Surface Review and Letters

A high-velocity oxygen fuel (HVOF)-sprayed NiCrBSi coating on H13 hot work die steel was processed with laser remelting; and the surface-interface morphologies, concentrations of chemical elements, and phases of the coating were analyzed with scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), respectively. The friction-wear behaviors of the coating at high temperatures were investigated by the means of ball/plane contact. The effects of high temperature on the coefficient of friction (COF) and wear performance are discussed. The results show that the coating is dense and tightly bonded to the substrate at the interface. The average COFs at 500${}^{\circ }$C, 600${}^{\circ }$C, and 700${}^{\circ }$C are 0.3749, 0.3609, and 0.4556, respectively. The wear mechanism is slight adhesive wear at 500${}^{\circ }$C, and primarily oxidative wear and fatigue wear at 600${}^{\circ }$C. The wear mechanism at 700${}^{\circ }$C is oxidized wear and fatigue wear in the early stage, and mainly adhesive wear in the later stage. During high-temperature wear, an oxide film is formed on the coating surface, decreasing the wear resistance of the coating, which is primarily dependent on the compounds of Ni, Cr, B, Si, and C and the oxides of Si.

Co₃O₄ decorated flower-like g-C₃N₄ hybrid nanocatalysts were successfully synthesized and prepared via a facial hydrothermal method. The composition and morphology of the as-synthesized Co₃O₄/g-C₃N₄ nanocatalysts were characterized by the techniques of XRD, FT-IR, SEM, TEM, XPS and N₂-sorption. The analysis results indicated that the as-synthesized samples possess the flower-like structure, which consisted of g-C₃N₄ nanosheets and Co₃O₄ nanoparticles with the size about 25nm. The as-prepared Co₃O₄/g-C₃N₄ catalysts possess high catalytic activity and excellent stability for carbon monoxide (CO) oxidation. The total conversion of Co can be kept for more than 48h under the reaction temperature of 120${}^{\circ }$C.

In order to enhance the photodegradation of organic pollutants, Boron-doped tin dioxide (B-doped SnO₂) composite films with narrowed band gap were successfully prepared by the sol–gel method. The samples are characterized by UV–Vis absorption spectroscopy, photoluminescence (PL), X-ray diffraction (XRD), high-resolution field emission scanning electron microscope (FE-SEM), X-ray energy dispersive spectroscopy (EDS), and Brunauer–Emmett–Teller (BET). UV–Vis absorption spectroscopy results revealed that the absorption of the B-doped SnO₂ film was clearly broadened to the visible light area. PL results showed that the recombination rate of the photo-generated species was effectively prohibited by B doping. The photocatalytic properties of the films were evaluated by degradation of organic pollutants including acid naphthol red (ANR) dye and formaldehyde solutions. Experimental results indicated that the B-doped SnO₂ film exhibited an excellent photocatalytic activity under visible light irradiation due to its strong visible light response and diminished electron–hole recombination.

Electrical discharge machining (EDM) of a stack allows achieving high precision and quality of cut surfaces and, therefore, this method is indispensable for state-of-the-art mechanical engineering. The procedure of EDM is carried out with wire-cutting machines. The characterization of constructive parameters of a stack of material and applying of an efficient cutting regime are the most important preconditions providing high precision of EDM. The goal of this work is the improvement of quality and efficiency of wire electrical discharge machining (WEDM) technology by theoretical and experimental studies of the WEDM process. The subsequent development of theoretical and empirical models allowing for the calculation of the quality parameters of treated surfaces is realized. It is shown that the main characteristics of cut surfaces are the roughness, size precision, error profile and structure of a surface layer. For the first time, the regression dependencies between the main parameters of the WEDM process (pulse $on$-time $t_{\mathrm{\text{on}}}$, off-time $t_{\mathrm{\text{off}}}$, the height of the stack and the physicomechanical properties of the cut materials are obtained. The experimental study of WEDM confirms the results of mathematical modeling. It is proved experimentally that at an interlayer gap higher than 0.1mm, the cutting process stability is decreasing whereas the probability of the electrode fracture is increasing. However, it is found that at $t_{\mathrm{\text{on}}}=21\mu$s and $t_{\mathrm{\text{off}}}=60\mu$s, a stable cutting regime leading to bundling of the stock materials made from steel 65Γ can be realized.

In the present study, microarc oxidation (MAO) coatings were formed on ZL101A aluminum alloy in an electrolytic bath containing 3g/L KOH $+$ 2g/L Na₂WO${}_4+$ 4g/L KF. The morphology and wearing behavior were investigated. In both electrolytes, the additives were borates (Na₂B₄O₇18g/L) and silicates (Na₂SiO₃ 18g/L), respectively. It was found that the coating formed in borates-containing electrolyte was of compact and smooth structure than that of the one formed in silicates-containing electrolyte at the optimum treatment time. It was found that all the coatings were composed of á-Al₂O₃ and ã-Al₂O₃. The microhardness and wear tests proved that the coating formed in borates-containing electrolyte was having better mechanical properties than those of the coating formed in silicates-containing electrolyte.

Gemini surfactants are presently gaining attention due to their unusual self-assembling characteristics and incomparable interfacial activity. Current research work involves the cost-effective microwave (MW) synthesis of waste soybean oil-based gemini imidazolinium surfactants (GIS) having a carbonate linkage in its spacer moiety. Structural characterizations of the materials have been done using FT-IR, ¹H-NMR and ${}^{13}$C-NMR. Using indigenous and natural material as base and MW as energy source for synthesizing the GIS with easily degradable chemical moiety make them to be labeled as green surfactants.

Ni–TiN thin films with different TiN nanoparticle contents were successfully fabricated from a nickel bath with the addition of four TiN nanoparticles loadings (2, 4, 6 and 8g/L). The influence of the TiN nanoparticle content on the film structure, micro-hardness, micro-strain and residual stress was examined, and the film wear behavior was investigated in detail. The results showed that the average size of the nickel grains and TiN nanoparticles is 68.1nm and 22.6nm, respectively, for the film deposited with 8g/L TiN. X-ray diffraction patterns indicated that the film deposited with 2g/L TiN displays the (2 0 0) preferred orientation; however, when the concentration of TiN in the bath was increased to 6g/L, such orientation was suppressed and a random arrangement showed up. The film wear loss gradually decreases as the concentration of TiN additive in the bath increases from 2g/L to 8g/L, and a minimum loss of approximately 39.7mg was obtained for the film deposited at 8g/L TiN, which also displayed the maximum average micro-hardness (789.4HV).

The main purpose of the current research work is to identify and investigate a novel method of holding an intermediate metal and to evaluate its metallurgical and mechanical properties. Copper was used as an interlayer material for the welding of this dissimilar Ti–6Al–4V (Ti alloy) and 304L stainless steel (SS). The study shows that the input parameters and surface geometry played a very significant role in producing a good quality joints with minimum heat affected zone and metal loss. A sound weld was achieved between Ti–6Al–4V and SS304L, on the basis of the earlier experiments conducted by the authors in their laboratory, by using copper rod as intermediate metal. Box–Behnken method was used for performing a minimum number of experiments for the study. In the present study, Ti–6Al–4V alloy and SS304L were joined by a novel method of holding the interlayer and new surface geometry for the interlayer. Initially, the drop test was used for determining the quality of the fabricated joint and, subsequently, non-destructive techniques like radiography and C-scan were used. Further optical micrograph, SEM–EDS, hardness and tensile test were done for understanding the performance of the joint.

Effects of film thickness and electrolyte concentration on the photovoltaic performance of TiO₂-based dye-sensitized solar cell (DSSC) were studied. Nanocrystalline anatase TiO₂ thin films with varying thicknesses (3.2–18.9$\mu$m) have been deposited on FTO/glass substrates by screen printing method as work electrodes for DSSC. The prepared samples were characterized by UV-Vis spectroscopy, Atomic Force Microscopy/Scanning Tunneling Microscopy (AFM/STM) and X-ray diffraction (XRD). The optimal thickness of the TiO₂ photoanode is 13.5$\mu$m. Short-circuit photocurrent density ($J_{\mathrm{\text{sc}}}$) increases with film thickness due to enlargement of surface area whereas open-circuit voltage decreases with increase in thickness due to increase in electron diffusion length to the electrode. However, the $J_{\mathrm{\text{sc}}}$ and $V_{\mathrm{\text{oc}}}$ of DSSC with a film thickness of 18.9$\mu$m (7.5mA/cm² and 0.687V) are smaller than those of DSSC with a TiO₂ film thickness of 13.5$\mu$m (9.9mA/cm² and 0.734V). This is because the increased thickness of TiO₂ thin film resulted in the decrease in the transmittance of TiO₂ thin films hence reducing the incident light intensity on the N719 dye. Photovoltaic performance also depends greatly on the redox couple concentration in iodide$\setminus$triiodide. $J_{\mathrm{\text{sc}}}$ decreases as the redox concentration increases as a result of increased viscosity of the solution which lowers ion mobility. Similarly, $V_{\mathrm{\text{oc}}}$ decreases as the electrolyte concentration increases due to enhanced back electron transfer reaction. An optimum power conversion efficiency of 4.3% was obtained in a DSSC with the TiO₂ film thickness of 13.5$\mu$m and redox concentration of 0.03mol dm${}^{-3}$ under AM 1.5G illumination at 100mW/cm².

Nanocomposite Ni–Zn coatings containing 80 wt.% Al₂O₃, 5 wt.% Y₂O₃ and 15 wt.% graphene were fabricated by pulsed electrodeposition method in nickel–zinc sulphate-based electrolyte and effects of pulse current parameters on nickel and other element contents, microstructure, resistance to corrosion and tribological properties of the coatings were investigated. The pulsed current with duty cycle from 10% to 50% was applied to different samples and frequency changed gradually from 500 to 4000Hz in five steps during coating process. Increasing the duty cycle led to decrease of absorbed nanoparticles in the surface of the coatings from 4.4 vol% to 3.58 vol% The sample coated with 10% duty cycle had utmost alumina content in the coating surface, 3.5 vol% in first layer up to 4.4 vol% in fifth layer. The sample coated with 30% duty cycle had higher corrosion resistance with passive current density of 2.5mA/cm². Furthermore, the results showed that by increasing the duty cycle, wear rate had been increased up to 1.3$\times$10${}^{-6}$mm²/N$\cdot$m.

Grand canonical Monte-Carlo simulation was carried out to study the effect of linker functionalization by Li atoms. In this work, two new Li-doping structures, MOF-808-Li and MOF-808-OLi were theoretically constructed by physical modification and chemical modification, respectively. The results show that both these methods can improve the hydrogen storage performance significantly, owing to the Li atoms increasing the interaction energy between the hydrogen molecules and the Li-doped MOF-808. Furthermore, MOF-808-OLi shows higher hydrogen capacity in comparison to the H₂ adsorption in the MOF-808-Li, this can be attributed to the new adsorption sites created by oxygen atom. The gravimetric adsorption capacity of MOF-808-OLi can reach 3.17wt.% at 77K and 1bar, which are significantly higher than the hydrogen adsorption in the unmodified MOF-808.

Thermally sprayed coating is commonly used to modify the surface to improve the mechanical properties of the substrates to meet their functional requirements. Numerous research works were carried out to assess the suitability of the WC–Co coating for industrial applications using thermal spray process. Meanwhile, few researchers expressed about the deterrent effect of the decarburization on mechanical properties of the coating due to processing at high temperature in thermal spray process which reduces the efficiency of the coating process. In this research work, coating of WC–12%Co powder over ASTM A36 steel substrate through plasma spray process was considered to investigate the effect of introducing the carburization process on wear properties of the resultant coating. Carburization process was introduced on the ASTM A36 steel substrate before the application of the plasma spray coating to compensate the loss of carbon during the process. Characterization of the deposited coating was done by scanning electron microscope, X-ray diffraction, hardness, corrosive resistivity test and wear tests. The results of the tests indicated that introduction of the carburization process remarkably increased the hardness of the coating and corrosive resistivity besides improving the wear resistance.

This paper deals with the effects of shielding gas mixtures (100% CO₂, 100% Ar and 80 % Ar $+$ 20% CO${}_2)$ and heat input (3.00, 3.65 and 4.33kJ/mm) on the mechanical and metallurgical characteristics of AISI 410S (American Iron and Steel Institute) super martensitic stainless steel (SMSS) by gas metal arc welding (GMAW) process. AISI 410S SMSS with 1.2mm diameter of a 410 filler wire was used in this study. A detailed microstructural analysis of the weld region as well as the mechanical properties (impact, microhardness and tensile tests at room temperature and 800${}^{\circ }$C) was carried out. The tensile and impact fracture surfaces were further analyzed through scanning electron microscope (SEM). 100% Ar shielded welds have a higher amount of $\delta$ ferrite content and due to this fact the tensile strength of the joints is superior to the other two shielded welds.

Amorphous molybdenum oxide films with almost 20$\mu$m thickness are electrodeposited on the Cu foils from a citrate-ammonia molybdate bath containing Ni${}^{2+}$ ions. The content of Ni in the oxide films is very low, 0.87 at.%. XRD and FTIR data suggest that they are composed of hydrous MoO₂. The multilayer and cracked structures are characterized by scanning electron microscopy (SEM), and are beneficial to transmission of Li${}^{+}$ ions between the electrolyte and anode materials. Galvanostatic battery testing shows that amorphous molybdenum (IV) oxides as anodes for lithium-ion batteries exhibit a high specific capacity of 876mA$\cdot$h$\cdot$g${}^{-1}$ at a current density of 50mA$\cdot$g${}^{-1}$, good capacity retention as high as 97.4% after 20 cycles.

A four-ball tester was used to evaluate the tribological performances of bismuth naphthenate (BiNap), sulfurized isobutene (VSB), and their combinations. The results show that the antiwear properties of BiNap and VSB are not very visible, but they possess good extreme pressure (EP) properties, particularly sulfur containing bismuth additives. Synergistic EP properties of BiNap with various sulfur-containing additives were investigated. The results indicate that BiNap exhibits good EP synergism with sulfur-containing additives. The surface analytical tools, such as X-ray photoelectron spectrometer (XPS) scanning electron microscope (SEM) and energy dispersive X-ray (EDX), were used to investigate the topography, composition contents, and depth profile of some typical elements on the rubbing surface. Smooth topography of wear scar further confirms that the additive showed good EP capacities, and XPS and EDX analyzes indicate that tribochemical mixed protective films composed of bismuth, bismuth oxides, sulfides, and sulfates are formed on the rubbing surface, which improves the tribological properties of lubricants. In particular, a large number of bismuth atoms and bismuth sulfides play an important role in improving the EP properties of oils.

Influence of MgO+CeO₂ on the microstructure and hardness of the WC–Ni-based alloy coating, manufactured on AISI 1045 by vacuum melting, have been investigated. It was found that suitable addition of MgO+CeO₂ can effectively reduce the pores within the coating, can refine the grain size of the WC hard phase and makes it get distributed uniformly. The hardness of the coating was enhanced with the addition of MgO+CeO₂. It reached the maximum value of 920HV at the addition of 0.4% MgO+0.4% CeO₂. Excess addition of MgO+CeO₂ can result in many defects in the coating during the solidification process. The coating with the addition content of 0.4% MgO+0.4% CeO₂ was shown the most excellent property. The related mechanism is also discussed.