Surface Review and Letters

The bacterial spread can pose a significant risk in the transmission of infectious diseases. Nanomaterials, including synthetic antibacterial nanoparticles, have emerged as a promising solution to combat bacterial infections due to their unique physicochemical properties. Metal nanoparticles have been shown to exhibit potent antimicrobial activity against a broad spectrum of bacteria, including both gram-positive and gram-negative strains. One of the main advantages of using metal nanoparticles as antibacterial agents is their ability to penetrate the bacterial cell wall and disrupt cellular processes. This disruption can lead to the inhibition of bacterial growth and ultimately, bacterial death. Furthermore, metal nanoparticles can be engineered with specific surface modifications that enhance their antibacterial activity and improve their biocompatibility. These modifications can include the attachment of targeting ligands, peptides, or antibodies to the nanoparticle surface, which can increase their specificity toward bacterial cells and reduce their toxicity toward mammalian cells. Overall, the use of metal nanoparticles as antibacterial agents holds great promise for the development of novel therapeutic strategies to combat bacterial infections, both in vitro and in vivo. In this paper, we highlight the development of metal NPs, particularly those based on Mn, Fe, Co, Zn and Cu for their antimicrobial properties and related mechanisms.

In this work, the Metal Inert Gas (MIG) welding process is used for depositing the Inconel 718 over the base substrate of Stainless steel 321. The optimal welding conditions like 50% overlap, Direct Current (DC) plus mode with a pulse on time (1–5 s), frequency (0.25–1 Hz), peak current (120 A), base currents (60% of peak current), and speed (150–350 mm/min) are used for the successful hard-facing. The quality of the hard-facing is analyzed by conducting microstructural studies, tensile tests, microhardness, wear behavior, and electrochemical studies. Post-processing for wear and electrochemical studies is done by Scanning Electron Microscope SEM–EDX analysis. Microstructural studies revealed the presence of columnar dendrites and equiaxed at the top of the hard-faced layer. Hard-faced layer depicts the highest ultimate tensile strength of 772 N/mm² with an elongation of 31.50% due to the support of Nickel components. The presence of the voids and dimples is identified from the SEM fractography. The maximum hardness value of 212 HV${}_{0.5}$ is measured at the top of the hard face layer. The microhardness of the hard-faced layer increased by 17.77% higher than its base substrate. Because of the hard precipitates and higher microhardness made by the weld thermal cycle, the hard-face layer showed maximum Co-efficient of Friction (CoF) of 0.540. Debris and grooves are found with the SEM examination of the wear specimens. Higher impedance offers better corrosion resistance to the hard-faced layer Inconel 718. The EDX analysis confirms the presence of Chromium, Molybdenum, and Niobium contents at the hard-faced layer. These elements silently support better corrosion resistance compared to the base substrate of Stainless steel 321.

Due to their superior corrosion resistance at high temperatures, stainless steels have a wide range of applications in numerous industries (including chemistry, the petrochemical industry, the paper industry, and nuclear engineering), it is also utilized in the medical industry as an implant material. To enhance the outstanding qualities of stainless steel such as high temperature corrosion, surface coating methods are also used. Boronizing, nitriding, thermal spray coating, physical vapor deposition, chemical vapor deposition, and electro-spark deposition procedures are used to apply these coating processes to steel surfaces. The electro-spark deposition (ESD) coating technology is one of the most promising approaches in this area. Using high-frequency and high-current electric pulses, the ESD micro-welding procedure bonds electrode material to the surface of a metallic substrate.

In this study, AISI 304 and AISI 316L stainless steels were coated with FeAl and NiAl intermetallics using the ESD method. First, suitable experimental parameters for ESD coating were established. Second, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the microstructures and phases that formed on the coated surfaces. Then, the surface hardness of the resulting layers was determined. Finally, the corrosion properties of intermetallic-coated stainless steels were determined using electrochemical methods and compared with each other. As a result, both the hardness values and corrosion resistances of both stainless steel sheets have increased with intermetallic coatings.

In this study, La₂Zr₂O₇, Yb₂O₃ and Gd₂O₃-doped La${}_{1.4}$(Gd, Yb)${}_{0.6}$Zr₂O₇ thermal barrier coatings have been manufactured from the crystalline and amorphous feedstock by plasma spraying. The thickness of the bond coat is 100±25 $\mu$m and the thickness of the top coat is 250±25 $\mu$m. Thermal shock tests were carried out in furnace temperature of 1200^∘C. The thermal shock tests indicate that lifetime of the La${}_{1.4}$Gd${}_{0.6}$Zr₂O₇ coating has 55 cycles which is the highest thermal shock lifetime compared to other coatings in this study. The type of feedstock, amorphous or crystalline, strongly affects the thermal shock lifetime of La₂Zr₂O₇ coatings. Coating damage after thermal shock tests was investigated using scanning electron microscope to observe the microstructure and X-ray diffraction techniques to analyze the phase composition. The failure of coatings is mainly in consequence of the accumulation of stress between bond coat–ceramic coat interface due to thermal expansion coefficient differences and thermally grown oxide layer formation during thermal shock cycling tests.

Nanoparticles have the capability to augment the thermal conductivity of nanofluids. For the transmission of heat, the material’s low thermal conductivity is the key problem. Therefore, to increase the thermal conductivity, researchers mixed different nanoparticles in the base fluids. In this field of study, utilizing three different particles is the most recent strategy to form a ternary hybrid nanofluid that gives us better results in terms of heat transfer. The interaction of three different kinds of nanoparticles, i.e. copper, alumina and silver, is considered with water serving as the base fluid to form a ternary hybrid nanofluid. The paper explores the behavior of ternary hybrid nanofluids on heat and mass transportation phenomena of the two-dimensional magnetohydrodynamic (MHD) micropolar flow across a porous extending surface with zero mass flux and convective conditions. The Brownian motion, thermal radiation, heat source and sink, and joule heating are taken into consideration in the temperature equation. The chemical reaction is incorporated into the concentration equation. Appropriate similarity transformations are used to transform the system of partial differential equations (PDEs) to a coupled system of ordinary differential equations (ODEs). The homotopy analysis method (HAM) is used to solve the system of the flow equations. The effects of the nanoparticle’s volume fractions and other different physical parameters on the surface drag force, Nusselt number, velocities, microrotation, temperature and concentration profiles are scrutinized through figures and tables. The outcomes of the present investigation show that the heat transfer rate is augmented with the increasing value of thermophoresis parameter. The magnetic field has augmented temperature while the opposite result is seen in velocity and microrotation profiles. With the escalating values of thermophoresis parameter, the concentration and temperature of ternary hybrid nanofluids are boosted while the increasing Brownian and chemical reaction parameters have decreased the concentration profile. The surface friction coefficient exhibited by the ternary hybrid nanofluid is higher than hybrid and conventional nanofluids.

In this work, PVA/NaI consisting of polyvinyl alcohol (PVA) and sodium iodine (NaI) is irradiated using argon at fluence (45×10${}^{16}$, 90×10${}^{16}$, and 135×10${}^{16}$ ion/cm²). The structure is investigated by XRD technique. The influence of argon ion is studied theoretically by SRIM/TRIM simulations. The target vacancies are recorded 46/ion, target displacements are 47/ion, and the replacements atoms are 1/ion. Also, the dielectric properties were determined in the frequency of 100 Hz to 5 MHz. With an average fluence 90×10${}^{16}$ ions/cm², electrical conductivity and dielectric constants have increased to twice their initial value. Additionally, after being exposed to an ion beam, the dielectric loss is reduced to around half of its original value. For both the control and irradiation samples, the attenuation and half layers were estimated. The dielectric characteristics of the irradiated samples were found to improve. Numerous uses, including energy storage and batteries, are rendered possible by these results.

Conventional electroless Ni–B–Mo (ENB–Mo) deposits are formed using hazardous lead or thallium-containing solutions, which must be removed. In this study, ENB–Mo deposits were developed in a bath free of stabilizers and harmful heavy metals. This study estimates the effect of variation of coating bath temperature on tribological performance of ENB–Mo coating developed over AISI 1040 steel. The chosen bath temperatures were $85^{\circ }$C, $90^{\circ }$C, and $95^{\circ }$C to achieve ENB–Mo coating with varying B and Mo content. The 12–15 $\mu$m thick coating was uniform. In comparison to steel substrate, all of the coatings show enhanced corrosion resistance. In the as-deposited state, coatings were mixed amorphous and nanocrystalline with peak of Fe overlapping with Ni. Moreover, TGA results revealed that inclusion of molybdenum enhanced coatings thermal stability. The worn specimens at $300^{\circ }$C reveal development of shielding tribo-oxide coatings and existence of microstructural changes. At high working temperatures ($300^{\circ }$C), wear debris also has a major impact on tribological mechanisms of coatings. Correlation between microstructure, tribological behavior, and corrosion resistance have also been conducted for ENB–Mo coatings.

Inclined hole arrays on superalloys have important applications in aeroengines. However, defects occur during fabrication of inclined holes using thermal drilling methods, i.e. electrical discharge drilling (EDD), including a recast layer and microcracks on the hole wall. Therefore, abrasive water flow polishing (AWFP) of a superalloy inclined hole array machined via EDD was investigated in this study. Two types of specimens were designed: a hole array of identical size and a hole array with an identical inclination angle. The fluid simulation revealed that the fluid velocity and pressure on the lower edge of the inclined hole were significantly higher than those on the upper edge when the fluid flowed forward. The fluid characteristics exhibited opposite trends when backward flow was implemented. Time-division bidirectional flow can effectively compensate for flow field nonuniformity and improve material removal consistency during polishing. The experimental results show that for inclined holes with identical inclination angles, the size expansion decreases with an increase in the hole diameter owing to the lower fluid velocity and material removal volume in the relatively larger holes. Consequently, surface roughness Ra increases with hole size. For inclined holes with identical diameters, the size expansions of the entrance and exit approach the same level; whereas, Ra decreased with an increase in the inclination angle. The hole taper slightly reduced in all cases. Using garnet abrasives with 1300 mesh size, 1.5 wt.% abrasive concentration, and 3 MPa fluid pressure, the surface roughness Ra of target holes was reduced from pre-polishing $\ge$ 5.0 $\mu$m to approximately post-polishing 1.0 $\mu$m. The recast layer on the hole wall caused by EDD was completely removed.

Inconel 718 (IN 718) belongs to the category of nickel-based superalloys with outstanding mechanical characteristics such as high strength, better corrosion resistance, greater hardness, fatigue and wear resistance. This alloy is mostly implemented in manufacturing the components of aeroengines, nuclear reactors, space shuttles, pressurized boilers and so on. In most cases, the parts made from this alloy work in severe aggressive environments. A prolonged exposure of this alloy in such environments will pave the way for corrosion phenomenon which will minimize the service life of the components. It is reported that the parts made via additive manufacturing will exhibit better mechanical characteristics than the casted and forged parts. This work is aimed to investigate the anti-corrosion characteristics of both as-cast and LPBF printed IN 718 samples at various time intervals in the seawater environment. By means of FESEM micrographs, the microstructural evolution in both as-cast and LPBF printed IN 718 samples was analyzed. The anti-corrosion characteristics of both samples were investigated in the environment containing 3.5 wt.% NaCl (seawater) in terms of EIS and potentiodynamic polarization curves along with the corroded morphology. The results showed that the LPBF printed IN 718 samples exhibit fine cellular and columnar grains decorated with the NbC precipitates along their boundaries, whereas the casted samples have larger and coarser grains with uneven segregation of NbC precipitates. From the Tafel and EIS (Nyquist and Bode) plots, the LPBF IN 718 sample showed greater corrosion resistance in terms of current density and polarization resistance values. In particular, the 15 h LPBF sample has a strong, compact passive film formed on it. This compact passive film paved the way for this sample to exhibit lower current density (3.03 × 10${}^{-7}$ A/cm²) and higher polarization resistance (3678 Ω · cm²) when compared with the LPBF and cast samples at other intervals.