Surface Review and Letters

Welding, despite being the most efficient joining process, has significant negative impact on the environment and worker health. This paper presents the environmental impact of various conventional welding processes and sustainability of Friction Stir Welding–a Green technology which requires no filler material, no shielding gas, no flux and involves no gas emissions. It is an energy-efficient process that saves significant amount of power and energy when compared to conventional welding processes. The defect-free welds produced have better mechanical and metallurgical properties than other processes. The higher temperature distributed due to the friction heat is established as the source of weld failure. Cooling the weld joint controls the heat conduction thus further enhancing the weld properties. This review paper explores the different cooling techniques employed for cooling the joint during Friction Stir Welding process. The changes in temperature distribution and microstructure caused by the cooling applied and the consequential transformation in material flow, tensile strength, hardness, corrosion, wear, residual stress are discussed. The changes in weld properties obtained by using different cooling media on different materials are reviewed.

A TiNiCoCrVSi high entropy alloy (HEA) coating was prepared on Ti–6Al–4V alloy by laser cladding. Then, the microstructure, phase composition, hardness, wear resistance and high-temperature oxidation resistance of the prepared coatings were investigated. The wear behavior of the TiNiCoCrVSi coating against a Si₃N₄ ball was evaluated under dry sliding conditions. The high-temperature oxidation resistance was tested at 800^∘C. The results show that the phase structure of the TiNiCoCrVSi coating was mainly composed of a body-centered cubic (BCC) (Ni,Co)Ti₂ and (Ti,V)₅Si₃. The TiNiCoCrVSi coating has a high hardness, and the highest surface hardness was 1357 HV. The wear volume of the coating was 1/7 of that of Ti–6Al–4V. The wear mechanism was abrasive wear and oxidative wear. The TiNiCoCrVSi coating exhibited good high-temperature oxidation resistance at 800^∘C. A dense oxide film (TiO₂, Cr₂O₃ and NiCr₂O₄) was formed on the surface of the coating. The dense oxide film prevented oxidation. The high-temperature oxidation resistance of the coating was 1/12 of that of the substrate.

Ag₃PO₄ and MoS₂ semiconductor materials were synthesized by hydrothermal method. The composite materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), and UV–vis diffuse reflectance spectroscopy (UV–VIS DRS), and the photocatalytic degradation of organic dyes by rhodamine B was studied. The results showed that: Ag₃PO₄/MoS₂ composite photocatalyst is formed by using MoS₂ microspheres as the matrix and Ag₃PO₄ nanoparticles coated on its surface or embedded in its lamellar structure. When the molar fraction of Ag₃PO₄ in the composite product is 75%, the composite photocatalyst has better light absorption capacity and lower photogenerated carrier recombination rate (optical band gap is 1.24 eV), and shows better visible light photocatalytic degradation activity in the photocatalytic degradation of RhB experiment, the catalytic degradation rate is as high as 95.0%. At the same time, the degradation mechanism showed that H⁺ and O²⁻ were the main active substances for RhB degradation. The photocatalyst has excellent performance and simple preparation method. It has broad application prospects in the field of photocatalysis.

This study focused on determining the effects of the cooling condition in the conventional and ultrasonic-assisted turning of AISI 52100 steel. AISI 52100 steel has been widely used in the bearing, mold, and automotive industries because of its superior wear resistance and mechanical properties. However, its high wear resistance caused poor machinability in conventional machining methods. Low surface quality, rapid tool wear, high cutting temperature, and high cutting force are the main difficulties in the conventional machining of AISI 52100 steel. On the other hand, ultrasonic-assisted machining has become widely used in the past decades for the machining of materials that have low machinability in conventional methods. Conventional turning and ultrasonic-assisted turning were selected as machining methods. Ultrasonic-assisted turning experiments were conducted under 20 and 30 kHz vibration frequencies. Cubic Boron Nitride (CBN) cutting tools were used in machining experiments. In machining operations 50, 100, and 150 m/min cutting speeds were selected, and feed rate (0.1 mm/rev) and depth of cut (0.5 mm) were kept constant in experiments. Minimum quantity lubrication technique which used 1% Al₂O₃ nanoparticle additives cutting fluid and dry cooling methods were used. CBN insert was used as a cutting tool. The effects of cutting speed, cutting method, and cooling condition on surface quality, cutting force, cutting zone temperature, and cutting tool wear were studied experimentally. Analysis of Variance (ANOVA) was carried out to determine the significance of the effects of input variables on process outputs. As a result of this study, it is determined that combined UAT and nanoMQL have significant effects on the process outputs.

Friction Stir Processing (FSP) is a promising solid state method and it is developed from the Friction Stir Welding (FSW) principle. FSP was employed to enhance the surface characteristics by ceramic particulate reinforced with AA5052 aluminum alloy. Initially, the machined square grove was formed on AA5052 and packed with ceramic particulate. In this research, chromium carbide (Cr₃C₂) is a ceramic material for improving the surface characteristics of the base material. The FSP parameters such as tool rotational speed, traverse speed and axial forces were utilized in this process. The microstructure evolutions of the processed specimens were observed by optical microscope and Field Emission Scanning Electron Microscope (FESEM) with Electron Dispersion Spectroscopy (EDS). The mechanical properties like processed microhardness and tensile strength of AA5052 friction stir processed specimens were analyzed. The various microstructural zones were observed in the processed regions with dispersion of the particulates Cr₃C₂. The specimen fabricated at 1000 rpm tool rotational speed, 25 mm/min traverse speed and 7 kN axial force exhibits maximum microhardness and tensile strength with homogeneous dispersion of Cr₃C₂.

The machinability of a cutting tool merely depends on cutting temperature, surface finish, and tool life, etc. To investigate the machinability of non-textured plain cutting inserts and micro-textured cutting inserts, various novel micro-textures have been fabricated using a femtosecond laser machine on the rack face of the double-sided square cutting insert without amputating its TiCN coating. The turning operation has been performed on a Titanium Gr 2 rod of diameter 50 mm on a three-jaw self-centered lathe machine. Type of insert, rotational speed, and cutting feed rate are the main parameters with various levels. L27 orthogonal array has been used for the design of experiments. Significant reduction in cutting tool temperature and surface roughness has been observed using micro-textured cutting inserts. The cutting insert with Honeycomb micro-texture gives superior results with a minimum cutting temperature of 210^∘ C and a maximum of 76% improvement in surface finish.

Fabrication of surface features like effusion holes on ultra-high temperature (UHT) alloys with micro electro-discharge machining ($\mu$-EDM) is a very convolute strategy. Due to the exceptional mechanical properties and resistance to ease brittle transformation at elevated temperatures, UHT alloys are being widely used in hot sections of aero engines. This research tailored the existing capabilities of $\mu$-EDM setup by employing a copper-tungsten (Cu-W) hybrid tool electrode which has been rarely reported. This research addresses investigations, predictive modeling, and optimization during $\mu$-EDM of UHT alloy, namely Inconel 718. For experimentation, the factors like inter-electrodes gap (IEG), current ($I$), and pulse on/off time ($T$_on, $T$_off) were considered as input variables to analyze the responses like overcut (OC), tool wear rate (TWR), material removal rate (MRR), and diametric alterations in between the top and bottom shape of holes’ feature (DE). The multi-objective desirability-based artificial bee colony optimization (MOABC) projected optimal parametric settings of 5.276 A, 16.389 $\mu$s, 1.77 $\mu$s, and 50 $\mu$m for $I$, $T$_on, $T$_off, and IEG, respectively. These settings provide MRR, TWR, OC, and DE solutions of 0.001479, −0.00038, 0.030239, and 0.047048 mm, respectively. Further, the confirmation test has been performed to validate the optimal solution. The results supported the ideal settings with error values of 0.03177, 1.31578, 0.05863, and 0.04704 for MRR, TWR, OC, and DE, respectively. Distinctive diagnostic tests assessed by several statistical parameters ($P$, $F$, $R$², AD-P values) confirmed that the accuracy of developed models for prediction of various performance characteristics has high degree of resemblance with experimental results and the adequacy as well as accuracy of models is also demonstrated. Moreover, the surface morphology has also been scrutinized by microscopical observation to perceive the consequences of the electro-discharge phenomenon on both electrodes. Overall, the research comprises experimentation, surface integrity study, and parametric optimization followed by a confirmation test to perform the betterment of the current $\mu$-EDM approach.

ZnO${}_{(x)}$–Co₃O${}_{4(1-x)}$($x$= 0.7, 0.5, 0.3) oxide thin films were synthesized via spray pyrolysis deposition. The obtained films were investigated to find the surface electrical resistance ($R$) and conductance ($G$) using the four point probe device and the Van der Pauw mathematical relation to estimate the electrical resistivity ($\rho$) and conductivity ($\sigma$). In addition, the electrical resistance, conductance, resistivity and conductivity were obtained. From the obtained results, we have observed that the electrical quantities of the nanocomposite films are close to the interval bounds of the electrical quantities of the pure materials. For example, at room temperature, the electrical resistivity values of ZnO, Co₃O₄, ZnO${}_{(0.7)}$–Co₃O${}_{4(0.3)}$, ZnO${}_{(0.5)}$–Co₃O${}_{4(0.5)}$ and ZnO${}_{(0.3)}$–Co₃O${}_{4(0.7)}$ were found to be around 6.89 × 10${}^{-2}$, 1.58−10³, 339.75, 611.55 and 1333.632 Ω.cm, respectively. This note can be depending on the density (concentration) of the carriers (electron/holes) of the constituents (pure material) of the composite material. Besides, the variations of these quantities were measured as a function of the substrate temperature. It was found that the conductance and conductivity vary proportionally with the temperature, but the electrical resistance and resistivity were inversely proportional. This remark indicates a semiconducting electrical behavior. The possible reaction mixture of pure semiconductors materials in the synthesis process is explained. The studied semiconductor oxides show interesting electrical properties, which makes them potential candidates to be used in various optoelectronic devices.

Zr-containing silica residue (Zr-s-r) is waste residue discharged during the industrial production of ZrOCl₂. Its purified product (Zr-s-r-P) can be used as an adsorbent whose main component is amorphous SiO₂. Herein, Pb(NO₃)₂ solution was used as wastewater containing Pb${}^{2+}$. The adsorption of Pb${}^{2+}$in water by Zr-s-r-P and its mechanism were studied. The results showed that the adsorption effect was affected by the initial concentration of Pb${}^{2+}$in the solution, pH, and adsorption time. The adsorption capacity of Zr-s-r-P to Pb${}^{2+}$was 45.3 mg/g under the optimized conditions (25^∘C, pH=6, Zr-s-r-P dosage of 2 g/L, and adsorption time of 25 min). The process of adsorption fits the pseudo-second-order model, and the isothermal adsorption fits the Langmuir adsorption model. Pb${}^{2+}$was adsorbed in the pores of Zr-s-r-P. Moreover, the adsorption of Pb${}^{2+}$by ZSR-P was achieved through the reaction between Si–OH on the surface of SiO₂ and Pb${}^{2+}$ hydroxyl compounds.