Surface Review and Letters

The physical health of human beings and the environment will be negatively influenced by the improper use of cutting fluid, which is an important factor for achieving sustainable machining. Turning is a basic process of all machining operations. Using a minimum quantity lubrication (MQL) system is the best way for achieving sustainable turning process. Improvements made in the MQL system to achieve better performance of the turning process have been discussed in this paper. Search categories that have been used to carry out the study are MQL system with the conventional cutting fluid, MQL system with nano-fluid, MQL system with cryogenics and restructured MQL system. The advancements in MQL turning process published over a span of four most recent years from 2018 to 2021 have been chosen for this review. In this study, the details of experimentation such as materials used for the workpiece, cutting tool materials, environments for lubrication, machining parameters, MQL fluids and performance parameters such as surface roughness, tool wear, cutting force, cutting temperature, etc. have been critically considered. Results investigated from various articles mostly show that advanced MQL systems such as MQL system with nano-fluid, MQL system with cryogenics and restructured MQL system are better than the conventional MQL system in terms of producing better output performance.

The strong adhesive strength is essential for the widespread applications of diamond coating in the mechanical field. In this paper, a novel method combining conventional chemical vapor deposition (CVD) diamond technique with solid particles was proposed to modify the interface material properties of substrate to improve the adhesive strength of the diamond coating. Prior to deposition, wet dispersion was adopted to uniformly distribute solid particles on the substrate, with which the diamond coatings with the WC, TiC and BN particles embedded at the interface were fabricated on Co-cemented tungsten carbide (WC-Co) substrate. In addition, the pure diamond coating was also fabricated for comparison. The as-deposited diamond coatings were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. The results indicated that the diamond coating with TiC exhibited the highest residual stress, which may be due to the larger lattice mismatch between TiC and diamond as compared to WC and BN. The indentation test suggested that WC and BN particles were favorable for the improvement of the adhesive strength and the crack resistance of diamond coating, while this phenomenon was not observed in the diamond coating with TiC particle. This might be caused by the large lattice parameter, high lattice mismatch, and high thermal expansion coefficient mismatch of TiC as compared with diamond. Furthermore, the lattice parameter of additional particles might be an important factor to determine whether or not the adhesive strength of diamond coating can be enhanced, because it determined the compressive stress or tensile stress generated inside diamond coating. Hence, interface modification of substrate by dispersing the solid particles with low lattice parameter or similar material properties of diamond may be an effective and convivence approach to improve the adhesive strength of the diamond coating.

It is critical to reduce the bandgap of a ferroelectric photovoltaic (FE-PV) material in order to get the optimal effect of FE-PV. The interface effect of PbO/PbTiO₃ (P/PT) is used in this work to lower the bandgap of PbTiO₃ via the addition of PbO. The bandgaps of (P/PT)_down and ${\text{(P/PT)}}_{\mathrm{\text{up}}1}$, which are two types of polarization structures, fall from 2.63 eV of pure PbTiO₃ to 2.07 eV and 2.08 eV, respectively. Densities of states are calculated for pure PbO, pure PbTiO₃, and P/PT to determine the reason of the bandgap drop. The results indicate that the PbO component of P/PT is critical for both the conduction band minimum (CBM) and valence band maximum (VBM) states. Calculations of the absorption coefficient indicate that P/PT absorbs more light over a wider range of wavelengths in the visible-light region than PbTiO₃.

Fused deposition modeling (FDM) is an extrusion-based three-dimensional (3D) printing technique that can find applications in communications, fashion, architecture, aerospace, automotive, medicine, and the education sector. The FDM printed part is affected by poor surface quality resulting from higher layer resolution and stair-stepping effects. Hence, this work aims at studying the effect of chemical treatment on the surface roughness, hardness, tensile strength, UV transmittance and tribological behavior of the acrylonitrile styrene acrylate (ASA) parts printed by the FDM process. Two different solvents namely, acetone and dichloromethane are considered for improving the surface finish of the ASA parts. The chemical treatment reduces the surface roughness, tensile strength, wear rate and improves the hardness by dissolving the external surfaces of printed specimens. The maximum surface finish and lesser UV transmittance are achieved from the sample treated with acetone. The higher hardness and low wear rate are noticed on the samples treated with dichloromethane.

Inconel 625 (IN 625) is a widely recognized nickel-based superalloy due to its high tensile strength, better fabricability, capability to prevent crack formation, acceptable corrosion resistance, etc. However, during the long-term usage, the formed oxide layers are converted into dichromates which reduce the anti-corrosion behavior. This study attempts to improve the anti-corrosion characteristics of IN 625 by cladding it with Colmonoy 6 particles. Further, the corroded morphology, microstructure, hardness and roughness were analyzed. Results showed that the cladded specimens are rich in dendritic and interdendritic areas. These areas are reported to contain rich carbides and borides of Cr that are formed after cladding. These precipitates paved the way for improving the hardness of the Colmonoy-6-cladded layer (7.54 GPa) when compared with the base material (4.49 GPa). A strong and continuous passive film was reported on the cladded samples during the corrosion test which protects the cladded layer. Further, EIS study also reported that the Colmonoy-6-cladded specimens experience higher polarization resistance values due to the stable passive film and lower $R_a$ values from the surface roughness measurements. Among the base and cladded samples, the 27-h cladded sample provides better corrosion resistance with greater $R_p$ (142,940). In addition, this sample has the minimum roughness ($R_a=2.761\mu$m) value than the other samples.

This paper presents the Toolox 44 steel’s experimental and statistical machinability optimizations conducted for achieving minimum output parameters (energy consumption ($E_c$), cutting force ($F_c$), surface roughness ($R_a$), and vibration (Vib)). Turning experiments have been performed under dry machining conditions on a CNC lathe at different cutting parameters according to the Taguchi L27 orthogonal array. Taguchi-based gray relational analysis (GRA) has also been used to optimize output parameters simultaneously. Moreover, analysis of variance (ANOVA) has been applied to determine the effects of cutting parameters on output parameters. As a result, the lowest Ec was measured 0.06 kW at the 1.5 mm depth of cut, 220 m/min cutting speed and 0.4 mm/rev feed rate. At 0.5 mm depth of cut, 220 m/min cutting speed and 0.1 mm/rev feed rate, the lowest $F_c$, $R_a$ and Vib are measured at 132.28 N, 0.69 $\mu$m and 2.25 m/s², respectively. According to GRA, the best machining combination in terms of energy consumption ($E_c$), cutting force ($F_c$), surface roughness ($R_a$), and vibration (Vib) was A1B3C1, and the percentage of improvement in the gray relational degree has been calculated to be 25.25%. Validation test results showed that the optimization of cutting parameters was successful in the machining process of Toolox 44 steel according to the multiple output parameter values.

Geological drilling required high-performance diamond drill bits. In this paper, diamond films were deposited on different drill bit substrates based on the MPCVD equipment. The properties of diamond films were analyzed by scanning electron microscopy (SEM), Raman spectra, X-ray diffraction (XRD) and tribological tests. The results showed that surface morphology of the four different substrates was good and the grain size was uniform. The diamond drill bit substrates include polycrystalline diamond compact (PDC), cemented carbide (WC–Co), impregnated diamond (IPD) and diamond thick-film welded (DT) sheets. The coefficients of friction of the deposited protective films are 0.15, 0.25, 0.23 and 0.29, respectively. What is more, the wear rates of protective films are $8.676\times 10^{-8}$, $13.491\times 10^{-8}$, $4.378\times 10^{-8}$ and $3.643\times 10^{-8}$mm³/N$\cdot$m, respectively. Addition of diamond films could effectively reduce the friction coefficient on the surface and improve the service life of drill bit.

This study investigated various performance measures — material removal rate (MRR), surface roughness (SR), and dimensional deviation (DD) — in wire cut electrical discharge machining of the Incoloy-800 superalloy under the effect of purposefully varied process inputs. Superalloys comprise a bright category of alloys that possess excellent mechanical strength at elevated temperatures, superior surface stability, magnificent creep resistance, and corrosion and oxidation resistance. Analysis of variance was performed to reveal influential and crucial inputs for machining measures; results were interpreted and modeled statistically. After conducting the experimental runs, the novel attempt has further been made to conduct the multi-response optimization with the desirability method and the teaching-learning-based optimization (TLBO) algorithm to develop the best process setting for optimizing all considered measures jointly. Furthermore, machined sample’s microstructure analysis was conducted with the scanning electron microscopy (SEM) analysis. The optimized parametric setting was obtained as follows: pulse on time: 2 $\mu$s, pulse off time: 4 $\mu$s, peak current: 2 A, and wire feed rate: 5 m/min. Obtained experimental values for MRR, SR, and DD were 0.936 mm/min, 3.797 $\mu$m, and 0.084 mm, respectively, with the combined desirability value of 0.601. Optimization values of MRR, SR, and DD through the TLBO method varied from predicted values by 3.01%, 6.86%, and 6.32%, respectively.

Tantalum oxide nanolayers with different thicknesses (30, 60, 90 and 120 nm) were deposited on glass substrates at a deposition angle of 60^∘ under high vacuum condition at room temperature by using electron gun evaporation method. The morphological, structural and optical properties of tantalum oxide nanolayers are investigated by XRD, FESEM, EDX, AFM and spectrophotometer. Kramers–Kronig relations are used to calculate the optical parameters. Optical results show that the real and imaginary parts of the dielectric function, the real part of the refractive index and bandgap energy have increased with increasing film thickness.

In this study, the metal inert gas (MIG) welding process is taken to deposit the Inconel 718 material on 321 stainless steel. Various modes like the DC, DC-pulsed, and DC-wave-pulsed modes in MIG welding are used for depositing Inconel 718. The primary parameters such as the welding current (90–120 A) and speed (150–350 mm/min) are varied within the range for making the layer deposition over 321 stainless steel. After performing the layer deposition, the dilution, contact angle, and peak temperature are analyzed to find the optimal MIG welding mode. From the macrograph, very low dilution (7.44%) is identified for the DC mode. The most inferior contact angle ($\theta$) of 49° was measured for the DC-wave-pulsed mode. The simulation work predicted a peak temperature of 2800°C for the DC mode. Considerable microstructure changes have occurred at the weld deposition (dendritic structure) and HAZ (grain coarsening) for all the three modes. At the top, interface, and HAZ locations, the microhardness obtained from the DC-pulsed mode is in between those of the DC and DC-wave-pulsed modes. Overall, the DC-pulsed mode is qualified for making the metal deposition and further work. For 50% overlap, defect-free 2-mm-thick layer depositions are made on the 321 stainless steel surfaces.

Manufacturing industries are always in search of preparing quality implants from Co–Cr–Mo biomaterial by doing improvements in their processes. CNC turning is basically adopted for preparing a practical surface of femoral head of hip implants. The online monitoring systems such as acoustic emissions (AEs) from the machining zone provide knowledge of the deformation characteristics of the work material in machining, which affect the machined surface topography and integrity. In this study, CNC turning experiments by using CBN insert were planned according to RSM CCD in dry cutting environment. Surface generation was monitored with the help of AE setup by correlating AE RMS voltage and counts to the surface integrity of machined surfaces. Cutting speed, feed rate and depth of cut show significant effects on the AE RMS voltage. The feed rate and depth of cut, however, also show dominating effects on the AE counts. It is also observed that at lower force components, the amplitude of AE RMS voltage corresponds to a lower surface roughness ($R_a=0.97$ $\mu$m) and the counts pattern of AE signal shows nonuniform behavior which corresponds to a higher surface roughness ($R_a=1.06$ $\mu$m); however, the smooth surface produced with a lower $R_a$ value (0.89 $\mu$m) shows uniform counts pattern of AE signals.

The goal of this work is to study the antibacterial activity of acrylic polymer/ZnO–Ag nanocomposite coating. First, in the presence of UV light ($\lambda =253.7$ nm), Ag nanoparticles (NPs; derived from AgNO₃ precursor) were photoreduced and deposited on the surface of nano-ZnO. Field emission scanning electron microscope (FE-SEM) images indicated that the AgNPs (5–15 nm) were deposited on the surface of nano-ZnO (20–40 nm). These ZnO–Ag nanohybrids (0.1–0.2 wt.%) were incorporated into the acrylic polymer matrix using ultrasonication to form the nanocomposite coating ($\sim 25$ $\mu$m thick). Nano-ZnO hybridized with AgNPs resulted in a decrease in the energy gap ($E_g)$ of ZnO from 3.2 eV to 2.7 eV, as observed by diffused reflectance UV–Vis spectrum analysis. The abrasion resistance test indicated that the incorporation of hybrid NPs enhanced the abrasion resistance of the polymer coating (from 81 to 125 l/mil). Moreover, the polymer nanocomposite coating showed high antibacterial efficacy against $E$. coli and $S$. aureus in antibacterial tests and achieved 1.8 and 1.2 log after 24 h, respectively. These findings endorse that the ZnO–Ag nanohybrid-based water-borne nanocomposite coatings offer exceptional antibacterial efficiency and would be promising in this application.

To improve the corrosion resistance of X70 pipeline steel in seawater, nickel coating was prepared on the surface of X70 steel by electroplating method. The corrosion properties of the samples in simulated seawater were studied by macroscopic electrochemical experiment and micro-scanning electrochemical experiment. The systematic characterization of the samples was conducted using a scanning electron microscope (SEM), energy disperse spectroscopy (EDS), and X-ray diffractometer (XRD) techniques. The time-dependent model was established to simulate the localized corrosion by COMSOL Multiphysics. The characterization results show that the nickel coating prepared at 0.045 A is compact and thickest. In the macroscopic electrochemical results, the impedance value of the nickel layer prepared at 0.045 A is 34% and 36% higher than that of the other two coatings, and the current density is 25% and 66% lower than that of the other two coatings. In the micro-scanning electrochemical results, the impedance value of the nickel layer prepared at 0.045 A is 5% and 40% higher than that of the other two coatings, and the current density is 14% and 26% lower than that of the other two coatings. Therefore, 0.045 A is the best electroplating current for preparing nickel coating. The simulation results show that the micropores on the surface of nickel-plated X70 are easy to induce localized corrosion, and the degree of localized corrosion decreases with the increase of micropore diameter.

This work investigates the fabrication of microholes in carbon-fiber-reinforced polymer (CFRP) composite by powder-mixed microelectrical discharge drilling (PM$\mu$EDD) method. Initially, pilot experiments were carried out to understand the effect of powder concentration on the machining time and material removal mechanism. Then the full-factorial experimental analysis was performed to investigate the micromachining performance of CFRP composite. The input factors considered for the full-factorial analysis were powder concentration (2, 4, and 6 g/L), capacitance (100, 1000, and 10,000 $\mu$F), and tool rotation (300, 400, and 500 rpm). The regression analysis was carried out to assess the significance of the chosen input factors. The surface morphology of the fabricated microhole was extensively studied to establish the material removal mechanism and failure mechanisms of the composite constituents.

Passive micromixers utilize no external energy input. It mainly depends on the structure change of microchannel to produce chaotic convection effect, which increases the contact surface and contact time between the fluid. The mixing efficiency of stagger non-abreast baffles (SNB) micromixer and stagger abreast baffles (SAB) micromixer is compared at five kinds of Reynolds (Res). It may affect the mixing efficiency including the height ($H$) and number ($n$) of baffles, the distance between two adjacent baffles, non-abreast baffles, and abreast baffles. As the $\theta$ of the baffles changes, it contributes to enhance the chaotic convection of the micromixer. When Re $=1$, the worst mixing efficiency of the most efficient seven SABs ($\theta =15^{\circ }$, $H=0.09$ mm, $D=0.60$ mm, $n=7$) micromixer reaches an astonishing 98%. The concentration change along the microchannel is studied in this paper. At low Re, SAB makes fluid contact zigzag in microchannel and enhances molecular diffusion. At high Re, SAB causes chaotic convection in the microchannel and completes the mixing quickly.