Lordejani, Amir ArdeshiriVitali, LucaGuagliano, MarioBagherifard, Sara...
14页
查看更多>>摘要：The low working temperature of cold spray technology offers a unique possibility to deposit a wide variety of composite materials by mixing two or more constituent powders. However, while it is possible to precisely control the chemical composition of the mixture before spraying, the compositional yield in the deposit remains uncertain. This is mainly due the variation of deposition kinetics between the constituent phases leading to a compositional deviation with respect to the feedstock. The mismatch in thermo-mechanical properties of the materials included in the feedstock can also lead to the variation of deposit composition along its thickness. Here, we paired a probabilistic approach with finite element simulations to estimate the deposition efficiency of the mixed powder and assess the actual composition of the cold spray multi-material deposit. The developed model accounts for the interaction of the powders with the substrate and estimates the deposition probability based on the actual deformation of particles of each individual phase during deposition. The model is validated by comparison with experimental data in the case of zinc-aluminum mixture, that is known as a promising option for corrosion-resistant coatings thanks to its excellent cathodic protection. The results confirm the adeptness of the proposed model in predicting the deposition efficiency as well as deposit composition variation along the thickness with a high accuracy in the case of multi-material deposits.
查看更多>>摘要：Silver (Ag) and tantalum (Ta) ions were co-implanted into titanium nitride (TiN) films on medical titanium alloys (Ti-6Al-4V) to control the Ag/Ta ratios on the surfaces. Different ratios (e.g., Ag/Ta = 4:1, 2:1, and 1:1) were found to provide significant effects on the cytocompatibility and antibacterial properties of TiN films. The in vitro and in vivo results showed that the Ag/Ta-TiN samples with Ag+ and Ta+ co-implantation exhibited obvious inhibition of the release of toxic ions (e.g., V4+ and Al3+) from medical Ti-6Al-4V. An Ag/Ta ratio of 1:1 exhibited the highest corrosion resistance, best cell growth, outstanding antibacterial performance, and no in vivo toxicity. Ag/Ta(4:1)-TiN had the highest bacteriostatic rate of 95.7%. These results indicate that silver and tantalum co implantation can improve the cytocompatibility and antibacterial properties of titanium alloys, and an appropriate Ag/Ta ratio is the key factor in this regard.
Baigonakova, G. A.Marchenko, E. S.Yasenchuk, Yu F.Kokorev, O., V...
12页
查看更多>>摘要：In the study, gradient coatings with a nanometer thickness were successfully synthesized from Ti/Ni/Ti nano-laminates on the TiNi substrate in a nitrogen atmosphere at 900 degrees C. A technique for producing a gradient coating includes magnetron sputtering of Ti/Ni/Ti nanolayers with a total thickness of 75 nm and 150 nm on a TiNi substrate and further synthesis of the coating by annealing the sample in a nitrogen atmosphere. The developed technique allows to form stable phases of titanium nitride and intermetallic oxynitrides, which are a reliable barrier to nickel diffusion from the substrate to the surface. No nickel was found on the surface of the synthesized coatings. In the synthesized coating from 150 nm thick nanolaminate, these barriers are Ti4Ni2(N,O) and TiN phases. In the synthesized coating from 75 nm thick nanolaminate, these barriers are two continuous TiN layers. The cytocompatibility of the coating synthesized from Ti/Ni/Ti nanolaminates with a total thickness of 150 nm was positively affected by a mixed-phase composition of titanium nitrides and oxides, moderate roughness and hydrophilicity.
查看更多>>摘要：TiAlN-Ag composite coating was prepared by pulsed magnetron sputtering method on cemented carbide surface. The effect of silver content on the microstructure, mechanical properties and tribological behaviors of TiAlN-Ag composite coatings was studied. Results show that doping an appropriate amount of Ag into TiAlN coating can significantly refine the grain size of TiN nanocrystalline, reduce the internal stress, and improve hardness, plasticity and toughness, as well as the coating/substrate bond strength and tribological properties of the coating. Under dry friction conditions, the wear forms of TiAlN-Ag coating transfers from severe adhesion wear and brittle spalling of TiAlN coating to slight adhesion wear and abrasive wear, whereas the wear mechanism under oil lubrication changes from the comprehensive form of brittle fracture, fatigue peeling and abrasion to the mainly abrasive wear with slight fatigue spalling. Overall, the TiAlN-Ag composite coating with 2.40 at.% Ag exhibits the best comprehensive mechanical properties and wear resistance.
查看更多>>摘要：The diffusion of substrate material into absorbing layer and oxidation of metal substrate or cermet metal nanoparticles at high temperatures are known as inevitable problems of the solar selective absorbers. In this study, we consider the use of textured stainless steel (SS) surface coated with a protective AlCr oxide layer as a high temperature solar selective absorber. The textured SS surface was prepared by ion etching techniques and AlCr oxide protective layer was deposited by RF magnetron sputtering. The absorptivity and emissivity of the as-prepared absorbers were 0.86-0.92 and 0.151-0.168, respectively. In order to evaluate the thermal stability, the absorbers were annealed at 600-800 ? for different time in ambient atmosphere. Absorbers demonstrated a red shift of the onset of the reflectivity at all annealing temperatures. The high activation energy of 315 kJ/mol was calculated. In terms of thermal stability, the service lifetime of the absorbers at 500 ? was estimated to be about 100 years and at 700 and 800 ? the absorbers were stable at least 50 and 1 h, respectively. A detailed examination of the annealed absorber surface revealed growth of surface Mn3O4 nanocrystals, which resulted in observed change of the reflectance spectra, while the textured surface morphology had no significant change. The results show that the protective textured surface has much higher thermal stability in air than iron-based cermet absorbers.
Rosaz, GuillaumeBartkowska, AleksandraCarlos, Carlota P. A.Richard, Thibaut...
12页
查看更多>>摘要：The authors report in this paper the possibility to control the thickness profile of a thin film deposited by High Power Impulse Magnetron Sputtering (HiPIMS). It is shown that the combination between a HiPIMS discharge, an unbalanced magnetic configuration and the application of a negative bias onto the surface to coat enables tailoring on demand the coating thickness profile. This effect is hereafter used to coat complex shapes such as low-beta accelerating cavities with a niobium layer. The authors first present the magnetic design proposed to obtain an unbalanced cylindrical sputtering source. Numerical simulations are then used to predict the electron density and energy spatial distributions that can subsequently be correlated to the ionization region shape. Finally, the authors present the effect of such technique comparing Direct Current Magnetron Sputtering (DCMS), HiPIMS and biased HiPIMS using, respectively, a balanced and an unbalanced magnetic configuration, as well as detailing the effect of modifying either the magnetic field lines distribution or the magnetic strength.
查看更多>>摘要：PPS/PTFE-bronze coatings were prepared by electrohydrodynamic jet deposition on the surface of AISI 1045 steel to improve the tribological property and corrosion resistance of the steel. Three different thicknesses of PPS/PTFE-bronze coatings were prepared to investigate the effect of coating thickness on the coating properties. The surface morphology and surface contact angle of the coatings were measured, and the looseness of the coatings was evaluated using scratch tests. The tribological property and corrosion resistance of PPS/PTFE-bronze coatings with different thicknesses were tested by reciprocating sliding dry friction experiment and electrochemical workstation, respectively. The results showed that the wear rate of the coating filled with irregular tin bronze particles at the thickness of 24 layers was 6.5 times higher than that at the thickness of 12 layers, and the corrosion current density was also doubled. This was because the number of irregular bronze particles increased as the coating thickened, making the cross-linking reaction more obstructed. As a result, the cross-linking density decreased and the coating structure became looser, leading to the decreases in the tribo-logical property and corrosion resistance of the PPS/PTFE-bronze coatings with thickness.
Munoz-Pina, S.Alcaide, A. M.Limones-Ahijon, B.Oliva-Ramirez, M....
12页
查看更多>>摘要：It is demonstrated that, besides classical nanocolumnar arrays, the oblique angle geometry induces the growth of singular structures in the nanoscale when using wisely designed patterned substrates. Well-ordered array of crosses, cylindrical nanorods or hole structures arranged in square or hexagonal regular geometries are reported as examples, among others. The fundamental framework connecting substrate topography and film growth at oblique angles is presented, allowing the use of substrate patterning as a feasible thin film nanostructuring technique. A systematic analysis of the growth of TiO2 thin films on 4 different lithographic patterned substrates in 4 different scale lengths is also presented. A first conclusion is the existence of a height-based selective growth in the initial stages of the deposition, by which the film preferentially develops on top of the tallest substrate features. This behavior is maintained until the film reaches a critical thickness, the so-called Oblivion Thickness, above which the film topography becomes gradually independent of the substrate features. A general formula relating the spatial features of the pattern, the coarsening exponent and the Oblivion Thickness has been deduced.
查看更多>>摘要：In this study, an Mg-Y-Nd-Gd-Zr alloy was subjected to ultrasonic surface rolling processing (USRP), and a deformation layer approximately 651 mu m deep was observed. It shows a double-gradient microstructure as the grain size increased and the twin density decreased. The grain size at the top surface layer was refined to 147.08 nm, and several stacking faults (SFs) were observed in the nanograins. Two main types of SFs were observed, including intrinsic I-1 SFs bounded by 1/6<20(2)over bar3> Frank partial dislocations and intrinsic I-2 SFs bounded by 1/3<10(1)over bar0> Shockley partial dislocations. The SFs induced a strong hindrance to dislocation motion, improving the yield strength of the alloy. Also, the dislocation caused by SFs increased the stress concentration of the nanograins and promoted premature fracture failure at the top surface of the alloy, reducing its plasticity after USRP. In addition, the tensile fracture of the alloy changed from plastic fracture mechanism dominated by micropore aggregation before USRP to brittle fracture mechanism dominated by cleavage planes and steps after USRP.
查看更多>>摘要：In this paper, an iterative approach combined with least squares fitting of limited measured points is introduced to reconstruct residual stress distribution after laser shock peening (LSP) treatment. The iterative approach is started by introducing prescribed stress components in the data measurement region (the mapped zone) in the finite element (FE) model, then a static equilibrium analysis is conducted, which will cause the stress distribution in the mapped zone and unmapped zone both redistribute if they don't converge to the target stresses. By repeatedly introducing the input stress in the mapped zone to converge to the prescribed stress components, the complete residual stress distribution in the whole region can be obtained. Firstly, to validate the viability of this method, based on the full stress components information of 'measured' sample points extracted from FE models, residual stress reconstructions of single-pass welding of a thick plate and a single shot of LSP have been carried out, respectively. After that, to examine the robustness of the method, the iterative approach combined with multi-dimensional least squares fitting is tested using a limited set of 'measured' sample points extracted from the FE model of single shot LSP treatment. It is found that besides the commonly studied depth direction, the in-plane stress components are also varied with its in-plane locations, which are due to "edge effects". The residual stress fields for the whole region reconstructed by the proposed approach agree well with the actual stress fields even if some of the non-critical stress information are missing. Finally, the results are compared with those reconstructed by the eigenstrain method. It is shown that the proposed iteration approach can reconstruct the residual stress distribution in the whole region at a satisfactory level by solving a direct linear elastic static equilibrium problem, while the eigenstrain method needs to solve an inverse problem to obtain the appropriate eigenstrain distribution.
NSTL
Elsevier