Surface Review and Letters

The present study investigates the superelasticity properties of spark plasma sintered (SPS) nickel titanium shape memory alloy (NiTi SMA) with the influence of sintering temperature and particle size. The nanoindentation is conducted on the surface of the NiTi SMA at various loads such as 100, 300 and 500mN. The nanoindentation technique determines the quantitative results of elasto-plastic properties such as depth recovery in the form of superelasticity, stiffness, hardness and work recovery ratio from load–depth ($P$–$h$) data during loading and unloading of the indenter. Experimental findings show that the depth and work recovery ratio increases with the decrease of indentation load and particle size. In contrast, increasing the sintering temperature exhibited a better depth and work recovery due to the removal of pores which could enhance the reverse transformation. The contact stiffness is influenced by $dp∕dh$ which leads to attain a maximum stiffness at the highest load (500mN) and particle size (45$\mu$m) along with the lowest sintering temperature (700^∘C). NiTi alloy exhibited a maximum hardness of 9.46GPa when subjected to indent at the lowest load and particle size sintered at 800^∘C. The present study reveals a better superelastic behavior in NiTi SMA by reducing the particle size and indentation load associated with the enhancement of sintering temperature.

The three-dimensional semi-infinite mixed spin-1/2 and spin-3/2 ferrimagnetic Ising system with crystal field is investigated using the mean-field approximation and the Monte Carlo simulation. According to the ratio $R$ of bulk and surface exchange interactions and the ratio $Y$ of bulk and surface crystal fields, we have classified four qualitative types of phase diagrams characterized by the presence or absence of ordinary, extraordinary, surface and special phase transitions. The critical behavior of the surface and bulk magnetizations has also been highlighted in the vicinity of these different transitions. At low temperatures, two critical end-points appear in the bulk and on the surface in the ordered region limiting two successive first-order phase transitions. Furthermore, we have made a comparison with other works on similar models in pure or mixed versions.

An aluminized coating for low-carbon steel with good corrosion and wear resistance was first prepared through low-temperature pack aluminization. Then, the low-temperature-aluminized steel substrate was subjected to thermal oxidation in air. The phase composition, surface morphology, roughness, and elemental distribution of the aluminized carbon steel both before and after thermal oxidation were analyzed through X-ray diffraction spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The corrosion resistance and wear resistance of the original carbon steel substrate, aluminized carbon steel, and oxidized carbon steel were tested. Results showed that nanowires composed of iron oxide and alumina formed in situ on the top layer of the aluminized carbon steel. The corrosion resistance and wear resistance of the low-carbon steel with the nanowire oxide coating were better than those of the original carbon steel and aluminized carbon steel because the in-situ nanowire oxide film improved the density of the aluminized coating.

In the present study, a scalable-manufactured and environmental-friendly method was proposed to fabricate the superhydrophobic coating on titanium alloy. The hierarchical binary surface structures were obtained by hydrothermal treatment of titanium alloy with oxalic acid and sodium hydroxide solutions successively. The hierarchical structure surfaces after fluoroalkyl-silane modification possessed a maximum contact angle of 158.7^∘ and a sliding angle of 4.3^∘. The low contact angle hysteresis surface can lead to efficient self-cleaning performance, which was confirmed by the bounce and roll off of water droplet on the surface. Furthermore, the anticorrosion behaviors of the superhydrophobic coating in 3.5wt.% NaCl solution was evaluated by the electrochemical impedance spectroscopy (EIS). It was found that the superhydrophobic coating can maintain its superhydrophobic state (150^∘) within 48 h, thereby effectively preventing the corrosive medium from penetrating into the coating. This simple yet fast anti-corrosion/self-cleaning superhydrophobic coating manufacturing strategy will enlighten its potential application in the engineering fields.

Gold nanorod ribbon-like arrays as well as shape-separation effect of rods from sphere-like nanoparticles have been evaluated for identical nanorod suspension with various concentration of nanospheres. These sphere-rod mixtures are prepared with help of different amounts of AgNO₃. Deposits of nanoparticles at various positions of the coffee-stain ring are observed in different arrangements. For instance, face-to-face aligned nanorods get settled in ribbon-like superstructures and these arrays are observed to be self-separated from spheres. Self-assembly and shape-separation effect are observed more systematic at the outer-edges than the inner-region of the coffee-stain ring. Experimentally, it has been observed that face-to-face formation of nanorods in suspension is energetically more probable arrangement. As the separation between two nanorods increases, the depth of potential well decreases, indicating that the upper layers of nanorods are more under the influence of lower placed nanorods than those placed in the same plane. Energetically and sterically, more feasible arrangements are observed.

Laser shock peening (LSP) was employed to squeeze compressive residual stress (CRS) into the curved surface of the round rod with diameter of 16mm. The residual stress field was induced by nine laser shots irradiating at different locations along the specified path. The developing process of the residual stress field was investigated with finite element analysis, and the corresponding experiments were also carried out to validate the calculated results. Results demonstrate that multiple LSP with 50% overlapping rate can result in residual stress field with the maximum CRS varying from 155.2MPa to 198.8MPa along the direction of the rod axis. The peened surface appears wavy in shape and the maximum depth of plastic deformation in the curved surface is 13.41$\mu$m. The value of surface roughness increases from 3.87$\mu$m to 4.65$\mu$m.

In this paper, titanium dioxide methylene blue molecularly imprinted polymer (TiO₂-MB-MIP) was prepared by using MB-MIP as supported carrier. Through the study of its adsorption performance and photodegradability, it was found that the prepared TiO₂-MB-MIP has both the adsorption capacity and the photodegradation capacity on MB. The static adsorption experiment shows that its adsorption and photodegradation capacity can reach 1202.1mg⋅g${}^{-1}$ when the original concentration of MB is 5.0mg⋅mL${}^{-1}$. In addition, the degradation ability of the material in MB aqueous solutions was studied under varying light conditions. By analyzing the nitrogen and carbon content in the adsorbed solutions, the degradation process was found that the carbon and heteroatoms nitrogen in MB can be degraded to CO₂, and NH${}_4^{+}$ or NO${}_3^{-}$, respectively. The adsorption isotherm thermodynamics and kinetics model study found that the adsorption process conforms to the Langmuir isotherm equation and the quasi-secondary kinetic model, indicating that the adsorption is basically monolayer adsorption and the adsorption process is the chemical rate control step. The TiO₂-MB-MIP can be used to protect our environment by treating pigment wastewater efficiently.

Today, conventional machining with chip or machining without chip machining manufacturing methods is used to bring to the desired dimensions sizes the machines and equipment used in the industry. However, non-traditional manufacturing methods are used in cases where traditional machining manufacturing methods are inadequate. Cutting with water jet which is one of the non-traditional manufacturing methods is commonly used in several fields of industry. Unlike traditional manufacturing methods such as turning and milling, not using of a physical cutting tool is among the advantages of the method. Abrasive water jet manufacturing method was started to be applied by adding abrasive particles in the water jet. Apart from the superior properties of the method, possible damages occur in the water jet nozzle due to processes such as cutting or drilling by applying high pressure. Erosion-corrosion is the leading damage among these damages. In this study, the erosion-corrosion in the nozzle caused by high-pressure water and abrasive during the abrasive water jet cutting process was simulated in the computer environment. In this paper, the erosion rate in the nozzle was calculated as 6,90E-06kg/m²s. This value was converted as 0,30mm (27,09mm for yearly) via developed software for 100h.

Effects of different pulse widths on morphologies and corrosion resistance of diamond-like carbon (DLC) coatings prepared on the surface of high nitrogen nickel-free stainless steel (HNSS) were investigated. It was found that different pulse widths of 10, 15 and 20$\mu$s mainly affect the porosity and internal stress within the coatings. The energies of the implantation ions were decreased as the pulse width increase. The growth mechanism of the coating with the pulse width of 20$\mu$s was mainly surface diffusion, in which the coating was porous and prone to corrosion. With the decrease of pulse width, the growth mechanism was mainly sub-plantation. The DLC coating became dense and the corrosion resistance was improved significantly. However, with further decrease of pulse width, internal stress within the coating was also increased. The effect of stress corrosion cracking may decrease the corrosion resistance of the DLC coating with the pulse width of 10$\mu$s. The influencing mechanisms of the pulse width on corrosion resistance and growth mechanism of DLC coating on the surface of HNSS are also discussed.

A silica-based organic–inorganic hybrid coating has been developed for corrosion protection of aluminum substrates by dip-coating technique. The hybrid sols were prepared by hydrolysis and condensation of trimethoxy(7-octen-1-yl)silane (TMOS) and tetraethyl orthosilicate (TEOS) in the presence of acetic acid. Structural characterization of the hybrid coatings was performed using powder X-ray diffraction analysis (PXRD). The morphology of the coating has been studied by scanning electron microscope (SEM). Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests have been performed, and the results showed that the silane coatings had high corrosion resistance. The heat treatment of the coatings at various temperatures have been investigated, and the results show that 130^∘C is an optimized temperature. The results expose that the hybrid coating enhanced the corrosion protection of aluminum in aqueous 3.5% NaCl solution.

In this work, the surface of AISI 430 stainless steel was coated with a hyper-eutectic FeCrC and pure B₄C powders using the plasma transferred arc (PTA) welding method. Further, the microstructure, microhardness, and abrasive wear resistance of the coated layer were evaluated in this work. Hard coating layers were formed between 750HV and 1000HV from the PTA melting coating process with high energy input (due to PTA). Due to the addition of FeCrC and B₄C, the martensite, austenite, M₇(C-B)₃, M${}_{23}$(C-B)₆, Cr(C-B), FeCr, Fe₂B, Fe₃C, Fe₂C, SiC, and Fe₃(C-B) phases were formed in the coating layer which makes the layer very hard. The abrasive wear resistance of the coated layer was evaluated using the Taguchi method with L${}_{16}$ mixed-level orthogonal index. Samples, wear distance (m), applied load (N), and abrasive grain size (grid) were chosen as input parameters. The mass loss due to wearing was evaluated based on “the smaller the better”. All input parameters significantly influence the wear, but the highest effect was found with the wear (slip) distance. Also, a linear regression equation was obtained to estimate the mass loss between the parameters and the levels used.

Wrinkling patterns are beneficial for a wide range of engineering applications including flexible electronics, tuned optics, sensoring, energy harvesting, surface wetting and biomedicine. Here we report on controllable multimode wrinkling patterns of metal (iron) films sputter deposited on flexible substrates with gradient modulus. It is found that disordered wrinkles (G1 wrinkling) form in the weakly crosslinking region at the early stage of film deposition. Disordered labyrinth wrinkles with larger wavelengths and ordered stripe wrinkles localized by cracks (both G2 wrinkling) appear in the strongly crosslinking region for the samples with small film thickness and large thickness, respectively. The coexistence of the labyrinth G1 wrinkling and labyrinth G2 wrinkling (or stripe G2 wrinkling) can be obtained by tuning the substrate modulus and film thickness. The morphologies, evolutions and mechanisms of such wrinkles are discussed in detail based on the stress theory. This study can promote better understanding of the substrate effect on the complex wrinkling patterns.

In this study, Au–4H-$n$-SiC metal–semiconductor (MS) and Au–Al₂O₃–4H-$n$-SiC metal–insulator–semiconductor (MIS) devices were fabricated to examine the effects on the performance of electronic devices of interfacial insulating materials. In order to determine the dielectric properties, capacitance/conductance–voltage ($C/G$–$V)$ measurements were realized in a wide range of voltages ($-$3.0 V)–(11.0 V). Current–voltage ($I$–$V)$ measurements to obtain the electric properties were realized at $\pm 2.5$V. Moreover, both the energy distributions of surface states ($N_{\text{ss}})$ and series resistance ($R_s)$ were obtained from the $C/G$–$V$ data. Obtained results provided that series resistance originating from interfacial layer (Al₂O${}_3)$ was more effective on the $I$–$V$ and $C/G$–$V$ characteristics which must be taken into account in the calculation of main electrical parameters. The rectification ratio (RR) and shunt resistance ($R_{\text{sh}})$ of the MIS device were almost 10³ times greater than those of the MS structure. Using Al₂O₃ between Au and 4H-$n$-SiC also led to an increase in the value of barrier height (BH) and a decrease in the value of ideality factor ($n)$. These results confirmed that Al₂O₃ layer leads to an increase in the performance of MS device with respect to low values of $N_{\mathrm{\text{ss}}}$, reverse saturation current ($I_0)$ and $n$ and high values of RR, $R_{\text{sh}}$ and BH.

In this paper, we have studied the effect of variable-angle grooves and baffles on the mixing efficiency of the micromixer. In order to explore the influence on the micromixer with different types of grooves and baffles, we designed grooves and baffles with different geometric parameters and placed them in T-channels to interfere with fluid flow. We studied VAM30^∘ (variable-angle grooves and baffles micromixer with an angle of 30^∘) directions and distributions as well as their different groove depths and baffle heights affect the mixing performance. We tried to divide the grooves and baffles into five groups, and discussed the effects of staggered depth and height on mixing efficiency. The mixing efficiencies of micromixer in the Re (Reynolds number) range of 0.1–100 were calculated, and the fluid flow in the microchannel was analyzed. The simulation results show that VAM30^∘ is more favorable for solution mixing. The mixing efficiency of the micromixer could reach 98.9% with the change of different geometric parameters. This is because when the structure changes, the flow state of the fluid is improved, which is conducive to lengthening the residence time of the fluid in the channel. With the increase of Re, it is also conducive to enhancing the chaotic convection and improving the mixing efficiency.

Today, there is a rapid growing demand for graphite electrodes used at steel making factories. Graphite electrodes are expensive materials that are used at steel making factories. Increasing the working longevity of these materials can significantly improve the benefit of steel melting process. Therefore, the increase in the stability of graphite at high elevated temperatures in electric arc furnaces is necessary. The mixture of SiC/TiO₂/SiO₂ coating can desirably reduce the oxidation of the graphite matrix at high temperatures. Evidently, the SiC/TiO₂/SiO₂ coating can specially decrease the mass loss rate of the graphite at high elevated temperatures and improve its working longevity in these conditions. Moreover, this coating can effectively improve the stability and thermal shock properties of graphite at the temperatures up to 1000^∘C.