Surface Review and Letters

There remains a keen concern in magnesium (Mg) and its alloys, as they are the lightest available structural materials. Mg alloys are capable of allowing the design of lightweight engineered systems, including encouraging implications to curtail energy consumption. These alloys are also evolving available biodegradable materials and battery electrodes. Instead of the extreme historical Mg usage at present, several intrinsic drawbacks, including susceptibility to corrosion, poor formability, and low creep strength limit the extensive use of Mg alloys. This review provides an overview of ancient to modern advances in the study of Mg corrosion. It describes the effects of alloying elements and reinforcement in metal matrix composites (MMCs) on the corrosion resistance of Mg alloys. The frequent use of protective strategies and their limitations are discussed from the recent past to the current trend. This review is recognizing acquaintance gaps while also endeavoring to ascertain planned developments and guidelines.

Tool steels are extensively used in sheet metal forming dies in order to prolong the life of dies and reduce the cost of production. Powder metallurgy tool steels are also alternatively preferred because of their low-risk metallurgical behavior owing to their compositions by which bulk steel would be difficult to produce, such as high amount of carbides or high alloying elements. Such advantage is desired if the steel has a narrow range of fine grain sizes and is less metallurgically affected by the heat treatment process due to having large surface area of fine grains. In this study, ASP^® 2012 powder metallurgy steel containing high amounts of Si, Cr, Mo and W was selected for boronizing by the boron-giving thermochemical process. The boride layers on the surface of ASP^® 2012 tool steel were metallographically characterized by various characterization techniques including adhesion strength test, SEM and XRD. The effects of corrosion kinetics and chemical composition of steel on the amount and types of boride layers formed on P/M steel of ASP^® 2012 after powder-pack boriding were investigated. The results indicate that, according to the Rockwell-C indentation test, the best adhesion in the boride layer was obtained in samples borided at 850°C for 4 h, while the worst adhesion was obtained in ASP^® 2012 steel boronized at 950°C for 4 h. Corrosion rates of boronized ASP^® 2012 steel were decreased compared to nonboronized ASP^® 2012 steel.

The flow accelerated corrosion of H₂S media widely exists in chemical equipment and chemical pipe fittings. It can lead to equipment failure and cause safety accidents. In this paper, ultrasonic shot peening (USSP) was used to realize surface nanocrystallization of the 5Cr–0.5Mo steel specimens. It was found that strong plastic deformation occurred on the surface of the specimen, and dense nanoscale corrosion product film was formed. A closed flow accelerated corrosion test device with H₂S media was used to test the corrosion of the specimens. The experimental results showed that the corrosion current density of the specimen was decreased, the corrosion potential was increased, and the corrosion resistance was enhanced. However, with the increase of USSP duration, the density of the corrosion product film formed on the surface of the specimen was decreased, and the corrosion rate of the specimen was increased.

Aluminum 6061-T6 alloy is widely used in several manufacturing sectors like automotive, aerospace and marine industries owing to their unique characteristics of high strength to weight ratio, low density and supreme electrical and thermal conductivity. Some of the properties of Al 6061-T6, such as poor surface and tribological behaviors, make them unable to be used in critical parts. In this work, surface modification was performed for Al 6061-T6 using WS₂ solid lubrication through the electrical spark deposition technique. The deposition was conducted by altering three different parameters, that is, powder concentration (PC), spark-on time (ST) and gap voltage (GV), based on the Box–Behnken design of response surface methodology. Effects of these deposition parameters were investigated on various surface modification aspects, including deposition rate, surface roughness (SR), microhardness and layer thickness. Results exhibit that the WS₂ deposited surface significantly improved the surface characteristics. Material deposition rate predominantly increased with an increase in PC. Surface microhardness is enhanced by 9–20 times that of the base material. The lowest SR was attained at an intermediate level of PC with a low level of ST and GV. A minimum layer thickness of 32.12 $\mu$m at intermediate PC and high ST with low GV was achieved. The elemental and structural analyses confirmed that the formation of intermetallics, such as WO₂, WO₃, Al₂O₃ and Al₄C₃, was formed during electrical spark deposition.

The aluminum-based composites (AMCs) are known for a variety of functions like building, aerospace, automotive, marine, and aeronautical applications. In this research, Al-4032 alloy-based 6% SiC (by weight) composite has been fabricated using stir casting and the effects of prominent machining parameters on energy consumption and surface finish have been examined using carbide inserts in turning. Microstructures of as-cast specimens has been analyzed using the optical microscope, scanning electron microscopy, and energy-dispersive spectroscopy. The CNC turning has been performed at varying machining parameters like cutting speed, feed rate, and depth of cut, following an RSM-based design matrix. The desirability function approach has been employed to obtain the best combination of parameters for achieving the desired objectives. The experimental outcome demonstrates that the machined composite is considerably influenced by built-up edge (BUE) formation and interfacial bonding of particles. The result establishes that the inclusion of SiC in the Al-4032 matrix demonstrates improved mechanical properties and superior machined surface with the optimized turning operation.

Proper selection of bath additives is critical to the plating rate, phosphorus content and corrosion resistance of the nickel–phosphorus (Ni–P) alloy deposits. In this work, electroless Ni–P alloy deposition from an acidic bath using sodium hypophosphite as the reducing agent at relatively low temperatures (30°C and 60°C) was carried out in the presence and absence of urea additives. The effects of different concentrations of urea on plating rate and phosphorus content of the Ni–P deposits were studied. The results showed that the plating rate and the phosphorus content of the Ni–P deposits were largely dependent on the concentration of urea in the bath. The corrosion resistance of the Ni–P deposits was evaluated in aerated 3.5 wt.% sodium chloride (NaCl) solution using potentiodynamic polarization curves. It was found that the corrosion resistance of the deposits obtained from the bath solution containing 1 g/L of urea was the highest. In addition, cyclic voltammetry techniques were used to study the mechanism of electroless Ni–P alloy deposition in the bath. The results revealed that the addition of urea to the bath promoted the concentrations of adsorbed atomic hydrogen and sodium hypophosphite on mild steel surface, which markedly increased the phosphorus content of the Ni–P deposits. This work offers a new way that highlights the relation between the urea additives and phosphorus content.

By combining synchronous fluorescence (SF) spectroscopy and fluorescence polarization (FP) technology, a new spectral technique, termed synchronous fluorescence polarization (SFP) can be obtained. It inherits the advantages of both, such as high sensitivity, less sample demand, rapid detection, and so on. This concept has been proposed before without implementation details. In this work, a detailed implementation scheme of the technology is proposed, including the hardware requirements of the instrument, the measurement and calculation of the instrument correction factor G-factor, the spectral acquisition, the removal of inner filter effect (IFE), the removal of solvent background and the calculation and analysis of anisotropy. Furthermore, exploring the mechanism of quantum dots (QDs) as fluorescent sensor to detect heavy metal ions was taken as an example to introduce the application of the SFP method. Through detecting SF anisotropy, the mechanism of QDs probing ${\text{Hg}}^{2+}$ ion was explained. If an appropriate fluorescent polarization enhancer is chosen, SFP can be used for quantitative detection. This work provides a specific implementation scheme of the SFP technology for the first time, which expands the application of fluorescence technology.

All kinds of heavy metal ions and synthetic dyes in water will produce serious environmental problems and damage to the human body. Activated carbon (AC)/hematite (H; $\alpha$-Fe₂O₃) nanocomposites (ACH nanocomposites) have been prepared using a hydrothermal method in ferric citric alkaline solution. The microstructure, chemical composition and properties of as-prepared ACH nanocomposites were investigated, respectively. It has been proved that $\alpha$-Fe₂O₃ nanoparticles embedded on the surface of AC greatly improved the hydrophilicity of AC. Results further showed that ACH nanocomposites could be used as adsorbents to effectively remove ${\text{Cr}}^{6+}$ and ${\text{Cu}}^{2+}$ from wastewater. The sorption process for ${\text{Cr}}^{6+}$ and ${\text{Cu}}^{2+}$ ions met the pseudo-second-order equation. The maximum adsorption capacities of ${\text{Cu}}^{2+}$ and ${\text{Cr}}^{6+}$ by ACH were about 20 mg/g and 21 mg/g, respectively. In addition, some organic dyes such as methylene blue (MB) and rhodamine B (RhB) could also be degraded completely by ACH composites. Therefore, it is expected that ACH nanocomposites can be regarded as promising adsorbents and low-cost Fenton-like nanocomposites for the removal of pollutants from aqueous solution.

In this research, aluminum matrix composites reinforced with continuous carbon fibers (CFs) were fabricated using A356 aluminum alloy and PAN-based CFs by squeeze casting. For this purpose, CFs were first coated with a nickel layer using the electroless method and then the microstructure of the nickel–phosphorus (Ni–P) electroless coating was investigated. In the next step, composite samples reinforced with volume fractions of 5, 10, and 15 vol.% CFs coated with Ni–P coating were fabricated by squeeze casting at 60 MPa, and then microstructure and mechanical properties were examined. The results of the bending test on the composite samples indicated that the nickel coating had a significant effect on the flexural strength of the composite and increased the flexural strength by up to 30%. In addition, with the increase in the volume percentage of the fibers, the hardness of the samples increased while both the wear rate and the coefficient of friction decreased. Moreover, the best wear resistance was observed in the sample containing 15 vol.% as-coated carbon fibers. The Ni coating led to the formation of a mechanically mixed layer (MML) containing a fine mixture of metallic oxides and carbon thus enhancing the wear resistance.

This study investigated the supercapacitor performance of the MAPbI₃/MWCNT composite electrode produced by spin coating. The produced electrode’s structural properties and surface morphology were analyzed by FESEM, EDX, XRD, and FTIR. Filling the voids in the MWCNT structure by MAPbI₃ perovskite crystals increases the charge density but provides ease of charge transport. The supercapacitor electrode performance was determined using specific capacitances calculated from current–voltage measurements in the potential range of $-$0.5–2 V at 25, 50, 75, and 100 mV/s scan rates. The maximum specific capacitance was 845.03 F/g at 25 mV/s. The electrode’s capacitance ratios to the capacitance at 100 mV/s were calculated as 25.8%, 37.3%, and 54.6% for 25, 50, and 75 mV/s scan rates, respectively. Current–voltage cycles are important because they show that the electrode has a stable structure.

Carbidic austempered ductile iron (CADI) is a new type of wear-resistant material with high performance developed in recent years. The effect of austempered temperature on the microstructure and properties of high B-bearing CADI was investigated. Boron is an element that significantly interferes with the spheroidization process. When the boron content in CADI is high, the crystallization of spheroidal graphite in the as-cast microstructure is hindered, and its roundness, spheroidization rate, and volume fraction are significantly reduced. The results of its heat treatment process show that with the increase of austempered temperature, the volume fraction of residual austenite in the matrix increased, the size of acicular ferrite becomes coarser, and the ferrite also increases significantly, and the macroscopic hardness and wear resistance of the specimens gradually decreased.

To study the hydrophobic properties of Betula alnoides wood modified by alkyltrichlorosilanes, four alkyltrichlorosilanes with different chain lengths were used to prepare hydrolytic solutions by adding 0.25% (v/v) of alkyltrichlorosilane to anhydrous toluene, and the wood samples were immersed in the hydrolytic solutions for 4 h. The surface chemical compositions of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and Varian 640-IR Fourier Infrared Spectrometer (ATR-FTIR), the surface morphology of the samples was observed by scanning electron microscopy (SEM), and the wettability of the modified wood was investigated using an optical contact angle goniometer. The results demonstrated that treatment with alkyltrichlorosilanes introduced Si and low surface energies of –CH₂ and –CH₃ on the surface of Betula alnoides wood. The –CH₂ and –CH₃ content increased with the increase in chain length. Alkyltrichlorosilanes formed a different micro or nanoscale roughness on the surfaces of the wood samples. The water contact angles of all coatings of alkyltrichlorosilanes are greater than $131.3\pm 2.4^{\circ }$, and greater than $115.5\pm 0.9^{\circ }$ after 180 s. The water absorption decreases with the increase in chain length. The water absorption of the uncoated sample is $44.0\pm 1.9$ wt.%, while those of samples modified by MTCS and OTCS are $18.0\pm 0.9$ wt.% and $11.0\pm 0.0$ wt.%, respectively.

Friction stir processing (FSP), which was the advancement in the friction stir welding technique, is thought to be an economic approach to alloying in the solid state that can be used to make composites. In this study, FSP was carried out to produce AA7075 (B₄$\mathrm{\text{C}}+\mathrm{\text{T}}$iN) composite by varying the composition of the reinforcement particles. Microstructural analysis was carried out and the homogenous distribution of the reinforced particles on the surface of AA7075 alloy was ensured. X-ray diffraction studies were carried out to analyze the phases present after fabricating the hybrid surface composites. Microhardness test was performed on the specimens before and after the fabrication process. Grain refinement in the friction stir processed zones was evidently seen in the optical microstructures. The combined effect of the ceramic powders and grain refinement led to increase in the microhardness in the hybrid surface composites compared with the base AA7075 plate. A 33.87% increase in microhardness was observed in the sample AA7075 reinforced with 75% B₄C and 25% TiN. Wear testing was carried out at various loads (5, 10, 15 and 20 N) and at different sliding velocities (300, 350, 400 and 450 rpm) and the track distance was maintained at 1000 m. It was observed that the highest wear rate is $3.2\times 10^{-7}$ cm³/Nm for the base plate AA7075 and the sample AA7075 reinforced with 50% B₄C and 50% TiN shows the lowest wear rate of $0.56\times 10^{-7}$ cm³/Nm. It is observed that the addition of B₄C and TiN has resulted in a significant improvement in the wear resistance of the AA7075 alloy.

Drilling, which constitutes one third of the machining operations, is widely used in many areas of the manufacturing industry. Various difficulties are encountered in the drilling process since the chip is formed in a closed limited chip flows. These difficulties directly affect the output parameters such as energy consumption, surface quality, and cutting force. Therefore, it is necessary to determine the ideal processing parameters to achieve the best performance. However, experimental research on machining processes requires both a long time and a high cost. For these reasons, machining outputs can be estimated by conducting drilling simulations with the finite element method. In this study, the finite element method is used in order to investigate the influence of different cutting parameters and different helix angles on the power and thrust force of Ti–6Al–4V (grade 5) alloy that is commonly used in the aviation industry. The study selected three different cutting speeds, feed rates, and helix angles as the cutting parameters. The experimental design was made according to the response surface method (RSM) Box–Behnken design in the Design-Expert program. Drilling simulations were performed using the ThirdWave AdvantEdge^TM software. The lowest thrust force measured is 1241.39 N at 40° helix angle, 2000-rpm revolution rate, and 0.05-mm/rev feed rate, while the lowest power consumed is 765.025 W at 30° helix angle, 1500-rpm revolution rate, and 0.05-mm/rev feed rate. As a result, it was determined that the most effective parameter for power and thrust force was the feed rate.

Plasma electrolytic oxidation (PEO) was performed on 60 vol.% SiC_p/2009 aluminum matrix composite under different voltages in silicate solution and NaF solution, respectively. Anode gas evolutions under different conditions during the PEO process were evaluated by the gas chromatograph, optical emission spectroscopy, scanning electron microscope, X-ray diffraction and inductively coupled plasma atomic emission spectroscopy. The anode gas released at different voltages in both solutions contained H₂, O₂ and trace CO. The H₂ concentration increased with the increase of voltage in the silicate solution, and then it was kept at 75–80 vol.% in the range from $+$480 V/–0 V to $+$520 V/–0 V, which was related to the appearance of strong discharge sparks. The H₂ concentration of the anode gas in NaF solution was much lower than that in the silicate solution due to the weak discharge. The excessive H₂ was caused by nonfaradaic reactions in the plasma discharge region such as thermal decomposition of water. Meanwhile, the O₂ in anode gas mainly came from thermal decomposition of water in plasma discharge region and traditional electrochemical reactions in nondischarge region. In addition, SiC reinforcement particles were oxidized in plasma discharge channels with the temperature up to 5000 K, accompanied by the release of trace CO. Furthermore, CO₂ was hardly detected due to the effect of H₂ reduction in the discharge channels.