Surface Review and Letters

Superalloys go through cyclic oxidation which refers to the progression of reputed exposure of materials to alternating oxidizing and non-oxidizing environments at high temperatures. The oxidation behavior of cobalt-based superalloy coatings depends on several variables, including the environment, surface roughness, manufacturing conditions, & coating composition. Because of their higher temperatures and protective oxide layer, coatings with a greater cobalt concentration are more oxidation-resistant. The behavior of oxidation is influenced by surface roughness, where rough surfaces offer greater surface area to oxidation while smooth surfaces decrease interaction with the environment. The microstructure and porosity of the coating are further impacted by processing variables used in thermal spraying, including temperature, particles velocity, and spray distance. Adding reactive components to the coating composition, such as silicon and aluminum, and applying post-treatments like nitriding or sealing are two ways to increase oxidation resistance. A greater temperature and particle speed can lead to a denser with less porous covering, improving the oxidation process resistance. The two typically used heat spraying techniques are high-velocity oxy-fuel (HVOF) and plasma spraying. To increase the resistance to oxidation of thermal spray cobalt-based superalloy coating, some strategies have been devised, such as inclusion of reactive materials, such as aluminum and silicon, which is the coating composition. These elements may establish an oxide layer protecting the coating’s appearance, preventing further oxidation.

The configurations, electronic, and magnetic properties of the H₂DBP-M clusters have been investigated via density functional theory. The results reveal that the TM atoms for the H₂DBP-M ($\mathrm{\text{M}}=\mathrm{\text{Sc}}$, Y, Zr, Nb, Lu, and Hf) clusters deviate from the center planes of the clusters. The H₂DBP-M ($\mathrm{\text{M}}=\mathrm{\text{Sc}}$, Y, and Lu) clusters display the largest dipole magnitudes. Based on the binding energy per atom and HOMO-LUMO gap, the H₂DBP-Ni and H₂DBP-Lu clusters are the most favorable for synthesis. The charge transfer amounts of the TM ($\mathrm{\text{TM}}=\mathrm{\text{Sc}}$, Zn, Y, Cd, Hf, and Hg) atoms for the H₂DBP-M clusters are larger. The TM-d orbitals of the H₂DBP-M ($\mathrm{\text{M}}=\mathrm{\text{Ti}}\sim$Co and Cu) clusters contribute significantly to the Fermi levels. The spin densities of the TM atoms for the H₂DBP-M clusters reduce to 0 except for that ($V=2.459|\mathrm{\text{e}}|$) of the H₂DBP-V clusters.

This investigation focuses on the study of the effect of process parameters like peak current ($I_p)$, base current ($I_b)$, pulse frequency ($F)$, shielding gas flow rate ($Q)$ on mechanical properties like yield strength (YS), ultimate tensile strength (UTS) and flexural strength (FS) of the welded joints during pulsed TIG welding of SAILMA 450 and EN14 B steels. Taguchi’s L${}_{25}$ orthogonal array has been used for conducting the tests. Multi-objective optimization has been performed using Grey relational analysis (GRA) in order to maximize the mechanical strength and to find out the optimal set of parameters. The optimum parametric combination is obtained at a peak current of 220Amps, base current of 120Amps, pulse frequency of 5Hz and shielding gas flow rate of 17l/min. Analysis of variance (ANOVA) is used to predict the significant process parameters. It has been observed from the ANOVA analysis that peak current and pulse frequency have more influence on the output responses than the shielding gas flow rate and base current. The results of the confirmatory test show an improvement of 0.5801 in the GRG, which is satisfactory. A microstructure study has been performed using scanning electron microscopy (SEM) for the optimal set of process parameters.

$\beta$-In₂S₃ thin films ($\mathrm{\text{S/In}}=1$, 2 and 4) were prepared using the pneumatic spray pyrolysis (PSP) route to analyze the effect of the S/In ratio on the physical properties. These properties were conducted using the photothermal deflection spectroscopy (PDS) method. The PDS signal amplitudes as a function of wavelength show multiple reflections which appear for all prepared In₂S₃ films. Such multiple reflections indicate homogeneity and high crystalline quality of the films. The deduced values of the optical band gap vary in the range 2.55–2.65eV. The highest thermal diffusivity is obtained for $\mathrm{\text{S/In}}=2$. The product ($\mu \cdot \tau$) is found in order of 10${}^{-8}$cm${}^{-1}$/V. The estimated carrier diffusion lengths are 0.06, 0.11 and 0.09$\mu$m for films corresponding to $\mathrm{\text{S/In}}=1$, 2 and 4, respectively. Defect absorption in $\beta$-In₂S₃ films is also investigated by PDS. Five absorption peaks are observed. These absorption peaks contain defect information in the band gap. Hence, this work evidences that $\beta$-In₂S₃ is a multi-functional material that can be used in optoelectronic, photovoltaic and visible-irradiation photocatalyst applications.

Public transport via trams has become increasingly important in daily life to meet the growing demand for economic and environmental considerations. In order to ensure the safety of the railway system and reduce service costs, it is necessary to understand the tribological behavior of the system. There are various types of damage such as fatigue, wear, and cracking that can harm the wheels and rails. To determine the wear mechanisms and identify the situations in which wear movements occur, it is crucial to monitor factors such as temperature, surface roughness, and contact micro-hardness between the wheel and the rail. The objective of this study is to analyze the tribological behavior and the impact of climatic conditions on the wheel–rail contact system in the desert area of the Ouargla tramway in Algeria. To achieve this, an intelligent sensor programmed by a microcontroller was utilized to measure the temperature of the wheel–rail contact. Additionally, a hardness tester was used to measure the micro-hardness of the rail, and a roughness tester was utilized to monitor the surface condition of the rail. The measured temperature values during the passage of the tramway varied between ambient temperature and a temperature of 450^∘C. The micro-hardness values ranged from 270 Hv to 440 Hv, and the roughness values varied between 0.4$\mu$m and 2.7$\mu$m.

This study delves into the realm of M70, high-performance concrete (HPC) with a focus on enhancing its mechanical and sustainable properties through the incorporation of nanomaterials, specifically nanosilica, and organic composites derived from abaca fibers. HPC is pivotal in contemporary construction for its superior durability, strength, and resistance to environmental factors. The integration of nanosilica aims to refine the microstructure of the concrete at the nanoscale, enhancing its strength and durability. Simultaneously, the introduction of organic composites from abaca fibers seeks to impart eco-friendly characteristics to the concrete mix, addressing sustainability concerns. The research methodology involves systematically varying the proportions of nanosilica (0%, 0.5%, 1.0%, 1.5%) as a partial replacement for cement in the concrete and additionally, abaca fibers (0%, 0.25% and 0.5%) were used to enrich the durability. Mechanical testing will be conducted to assess the impact of these additives on the concrete’s structural performance, while durability testing will focus on resistance to environmental factors such as moisture and chemical exposure. The outcomes of this study enriching the concrete performance and optimization of high-performance concrete (1% of nanosilica and 0.25% of abaca fiber) is the superior quality compared to all other mixes.

This paper explains about the mechanical insertion of graphite particles into aluminum (Al-1100) surface for forming composites on the surface through an electrical resistance heat-supported pressing procedure. The surface of the aluminum is first graphite coated by solution casting. To achieve impregnation, the graphite–aluminum interface is locally heated with the assistance of electrical resistance heating followed by mechanical pushing. The degree to which aluminum surface softens can be regulated by process factors like current and heating time. Microstructural characterization of aluminum–graphite composite was carried out with SEM, TEM, Raman spectroscopy and XRD. It was revealed from the microstructural characterization that graphite particles were impregnated into the aluminum surface without agglomeration. Raman spectroscopy of graphite-impregnated surface shows a shift in major graphite peaks and an increased ratio of intensity ($I_D/I_G$). The presence of carbide compound (Al₄C₃) was not detected from the XRD and TEM studies. The mechanical property examination of the surface was carried out by nanoindentation and the subsurface was characterized by microhardness tests. It was observed that surface mechanical property and reduced Young’s modulus were improved by more than 200% and 150%, respectively. The projected method can be utilized as a surface modification technique in solid-state by fabricating surface composites fabricated through mechanical insertion of particulate reinforcement at sub-melting temperatures of substrate and under an open producing environment.

Micro-electro-discharge drilling ($\mu$EDD) is a type of non-traditional machining process used for drilling micro-holes of desired dimensions with a high aspect ratio. But, there are no such research works that could have explained the desired accurate circular shape of micro-holes. The need for a more advanced hybrid machining process to improve the overall efficiency in terms of mainly desired circular shape and radial overcut is evolved. In this research work, an electromagnetic field force-assisted micro-EDM process has been carried out on Inconel 800 with a copper tool of 450$\mu$m. Experimental results showed that measured metal removal rate and tool wear rate decreased for ascending values of magnetic flux density, peak current and gap voltage, whereas circularity increases linearly with an increase in magnetic flux density and also the effects of magnetic field on circularity of micro-holes on Inconel 800 are more predominant than other parameters.

In this study, Bi alloy AA1100/TiO₂/AA5083 composites were produced by accumulative press bonding (APB) for the first time. In the first step, two bars of aluminum alloys 1100 and 5083 with 5wt.% of uniformly scattered TiO₂ particles were stacked together and pressed with a 50% reduction ratio. Then, this process was continued up to six steps. Corrosion properties of composites were studied by potential dynamic polarization and electrochemical impedance spectroscopy measurement in 3.5wt.% NaCl solution. So, in this investigation and as its novelty, a considerable improvement was revealed in the main electrochemical parameters as a result of enhancing the influence of APB steps and the inert character of the particles. Moreover, using the wear test, the wear resistance of these bi alloy composites has been studied vs the APB steps. Also, the wear and electrochemical experiments showed that corrosion and wear resistance of samples were improved by the APB steps by 70% and 34%, respectively.