oxidation coefficient, k(p), with values of k(p) = 3.5-8.9 x 10(-12) g(2).cm(-4).s(-1) for the coated surfaces, one order of magnitude lower than for the bare substrate. In comparison, the coating systems possessing a higher initial Si thickness (6.0 mu m and 9.5 mu m) mainly exhibit the mixed formation of dense Si and Al oxide scales with significant Cr enrichment.
查看更多>>摘要：Versatile surfaces with hydrophobicity gradients have attracted intensive attention because of their tunable wettability. Here, cerium oxide films are prepared on tilted substrates by magnetron sputtering, the induced thickness gradient strongly influences the structural, morphological and wetting properties. It is found that the surface hydrophobicity is positively proportional to the root-mean-square (RMS) roughness and thickness variations, larger thickness gradient brings more obvious gradient hydrophobic surfaces. The results show that the RMS roughness gradient increases from 0 nm/cm, 0.08 nm/cm to 0.16 nm/cm and the thickness gradient increases from 0 nm/cm, 12.0 nm/cm to 13.2 nm/cm, with the tilt angle changing from 0 degrees, 30 degrees to 60 degrees, respectively. Correspondingly, the hydrophobicity gradient increases from 0 degrees/cm, 1.6 degrees/cm to 2.7 degrees/cm, respectively. Our study offers practicable method a method for developing hydrophobicity gradient surfaces, which can be used for droplet movement applications.
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.
NSTL
Elsevier