Kancharla, HarikrishnaMandal, G. K.Singh, S. S.Mondal, K....
14页
查看更多>>摘要：The present work investigates the effect of three different strip entry temperatures (SETs) (500, 575, and 650 ?) on the extremely thin aluminum (Al)-rich inhibition layer formed at the substrate-coating interface during galvanization in a Zn-0.2 wt% Al bath and its correlation with the corrosion behavior in freely aerated 3.5 wt% NaCl solution. The scanning electron microscopy confirms that the morphology of the interfacial layer becomes coarser with an increase in SET. Moreover, the rate of Al uptake at the interfacial layer increases with increasing the SET due to an increase in the effective reaction temperature for the nucleation of Fe-Al crystals at the substrate liquid zinc interface. X-ray diffraction also reveals that the texture coefficient (TC) of the preferred high atomically dense (0002) basal plane of Zn coating is pronounced at lower SETs. It has been found that the coating prepared at 500 degrees C has the lowest corrosion rate of 0.142 mm/y as compared to that prepared at 575 degrees C (0.245 mm/y) and 650 degrees C (0.266 mm/y). Electrochemical impedance spectroscopy also follows a similar trend. It has been observed that the dominance of the highest packing density (0002) crystal plane, compact interfacial layer as well as uniform and compact pore-free coating surface have resulted in the lowest corrosion rate of the coating made at the lowest SET of 500 degrees C.
查看更多>>摘要：Thermal spray technologies continuously evolve to meet new challenges arising from current and future market needs and requirements. This evolution has been well documented throughout the years with regards to equipment, processes and materials but the concurrent digital transformation of the sector is happening in a fragmented manner. The first objective of this article is to review the readily available digital tools and methods for coating deposition optimisation, equipment health monitoring, process control and metallographic analysis. The second objective is to identify the key challenges faced by industrialists and to provide some guidance and recommendations for the research and development required to meet these challenges. The third objective is to assess the performance of the most promising Machine Learning (ML) methods, as a key enabling technology, for thermal and cold spray. Novel approaches from different engineering disciplines, currently unexplored in the field of surface engineering, are discussed and several adoption strategies are proposed. Machine learning validation examples with their implementation codes are presented in this work in an effort to motivate new research that would eventually accelerate the digital transformation of the surface engineering sector.
查看更多>>摘要：The crystallographic microstructure between the electroplated Cu fillings and the substrate in a stacked-via structure and its electrical/mechanical characteristics were systematically investigated using a focused ion beam (FIB), electron backscatter diffraction (EBSD), a probe station with an ohmmeter, a quick via pull (QVP) test, and a 3D-optical microscope. A two-stage Cu electrodeposition process with various plating current densities at the early stage (j(1) = 0.3, 0.5, 1.0, or 2.0 A/dm(2)) and a fixed plating current density at the subsequent stage (j(2) = 2.0 A/dm(2)) was utilized to fill a daisy-chain blind-hole (BH) structure. The Cu crystal coherency between electroplated Cu fillings and substrate can be significantly improved with the j(1) minimization, which efficiently enhances the electrical/mechanical characteristics of the stacked-via structure. The strong dependence of the Cu crystal coherency on j(1) can be ascribed to a slow discharge rate of Cu ions at a low plating current density, allowing the Cu nuclei to laterally extend and epitaxially grow with a crystalline substrate. Therefore, the Cu crystal modification via j(1) adjustment can greatly promote the packaging reliabilities of a stacked-via structure.
查看更多>>摘要：The main purpose of this article is to study the effect of ultrasonic surface rolling process (USRP) on the surface properties of QAl10-3-1.5 aluminum bronze alloy under different rolling reduction and rolling times, providing ideas for improving the poor wear resistance of valve stem nuts and sealing rings. SEM, EDS and optical threedimensional profiler were used to characterize the microstructure characteristics of the surface modified layer and the surface morphology of the wear traces. The results show that the surface layer of the USRPed sample has undergone severe plastic deformation. The alpha phase is elongated, and the microstructure structure shows a fine and uniform distribution state. And the grain size of alpha phases decreased, and the number density of beta phases increased. Compared with the untreated sample (only cutting and polishing), the surface roughness of the USRPed sample reaches nearly Ra 0.04 mu m; the maximum surface micro-hardness is 323.04 HV, increasing by 75%; the maximum depth of surface hardening layer is about 570 mu m. The friction coefficient, wear mass loss and the width and depth of the wear traces of the USRPed samples are significantly reduced, while the wear resistance is significantly enhanced. By comparing the surface wear morphology of the samples under different process parameters, it is found that the main wear mechanism of the untreated samples is adhesive wear, while the main wear mechanism of the USRPed samples is abrasive wear. The improvement in wear resistance is attributed to the refined and homogenized surface microstructure, the smaller surface roughness, the larger surface micro-hardness and surface hardness layer depth after USRP.
查看更多>>摘要：The design of multilayered structure is a promising way to tailor the microstructure and properties of the hard coatings. In this study, AlCrN, AlTiSiN and nano-multilayer AlCrN/AlTiSiN coatings were deposited and their microstructure, mechanical, oxidation and cutting properties were comparatively investigated. The results showed that the AlCrN/AlTiSiN coating, possessing two phase and denser microstructure, showed improved hardness (39.4 GPa) and adhesion strength, as compared with the AlCrN and AlTiSiN coatings. The AlCrN/ AlTiSiN coating also exhibited excellent oxidation resistance up to 1000 C and its oxidation scale was composed of a thin and dense Al-rich oxide, due to the multilayer structure acted as an effective barrier to block elemental diffusion to retard the oxidation process. In the turning tests for SKD11, the AlCrN/AlTiSiN coating demonstrated good tool life (-800 m), which should be attributed to its higher hardness, good adhesion strength and oxidation resistance, as compared with the monolithic AlCrN and AlTiSiN coatings.
查看更多>>摘要：In the present study, an Al2O3 ceramic coating was formed on a pure titanium surface with the application of the duplex coating technology produced by combining hot-dip aluminizing (HDA) and micro-arc oxidation (MAO) processes. Due to the porous nature of MAO coating with the structural and mechanical differences between the MAO (Al2O3) and HDA layers (Al, Al3Ti), diffusion annealing treatment was applied to duplex coated (HDA + MAO) titanium samples. With the diffusion annealing treatment, a composite layer with a thickness of about 125 mu m was formed beneath the modified MAO coating, which showed a denser structure by penetrating TiO2 into the MAO. MAO coatings with and without diffusion annealing exhibited compressive residual stresses with values of-1530 and-850 MPa, respectively. Microhardness and elastic modulus of the diffusion annealing-treated MAO coating reached 1230.1 HV and 241.3 GPa, respectively. The diffusion annealing-treated MAO coating provided-29% less coefficient of friction and-8.4 times greater relative wear resistance than that of MAO coating without diffusion annealing.
查看更多>>摘要：High-performance precision gear drives such as harmonic gear have high requirements on tooth profile accuracy, surface quality, fatigue life and other service performance characteristics, which urgently needs an effective surface strengthening method. This work aims to examine the feasibility and effectiveness of fine particle peening (FPP) treatment on surface integrity of flexspline in harmonic drive precision transmission. To this end, FPP process experiments were carried out, and this process was simulated based on a coupling method of discrete element method and finite element method (DEM-FEM) considering the kinematic hardening behavior of the material. The simulation results were in good agreement with the test results. Effects of shot peening pressure, injection velocity, material properties and tooth profile on surface roughness and induced residual stress of the target flexspline were analyzed. The results reveal that after FPP, the amplitude of residual compressive stress of the flexspline can reach 470 MPa, and the surface roughness Sa becomes approximately 0.5 mu m. For precision gears with low hardness such as flexspline in harmonic drive, it is suggested to adopt FPP with low air pressure to achieve both saturated residual compressive stress and lower surface roughness, thus benefitting enhanced fa-tigue life.
查看更多>>摘要：In this study, multilayered AlTiN/ZrN and AlTiN/CrN/ZrN coatings with CrN layer addition were prepared by cathodic arc evaporation (CAE) system using AlTi target, Cr target and Zr targets. According to the XRD and TEM experimental results, the coatings are all B1 NaCl structure, and the columnar structure continues from the bottom CrN to the top multilayered coating and the growth of the columns is not interrupted. After CrN addition, the AlTiN/CrN/ZrN coating consisted of ZrN, AlTiN and CrN multilayers. By increasing the cathode current of Cr, thicker CrN layers were obtained. The nanoindentation results showed that the AlTiZrN had the highest hardness of 30.4 GPa and residual stress of -3.1 GPa, mainly due to the contribution of ZrN into AlTiN. The multilayered Al12Ti7Cr12Zr22N and Al8Ti5Cr21Zr17N coatings with different CrN layer thicknesses had lower hardness values. Compared to the low hardness of CrN (~18 GPa), the multilayered AlTiN/CrN/ZrN coating still possessed high hardness enough. In addition, after CrN addition, the multilayered Al12Ti7Cr12Zr22N and Al8Ti5Cr21Zr17N coatings had lower residual stresses (-1.6-2.6 GPa). The low residual stress of the hard coating is beneficial for tribological applications. For the ball-on-disc tribological tests, although the AlTiN/ZrN coating had the highest hardness but it had the highest wear rate (4.96 x 10(-6) mm(3)/Nm). The multilayered Al12Ti7Cr12Zr22N coatings with thin CrN layer addition and small Cr content had the best wear performance with the lowest wear rate of 4.21 x 10(-7) mm(3)/Nm. The results showed that the special multilayered AlTiN/CrN/ZrN hard coating possessed better wear performance than that of AlTiN/ZrN coating, which was due to the fact that the multilayer architecture with CrN addition effectively released the internal stress to resist abrasion wear.
Berekchiian, M. V.Simonenko, N. P.Lyskov, N. V.Napolskii, K. S....
7页
查看更多>>摘要：Selenic acid electrolyte provides porous anodic aluminium oxide (AAO) films with low porosity and high optical transparency. Here, the high-temperature behaviour of AAO obtained in a selenic acid electrolyte is reported for the first time. The crystallization of as-prepared amorphous AAO at about 800 degrees C is accompanied by the elimination of electrolyte impurities, an increase in pore diameter from 15 to 21 nm, and an increase in specific surface area to 55 m(2).g(-1) due to the mesopore formation inside the cell walls. The second crystallization stage at about 1150 degrees C results in the formation of coarse-grained corundum (alpha-Al2O3) films with a mean grain size of about 11 mu m. Each of the grains consists of regularly arranged 27-nm-diameter pores, which are stable up to 1300 degrees C. AAO physicochemical properties depend on the annealing temperature. In particular, chemical stability is up to three orders of magnitude higher after two-step crystallization. Optical properties and thermal expansion of selenic-acid-made porous AAO films with different phase composition are quantified. The crystallization of as prepared AAO to low-temperature Al2O3 polymorphs has a minor influence on optical transmittance and effective refractive index of AAO, whereas the coarse-grained structure of corundum causes an order of magnitude decrease in average transmittance in the visible region. The coefficient of thermal expansion increases by 25% to 8.5 x 10(-6) K-1 for alpha-Al2O3 porous films compared to as-prepared AAO.
de la Hoz, Maria Florencia TanoSanchez, Andrea GomezMariscotti, ValentinaProcaccini, Raul...
8页
查看更多>>摘要：The effect of functionalization of anodized zirconium (Zr) with RGD peptides on cell behavior as a feasible approach to stimulate early bone integration is presented. The surface modifications were evaluated by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Electrochemical tests were performed to determine the effect of functionalization on the stability of the anodized zirconium oxide film. Finally, the biocompatibility of the material was evaluated in an in vitro cell model. Surface analysis showed the presence of peptides on the surface after functionalization, and that the crystal structure of the oxide formed by anodization is predominantly monoclinic. The immobilization of RGD peptides on anodized Zr does not alter the corrosion protection provided by the anodic oxide and significantly promote cell adhesion and spreading in vitro. Thus, the combination of RGD peptides with anodic oxide on Zr surface would represent a useful strategy to increases the biocompatibility of the material.
NSTL
Elsevier