Key Engineering Materials Vol. 1059

Abstract: In Al-5%Mg strip cast using a high-speed twin roll caster, surface cracks can occur and these cracks remain even after cold rolling. In order to eliminate cracks, cast strip was directly rolled in a semisolid state. Casting speed of the strip was 30 m/min. Cast semisolid strip was rolled at various reductions. Semisolid high-speed roll casting could be achieved using a copper roll and small roll load. Semisolid rolled strip was cold rolled down to 1 mm. The surface condition, microstructure and tensile strength of the cast and rolled strips were evaluated. Mechanical properties of the semisolid and cold rolled strip were compared to those of hot rolled and cold rolled strip, and those of only cold rolled strip.

Abstract: Semisolid forging of Al-10%Mg near the solidus line temperature was conducted. Al-10%Mg could be forged at a 50% reduction without cracks occurring. The casting structure of the metal changed to a plastic forming structure. Tensile stress, proof stress and elongation were also improved by semisolid forging. In particular, the elongation was remarkably improved. Improvement of proof stress was less than that of tensile strength or elongation. Fe was also added to Al-10%Mg to make a model alloy representing recycled Al-10%Mg, and semisolid forging was conducted. Elongation decreased, but tensile stress and proof stress increased slightly (by approximately 10%) with the addition of Fe. Semisolid forging was found to be useful for reducing the undesirable effects of the addition of Fe content on various mechanical properties of Al-10%Mg.

Abstract: For the fabrication of aluminum alloy foams, TiH₂ is used as a foaming agent. However, the detailed aspect of TiH₂ after fabrication is unclear. The objective is to reveal the aspect of TiH₂ by observing the inner surface of pores. The aluminum alloy foam was fabricated by adding TiH₂ into hypoeutectic Al-Si alloy in the semi-solid state and subsequent solidification. The stereo microscopic images and Scanning Electron Microscope images on the inner surface showed that many small angular particles were fixed on the surface. According to the element mapping on the gas-solid interface, it was revealed that those angular particles contained Ti inside. Based on the nominal particle size of the titanium hydride powder used in this study, these small particles are considered to be derived from titanium hydride. Additionally, hydrogen was released during Thermogravimetry-Differential Thermal Analysis and Mass Spectrometry. The results indicate that the titanium hydride was not completely decomposed during the foaming process.

Abstract: Organic light-emitting diode (OLED) technology is particularly favored for such devices due to its broad color spectrum, design flexibility, low power consumption, and suitability for miniaturization. While conventional OLED fabrication predominantly relies on vapor deposition, inkjet printing has recently emerged as a promising alternative for large-area OLED manufacturing because of its high material utilization and capability for scalable patterning. In this process, light-emitting materials are deposited in liquid form onto the substrate and subsequently dried to form a uniform thin film. However, several challenges remain. In particular, the solvent evaporation rate must be precisely controlled to minimize droplet shrinkage during drying, which can compromise film uniformity and adhesion. Moreover, external parameters such as temperature and humidity significantly influence the drying dynamics, and the choice of solvents and polymers plays a critical role in achieving the desired film quality. To address these challenges, we propose optimizing the ambient pressure to achieve improved curing morphology.

Abstract: In-plane switching (IPS) liquid crystal displays (LCDs) with low operating voltages and high contrast ratios can be achieved by optimizing the electrode structure. The optimized electrode structure may produce a strong transverse electric field within the IPS liquid crystal (LC) cell, resulting in a smaller on-state voltage (V_on). This work investigates the electro-optical properties of IPS-LC cells with different electrode configurations through simulation studies. Four configurations are proposed herein, including two flat-IPS and two wall-IPS LC cells with different geometric dimensions. The results reveal that reducing the geometric dimensions within similar structures leads to a lower V_on and a higher contrast ratio due to the stronger electric field generated by narrower electrodes and smaller gaps. The wall-IPS configuration exhibits a lower V_on and a higher contrast ratio compared to the flat-IPS configuration because the stronger electric field can more effectively reorient the LC molecules in the wall-IPS LC cell. The voltage-induced director orientations in both the flat-IPS and wall-IPS configurations confirm that the transverse electric field in the wall electrodes is stronger than that in the flat electrodes at equivalent voltages. Consequently, the LC molecules experience significant reorientation, which results in a reduced V_on and an increased contrast ratio in the wall-IPS LC cells. The wall IPS-LC cell with a low voltage and high contrast ratio has the potential for the development of high-performance advanced LC devices.

Abstract: Diamond-like carbon (DLC) films were deposited onto glass and silicon substrates utilizing Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) with an Argon/Acetylene gas mixture. Substrate biases were varied (0V, -55V, -100V) for both nitrogen-doped and undoped films. Optical band gap (Eg) decreased with increasing negative substrate bias specifically from 2.6 eV to 2.2 eV for nitrogen-doped DLC and from 1.6 eV to 1.3 eV for undoped DLC. Nitrogen doping generally results in films with wider band gaps compared to undoped films at equivalent biases to sp hybrid bond formation increasing bias reduces the band gap within each film type. I-V measurements revealed an increase in open-circuit voltage from approximately 0.648 V to a range of 0.678–0.698 V for cells incorporating nitrogen-doped DLC. This improvement is attributed to enhanced corrosion resistance and electrical conductivity suggesting the suitability of nitrogen-doped DLC for photovoltaic applications.

Abstract: This paper presents the simulation study of passivated backgated graphene field-effect transistors (GFETs) with different channel lengths using Victory Device tool by Silvaco TCAD. The passivated backgated GFETs were designed for radiation device applications. Six GFETs models with channel lengths ranging from 0.1 µm to 10 µm were analyzed to investigate the influence of variation in channel length on the conductivity of GFET. Nearly all devices with shorter channel lengths exhibit ambipolar characteristics with V-shaped curves, indicating the conductivity of holes and electrons at different bias conditions. Interestingly, GFETs with longer channels, specifically 3 µm, 5 µm, and 10 µm, exhibited unexpected W-shaped transfer characteristic curves, featuring multiple charge neutrality points (CNPs). This behavior is attributed to the non-uniform doping induced by charge interactions between the channel and the passivation layer. The central region of the channel may experience a higher doping effect due to impurity diffusion from the passivation material compared to the region near to the metal electrodes. However, the W-shaped curves of longer channel GFETs become less prominent when compared to smaller channel length devices. This suggests that high conductivity in shorter channel GFETs dominates the overall transfer curve performance. The analysis of output characteristics (I_D–V_D) at V_G = 10 V further supports the influence of channel length on device performance, with the shortest channel length (0.1 µm) recording the highest saturation current (I_SAT), followed closely by 0.6 µm, aligning with its strong ambipolar transfer characteristics. These findings highlight the importance of channel scaling in designing stable and reliable backgated GFETs for radiation applications.

Abstract: This study explores the use of Triply Periodic Minimal Surface (TPMS) structures, Schwarz Primitive, Diamond, and Gyroid, as liquid cooling heat sinks to enhance heat dissipation. Both uniform and graded-density designs were evaluated through numerical simulations and validated via metal additive manufacturing using AlSi10Mg alloy. The results show that increasing TPMS density improves thermal conductivity, while graded-density configurations offer a balanced performance between conduction and convection. Among the tested models, the graded-density Gyroid structure demonstrated the most efficient heat transfer, suggesting that TPMS-based heat sinks, particularly with density gradation, hold strong potential for next-generation thermal solutions in high heat flux environments.

Abstract: This study, based on the concept of a circular economy, utilizes cellulose from water bamboo shoot shell to synthesize a phosphorus-nitrogen flame retardant. This material is then used to improve the thermal properties of epoxy resin, resulting in a flame-retardant composite material with wider application potential. First, the husks were ground into powder, boiled, and dried. The powder was then reacted with phenyl phosphine (phenyl phosphinic acid), followed by the addition of triglycidyl isocyanurate (TGIC). Finally, epoxy resin and a hardener (DDM) were added to form the flame-retardant composite material. Thermogravimetric analysis (TGA) showed that the residual char rate increased from 15.3% to 25.5%, and the integrated programmed decomposition temperature (IPDT) increased from 659°C to 1058°C, demonstrating the composite's excellent thermal properties. The LOI value of pure epoxy resin was only 23%, but with the addition of a 40% flame retardant, the composite's LOI reached 26%. While epoxy resin does not achieve any UL-94 rating, the addition of a 40% flame retardant resulted in a V-0 rating with no dripping. This is because the phosphorus-based flame retardant forms a char layer upon high-temperature combustion, protecting the substrate from dripping. SEM was also used to observe the composite's surface morphology.