Materials Science Forum Vol. 1150

Abstract: This study evaluates the fusion of 6061 Aluminum alloy with Mild Steel — materials known for their superior technical attributes yet distinct mechanical and physical properties — through Metal Inert Gas Arc Welding (MIG). The objective is to create a joint of dissimilar materials that boasts a robust strength-to-weight ratio, suitable for sectors like automotive, aviation, aerospace, and marine. A significant hurdle in this welding technique is preventing the creation of fragile intermetallic compounds (IMCs) that could compromise the joint's integrity and depth of penetration. The research outlines a method for adjusting welding parameters and setups to curtail the IMC thickness at the interface of the mild steel, which was observed to be between 2-6 μm in the conducted tests. The findings suggest that the MIG welding-brazing method can successfully form joints of dissimilar materials with mechanical strengths on par with other welding techniques. Additionally, variations in the maximum IMC layer thickness were noted with changes in welding parameters such as voltage, wire feed rate, gas shielding, and the configuration of the mild steel, as evidenced by the experiments. Notably, an increase in wire feed rate led to a more substantial IMC layer due to the higher heat input and prolonged arc time, facilitating more intense diffusion and interaction between the aluminum and steel. An exponential increase in the IMC layer thickness was recorded on the mild steel side with rising voltage, whereas the aluminum side's IMC layer thickness remained consistent.

Abstract: This paper discusses the wear behavior of self-mated AISI52100 bearing steel lubricated by polyol ester containing additives of bacterial cellulose particles. The wear properties are compared to those of surfaces lubricated by the base fluid without the additive. The sliding tests were conducted using a pin-on-disk reciprocating tribometer at room temperature. The results indicate that after a sliding distance of 72 meters, the friction coefficient was relatively similar for both lubricant conditions. However, the wear of the material was significantly reduced with the presence of cellulose particles in the lubricant, improving it by almost 100%. Observation of the worn area of the pin indicates the formation of a tribofilm on the contact interface facilitated by the cellulose particles. EDX analysis revealed that the film comprises oxygen and carbon-rich elements. It seems that the tribo-layer formed by a tribo-chemical reaction during sliding has acted as a protective barrier, preventing surface material ploughing and reducing wear on the tribo-pair.

Abstract: Activated carbon plays an important role in improving the performance of Electric Double Layer Capacitors (EDLCs), and research has been conducted on controlling the pore structure of activated carbon, which has a very high specific surface area. However, breakthroughs in electrodes have been difficult to achieve by pore control alone. In this study, specific capacitance, internal resistance, energy density, and power density of coin cell electrodes were calculated from electrochemical measurements using basic activated carbon, and their characteristics were evaluated. As the results, it showed the performance increased. This is thought to have been influenced by the increase in hydrophilicity due to the basicity of the activated carbon surface. It can be concluded that the increase in hydrophilicity is related to the increase in surface area contributing to the adsorption of ions due to improved electrolyte leakage during the charging and discharging process, resulting in the observed improvement in performance.

Abstract: As a high-temperature superconducting material, YBCO superconducting tape has great potential for use in power transmission. However, the critical current density (J_c) in superconducting cables is currently too low for practical applications. The longitudinal magnetic field effect is an effective way to improve the J_c of superconducting materials. J_c in the longitudinal magnetic field (LMF) is greater than J_c in the transverse magnetic field (TMF). On the other hand, the anisotropy of the upper critical field (B_c2) refers to the phenomenon that the B_c2 of superconducting materials changes when the direction of the external magnetic field changes from the ab plane to the c-axis of the YBCO superconducting tape. The objective of this study was to investigate the effects of the longitudinal magnetic field effect and the anisotropy of B_c2 on the J_c characteristics of YBCO superconducting tape. Two cases were set up in this study. In case 1, the direction of the external magnetic field is always parallel to the surface of the YBCO superconducting tape, while in case 2, the direction of the external magnetic field changes from parallel to the surface to perpendicular to the surface. By changing the experimental conditions, J_c was measured at different magnetic field strengths (B), different magnetic field directions (ϕ) and different temperatures (T). The influence of each variable on J_c in the two cases was clarified. Through the experimental results and discussions, the following conclusions were drawn: In comparison to the transverse magnetic field, J_c is increased by up to 30 times in the longitudinal magnetic field. In case 1, the main factor affecting J_c is the LMF effect. In the high-temperature region (80 K), the LMF effect on J_c is significantly greater than in the low-temperature region (40 K). In case 2, as the angle (ϕ) between the direction of the applied magnetic field and the current increases, B_c2 in case 2 gradually decreases, while B_c2 in case 1 remains unchanged, which is the reason for the more significant change in J_c in case 2. Compared with case 1, in case 2, in the low-temperature region (40 K), the LMF effect is the main factor affecting J_c. As T increases, the LMF effect on J_c gradually decreases, and the anisotropy of B_c2 gradually increases. In the high-temperature region (80 K), the anisotropy of B_c2 becomes the main factor affecting J_c.

Abstract: Silicon carbide (SiC) ceramics have excellent properties such as high thermal conductivity, heat resistance and high hardness. However, their low strengths due to the low fracture toughness make it difficult to produce SiC ceramics with large size and complicated shapes. The purpose of this study is to fabricate SiC/Si₃N₄ composite materials (SiC > Si₃N₄) reinforced by β-Si₃N₄ rod-like crystals (whiskers) in order to improve the mechanical properties of SiC ceramics. In this work, following two methods for fabricating SiC/Si₃N₄ composites have been developed. Method Ⅰ: porous β-Si₃N₄ with porosity more than 50 % was infiltrated by phenolic resin, heat-treated in N₂ atmosphere to convert phenolic resin to carbon, and finally infiltrated by molten Si into the porous β-Si₃N₄-carbon composites (reaction bonding). Method Ⅱ: hot-pressing the powder mixture of SiC and the β-Si₃N₄ whiskers with sintering additive. The microstructures and mechanical properties of SiC/Si₃N₄ composites fabricated by two methods were investigated.

Abstract: Cement-based piezoelectric composites (PECs) consist of calcium aluminate cement (CAC) and lead zirconate titanate (PZT), each accounting for 50 vol.% that can be used for structural health monitoring (SHM) due to their excellent compatibility with cementitious structures. The presence of free water inside the specimen significantly affects the polarization difficulty and piezoelectricity of PEC. Four treatment methods include vacuum drying, ethanol dehydration, non-heat treatment (untreated), and heat treatment to reduce free water in specimens. Experimental results show that reducing the free water content of PEC specimens through vacuum drying, ethanol dehydration, and heat treatment during the manufacturing process can enhance PEC performance. The free water reduction effect of PEC specimens was most with the heat treatment, followed by ethanol dehydration, and least by vacuum drying. The specimen’s dielectric loss and relative permittivity before polarization decreased if heat treatment and ethanol dehydration were applied. Heat-treated specimens provide optimal relative permittivity and piezoelectric strain constant after polarization. For the piezoelectric voltage constant, ethanol dehydration of the specimen is better than other treatments. The treatment method affects the resonance frequency value and the electromechanical coupling coefficient of the specimen. Water removal of specimens is not a suitable treatment method to increase the electromechanical coupling coefficient.