Key Engineering Materials Vol. 993

Abstract: Layered double hydroxides (LDHs) materials are widely used in the cathodes of high-performance supercapacitors. However, current preparation methods suffer from issues such as high energy consumption, complex processes, and significant safety hazards. In this study, based on a mild biomineralization reaction route, flower-like nano-sheet structured cobalt-based LDHs (COH) cathode was successfully prepared. The COH cathode achieved an outstanding specific capacitance of 829.0 F g^-¹ at a current density of 1 A g^-¹ and retained 90.9% of its initial capacitance after 4000 cycles. This biomineralization strategy holds promise for widespread application in the preparation of nanostructured electrode materials.

Abstract: Aluminum-air batteries have gained significant attention due to their high theoretical energy density, cost-effectiveness, and environmental friendliness. However, challenges such as voltage drops and capacity losses from aluminum electrode corrosion necessitate innovative solutions. This study explores the use of neutral electrolytes and the alloying of aluminum with magnesium (Mg), tin (Sn), and gallium (Ga) to enhance battery performance. The electrochemical properties of Al-Mg-Sn-xGa alloys (x = 0, 0.1, 0.25, 0.45) were investigated. The addition of Ga reduced discharge potential and increased discharge capacity by dissolving the oxide film on the electrode surface. Potentiodynamic polarization tests and scanning electron microscopy confirmed the superior electrochemical properties of the Al-Mg-Sn-Ga (0.25 wt%) alloy. These findings suggest that a Ga content between 0.25 and 0.45 wt% is optimal for Al-Mg-Sn alloy-based aluminum-air batteries, providing insights for designing high-performance batteries.

Abstract: A series of boro-tellurite glasses having chemical compositions: 50B₂O₃ - 35TeO₂ - 10Bi₂O₃ - (4.5-x)Na₂O - 0.4Nd₂O₃ - xYb₂O₃ where x = 0.1, 0.2, 0.3, 0.4, and 0.5 mol% were fabricated and characterized in order to study the effect of Nd/Yb substitution in boro-tellurite glass in absorption spectra. These glasses have been completely fabricated by applying the melt-quenching method. Fabrication was carried out by raising the furnace temperature from room temperature to 500°C for 10 minutes, then holding it for 10 minutes, and raising it again to 950°C for 35 minutes. Absorption spectra were measured at room temperature using a Hitachi VHS300 UV-Vis Spectrophotometer. From the experiment, it revealed that nine absorbance bands were found: i.e., 513, 526, 584, 627, 681, 746, 802, 874, and 976 nm.

Abstract: The more applications involving gamma radiation, the more protection and prevention are needed to avoid its negative impact. Glass as gamma radiation shielding is widely developed. In this study, tellurite glasses were prepared using composition 70TeO₂ - (15-x)ZnO - 10Bi₂O₃ - 3Na₂CO₃ - 2Ho₂O₃ - x Nd₂O₃ (with x = 0, 1, 2, 3 mol%). These glasses were fabricated by the standard melt-quenching approach. The effect substitution of Nd₂O₃ on tellurite glasses was discussed in terms of physical (Density and Molar Volume (V_m)) and gamma radiation shielding properties. With the addition of Nd₂O₃ concentration, the density of tellurite glasses increases from 6.17 to 6.25 g/cm³ due to the higher molecular weight of Nd₂O₃. The gamma-ray shielding properties were investigated by simulating through the Phy-X PSD program within the energy range from 10^-3 to 10⁵ MeV. The results show tellurite glass with 3 mol% of Nd₂O₃ provides the highest Mass Attenuation Coefficient (MAC). Moreover, at energy 1 MeV the Mean Free Path (MFP) and Half Value Layer (HVL) values were 2.586 cm and 1.793 cm. It was found that adding Nd₂O₃ reduces the MFP and HVL values of tellurite glasses. Based on the analysis, it can be determined that Ho/Nd codoped tellurite glass with 3 mol% of Nd₂O₃ is the most suitable glass for gamma-ray shielding application.

Abstract: Friction stir welding is an ecological and innovative solid state joining process of metallic materials, representing a current research direction of international interest. Submerged Friction Stir Welding (SFSW) is an unconventional joining technique, derived from the FSW welding process, which has generated considerable interest in the international scientific community as well as in industrial fields producing different welded metal components and modules/structures. The paper presents the results of the experimental research carried out by ISIM Timisoara regarding the FSW welding in air and in liquid working environment (SFSW) of the EN AW 6082 aluminum alloy. The research aimed at the comparative analysis of the results obtained to the FSW and SFSW welding of the EN AW 6082 aluminum alloy, using the same tool type and base material thickness. The obtained results will be a starting point for outlining of the future experimental research programs of friction stir processing in air and in liquid environment of EN AW 6082 alloy, which will be carried out within the ongoing Nucleu PN 23 37 01 02 project.

Abstract: Currently, worldwide priority industrial fields have a continuous and rapid development from a scientific and technological point of view. This fact determines the development of new manufacturing processes, new materials and technologies, the reconfiguration and modernization of important industrial sectors, in order to adapt to the current high performance and quality requirements. At the same time, new processes for joining and processing metallic materials, as well as methods and techniques for their application, current at the international level, were developed. Thus, friction stir welding (FSW) is a material joining process of international interest in top research centers and at the industrial level. One application variant of this process is FSW welding in a liquid working environment (Submerged Friction Stir Welding - SFSW), research on the application possibilities for different types of materials being in continuous development. The paper presents comparative results of ISIM Timisoara regarding the FSW and SFSW welding of EN AW 7075 aluminum alloy 5mm thick, using the same type of welding tool. These results are useful in the experimental researches of friction stir processing in air (FSP) and in liquid environment (SFSP) of aluminum alloy EN AW7075, which will be carried out in the Nucleu project PN 23 37 01 02 underway at ISIM Timisoara.

Abstract: The friction stir welding (FSW) process was developed by the Welding Institute (TWI) in 1991. The idea started from the need to use materials with high strength and low density in the aerospace and automotive industries to increase their performance. The FSW process enables the welding of dissimilar metals such as Al/Mg, Al/Cu, Cu/Mg, etc., without melting the base metal and avoiding the defects seen during fusion welding. FSW joining leads to a core and heat-affected zones with a behaviour different from that of the base metal. The behaviour of these zones influences the global behaviour of the welded structure and for this reason it is important to define the local behaviour. The present study focuses on identifying the local behaviour of a weld using numerical simulation. For this, the global model of the welded joint is created, by defining the specific areas of friction welding with rotating active element (the base material-MB; the thermally affected zone from the retreating side of tool- HAZ RS; the thermo-mechanically affected zone from the retreating side of the tool - TMAZ RS; the core of the weld - N, the thermo-mechanically affected zone from the advancing side of the tool - TMAZ AS; the thermally affected zone from the advancing side of the tool - HAZ AS) and the simulation of the tensile test is carried out. The local behaviour obtained after the simulation is compared with the behaviour obtained experimentally in the specialized literature. Next, the correlation of Abaqus and Matlab programs is presented to analyze and compare experimental data from the literature with those obtained from the simulation by applying the reverse method. This consists of introducing experimentally identified parameters into the numerical simulation, determining an eloquent comparison criterion, defining the error function and minimizing it. The inverse method presented in this paper opens new opportunities for its use in much more in-depth analyses.

Abstract: Improving diamond growth to achieve high-quality materials for applications like optics and quantum detectors is a key objective. Leveraging machine learning, especially with its challenges such as complex, time-dependent data features and the sheer data volume per growth cycle, presents a promising solution. The extraction of accurate spatial features from images for real-time diamond growth monitoring is challenging due to data's complex and sparse nature. This paper evaluates various feature extraction methods in diamond growth, introducing a novel deep learning approach for precise geometric feature segmentation. It utilizes a human-in-the-loop system for efficient data annotation, significantly cutting down labeling time and costs. Our approach, using the DeeplabV3plus model, showcases high efficiency in feature classification, with accuracies up to 96.31% for pocket holders, 98.60% for diamond tops, and 91.64% for sides, demonstrating deep learning's potential in handling complex dataset features effectively.

Abstract: Hierarchical honeycombs with sandwich cell walls are classified as advanced honeycomb structures with enhanced mass-specific mechanical properties. In this paper, we present a hierarchical honeycomb composed of corrugated sandwich cell walls and investigate its effective elastic response in terms of the nine elastic constants of orthotropic materials. An analytical model is employed to predict the elastic constants, which has been previously utilized for similar honeycombs with sandwich walls of solid homogenous cores. Numerical predictions were obtained through a finite element-based homogenization technique and used to validate the analytical model predictions for a range of design parameters. Results indicate that the optimal design increases the in-plane stiffness by up to 350%, while a reduction of 20% occurs for the out-of-plane shear stiffness.