Surface Review and Letters

Since the last two decades, many novel techniques have evolved from electro-discharge machining (EDM). Among them, surface modification is one of the rigorously growing technologies by which surface properties can be enhanced by providing a layer having a thickness up to some microns on the workpiece. Existence of tool material on the machined surface after EDM was observed previously. This attribute of EDM makes it a benchmark in surface modification technology. Surface modification in EDM can be done by using different types of electrodes like solid, powder metallurgy (P/M), brush type, etc. This phenomenon can also be acquired by suspending powder particles into dielectric media. However, P/M electrode gives superior results with less effort and also proves to be economical. In this paper, a review has been made on using P/M electrode in surface modification during EDM. The different types of electrodes for surface modification, development of P/M electrode, types of layers generated and surface roughness improvement are critically analyzed. Also, some scope for future works is suggested here.

Layer-by-layer (LbL) self-assembly is one of the unique methods for fabrication of ultra-thin film. This technique has immense application aross many fields in today’s life. In this paper, we have presented the fabrication of the thin film comprising of antifungal and antibacterial cationic dye methylene blue with negatively charged E. coli K30 bacterial polysaccharide sharing with PAH. The multilayers were characterized by UV–Vis absorption spectra and AFM. Various photophysical behaviors were investigated. Such studies provide a new light in the research of layer by layer self-assembly technique.

Nano-fluidic devices have great potential in the applications of biology, chemistry, and medicine. However, their applications have been hampered by their expensive or complicated fabrication methods. We present a new and simple approach to fabricate low-cost two-dimensional (2D) nano-mold based on ultraviolet (UV) lithography and wet etching. The influence of UV lithography parameters on the width dimension of AZ5214 photoresist was investigated. With the optimized parameters of UV lithography, the width dimension of photoresist patterns had sharply decreased from microscale to nano-scale. At the same time, the influences of etching time on the over-etching amount of SiO₂ film and nano-mold depth were also analyzed for further reducing the width of nano-mold. In addition, the effect of photoresist mesas deformation on the nano-mold fabrication was also studied for improving the quality of nano-mold. By the proposed method, trapezoid cross-sectional 2D nano-mold with different dimensions can be obtained for supporting varied applications. The minimum nano-mold arrays we fabricated are the ones with the dimensions of 115nm in top edge, 284nm in bottom edge, and 136nm in depth. This method provides a low-cost way to fabricate high-quality and high-throughput 2D nano-mold.

Anatase-phased TiO₂ films were prepared at different temperatures (350, 400, 450 and 500^∘C) using automated nebulizer spray pyrolysis (ANSP) method. The structural study (XRD) revealed the amorphous nature at 350^∘C and remaining samples (400, 450 and 500^∘C) show the tetragonal structure with 2${\theta }^{\circ }=25.78$, 38.43, 48.49 and 55.54 corresponding to (101), (004), (200) and (105) reflected planes and it is well fitted with standard data. The compositional XPS analysis confirmed the core level primary element of Ti 2p, O 1s and valance band (VB) of Ti 3p, Ti 3s, O 2s peaks in the prepared samples. The 3D optical profilometer has shown that the thickness of the prepared films was decreased by increase in temperature. The AFM study exhibited average roughnesses (Ra) of the prepared films such as 0.058, 0.147, 0.176 and 0.194nm, respectively. The surface morphological study of FESEM has shown the cracked uneven distributed nature (350^∘C) turn into evenly distributed closed packed agglomerated particles by the influence of temperature. The oscillating nature of transmittance (%) with redshift of the sharp absorption edge was observed in UV–Vis–NIR spectrophotometer and found the bandgap value about 3.58eV to 3.33eV through Tauc’s relation. The gas-sensing behavior has shown better response to C₂H₆O reducing gas at 300^∘C operating temperature with 150 ppm gas concentration.

The structural and phase transformation of microarc oxidation (MAO) coatings on 6061 aluminum alloy at 300^∘C/3MPa steam were evaluated. After 10 days steam corrosion, the weight loss of coated alloys with 15$\mu$m and 75$\mu$m thickness was only about 1/10 and 1/50 of weight gain of bare alloy, respectively. The $\gamma$-Al₂O₃ and $\alpha$-Al₂O₃ phases in the MAO coatings were stable at 300^∘C/3MPa steam, but many fine needle-like or brick-like boehmite crystalline particles also appeared on coating surface. The boehmite had a large influence on the permittivity of coatings at low frequency. The MAO treatment on 6061 aluminum alloy improved its corrosion resistance at high-temperature and high-pressure steam.

Pure and nickel doped copper sulfide (CuS) nanostructure were prepared by hydrothermal method for 5 h at $150^{\circ }$C. Structural, morphological and optical properties of the CuS nanostructure were studied for different Ni-doping concentration of 1%, 2%, 3%, 4%, and 5 %. X-ray diffraction studies showed the polycrystalline nature with hexagonal phase structure of CuS and Ni: CuS nanostructure. FE-SEM image showed that nickel doping concentration affected the nanostructure morphology. The absorbance spectra were then recorded at wavelengths ranging from 350 nm to 1000 nm, where the CuS nanostructures have strong absorbance in the NIR. The optical band gap energy of the samples increased as nickel concentration increasing. In particular, their optical band gap energies were 3.25, 3.48, 3.49, 3.49, 3.45 and 3.44 eV for undoped and Ni-doped CuS nanostructure with concentrations (1%, 2%, 3%, 4% and 5%), respectively. The antibacterial activity of Copper sulfide nanostructure against P. aeruginosa, E. coli, and S. aureus was evaluated by zone of inhibition. The test revealed that copper sulfide nanostructure have a strong antibacterial activity against gram-positive than for gram-negative with low concentration of CuS.

Oxygen evolution reaction (OER) is of great importance in splitting water. However, the sluggish OER kinetics at the anode severely hinders the H₂ evolution at the cathode which is a crucial procedure for energy storage. Herein, we report the synthesis of a new OER catalyst of Co(OH)_x(WO${}_4{)}_y$ via a one-step hydrothermal method, where the incorporation of WO${}_4^{2-}$ as a condenser greatly enhanced the electrocatalytic activity of Co(OH)₂ toward OER. Moreover, the introduction of mesoporous carbon (MC) further improves the electrocatalytic performance of Co(OH)_x(WO${}_4{)}_y$ by forming the nanocomposites of Co(OH)_x(WO${}_4{)}_y$/MC. The synergism between Co(OH)₂ and WO${}_4^{2-}$ and the synergistic catalytic effect of Co(OH)_x(WO${}_4{)}_y$ and MC majorly contributed to the apparently enhanced electrocatalysis of Co(OH)_x(WO${}_4{)}_y$/MC toward OER. This work provides an efficient strategy to improve the electrocatalytic activity of Co(OH)₂ by introducing WO${}_4^{2-}$ and forming nanocomposites between Co(OH)_x(WO${}_4{)}_y$ and MC for low-cost, convenient and highly efficient water oxidation.

Laser surface alloying was employed to enhance the wear resistance of 304 stainless steel with pure tungsten powder. The effect of laser fluence on phase constituents, microstructure, hardness and corrosion properties was investigated. It is found that the laser fluence has a direct correlation with the phases present in the coatings. Intermetallic Fe₇W₆ phase was found in the composite coating due to the metallurgical reaction of W with the Fe, Cr and Ni elements in the melting pool. Coatings with composite microstructure in nature were obtained resulting from the dilution of substrate and the laser-induced rapid cooling process. Intermetallic phase of Fe₇W₆ with solid solution of Ni and Cr shows dendrite or hallo structure depending on the laser fluence. Sintering and/or consolidation of W particles is observed for samples processed with lower laser fluences. It has been found that hardness of the coatings was improved significantly compared with the 304 stainless steel substrate. Coating processed with laser fluence of $2.5\times 10^7$ J/m² shows the best corrosion resistance.

The fabrication of microchannels, in order to dissipate the heat flux generated in the complex parts of an electronic industry, requires considerable attention since it is a complex process. Some advanced machining process like wire electrical discharge machining (WEDM) has been employed carefully for forming channels in material. However, the surfaces of these microchannels play an important role in dissipating heat energy. The present study focusses on the fabrication of AA6351/10wt.% Rutile MK grade mineral through powder metallurgy route, and their properties are evaluated. In addition, the forming of microchannels on the fabricated composite has also been done through WEDM process under varying machining conditions. WEDM process conditions considered are current, voltage and wire speed, and the response characteristics are kerf width, surface roughness and kerf depth. The hybrid approach of gray-based Taguchi coupled with PCA has been considered for optimizing the process parameters so as to get near net shape channels. The determined hardness of the composite is 64.5HB and the compressive strength is 220MPa. The optimized conditions are predicted and the regression model has been developed.

In this study, four excessive worn brake rotors of a light commercial vehicle are coated using different thickness, methods and powder coatings. Coated rotors ($R1$, $R2$, $R3$ and $R4$) compared with OEM brake rotor ($R$0) in terms of friction coefficient ($\mu$) and braking noise. Three braking test procedures (bedding, hot judder I and II) are applied to five rotors using inertia brake dynamometer. Results in bedding testing procedures showed that $R0$ rotor provided higher brake noise and higher $\mu$ compared with coated rotors. In hot judder I testing procedures, $R4$ rotor provided higher $\mu$ and higher brake noise compared with the other coated rotors and $R0$. Also, in hot judder II testing procedures, $R2$ rotor provided higher $\mu$ compared with the other rotors, $R0$ provided higher brake noise compared with the other coated rotors. In addition, based on experimental data, noise levels are estimated by multiple regression method with dummy variables.

In this paper, Yb:LuScO₃ crystal was processed by chemical mechanical polishing (CMP), and the surface roughness of 0.18nm was obtained. The atomic step structures of these sesquioxide crystals are successfully characterized by AFM scanning probe technology. Through several CMP experiments, the basic material removal mechanism of a ytterbium-doped LuScO₃ crystal during CMP is studied. Based on the findings, a material removal model is established. The results of this study provide ideas for the study of CMP, crystal growth and epitaxy.

The contemporary trend of cost-saving is the primary motive while studying the relative motion between the material surfaces. Therefore, exceptional surface characteristics are the most desirable features for any material. The rapid emerging surface modification phenomena like Friction Stir Processing (FSP) have proved its potential in the surface engineering applications. In this study, Magnesium–Aluminum–Silicon (Mg–Al–Si)-based AS21A magnesium alloy was examined for the wear characterization in respect with the cast and Friction Stir Processed (FSPed) conditions. FSP, performed at an optimized set of parameters, was utilized to attain the surface modification in the investigated material. In the wear study, cast and FSPed conditions of AS21A specimens were examined on Pin-on-disc apparatus with typical load values ranging from 10–40N. The subsequent investigation involves characterization of worn surfaces through Scanning Electron Microscope (SEM) micrographs, and Energy Dispersive X-Ray Spectrometer (EDS) to understand the accountable wear mechanism. It was found that the FSPed AS21A samples exhibited noteworthy improvement in the wear characteristics at all assessment conditions. FSPed sample showed overall 17% enhancement in the specific wear rate. Also, with an increase in normal load, around 53–55% reduction was observed in the Coefficient of Friction (COF) value. It was established that the morphology of Mg₂Si precipitates had an active contribution in the wear behavior of cast and FSPed AS21A samples. The notable mechanisms found responsible for the wear of samples were adhesion, abrasion, oxidation, delamination and plastic deformation.

Pitting corrosion of carbon steel in sodium chloride solution induced by Ce${}^{3+}$ and the synergistic inhibition effects of Ce${}^{3+}$ and Zn${}^{2+}$/SiO${}_3^{2-}$ were investigated using in-situ observation and electrochemical methods. The results showed that the presence of Ce${}^{3+}$ could result in severe pitting corrosion and a positive shift in the corrosion potential. It was found that individual Ce${}^{3+}$, Zn${}^{2+}$, or SiO${}_3^{2-}$ had low inhibition efficiencies, whereas the combination of Ce${}^{3+}$ and Zn${}^{2+}$ or SiO${}_3^{2-}$ proved to be highly effective in inhibiting the development of pits in two different ways and in enhancing the corrosion resistance. The pitting corrosion and inhibition mechanisms were discussed based on the results.

The magnetic properties and microstructures of electrodeposited Co–Ni–Fe–Gd thin films have been investigated for various concentrations of Mn. Nanocrystalline Co–Ni–Fe–Gd alloy thin films were deposited by electrodeposition method on copper substrate with different concentrations of Mn. Microstructures of the deposited Co–Ni–Fe–Gd films were investigated with scanning electron microscope (SEM) and different morphologies such as one-dimensional flower-like crystallites and two-dimensional plate-like crystallites were observed. The Co–Ni–Fe–Gd alloy films exhibit both soft and hard magnetic properties as the Mn ion concentration is varied and the best soft magnetic character is obtained when Mn concentration is 0.1 M, which may be a good candidate for MEMS and recording media.

This paper presents the tribological examination of various percentages of montmorillonite nanoclay-filled polyester composites and jute fiber reinforced hybrid composites by the Pin on Disc wear testing method. The wear rate and coefficient of friction were investigated for each composition with the working parameters like applied load (10,20,30N), sliding speed (3m/s), and sliding distance (1500m). The reduction in the wear rate was found on the inclusion of 5wt.% clay and 25wt.% jute fiber and further addition of fiber changes the trend due to the reduced matrix concentration. The wear mechanism of the worn-out surface samples was studied using scanning electron microscopy.