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Thesis (M.Sc.) Master Egypt - Japan University of Science and Technology (E-JUST) - School of Innovative Design Engineering - Materials Science and Engineering Department 2024

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Continuous research into innovative lightweight eutectic high entropy alloys has attracted the attention of numerous researchers This study investigates the thermophysical properties , thermal cyclability and conductivity of new lightweight eutectic high entropy alloys for usage as a phase change material in thermal energy storage applications The major requirements of Phase Change Materials (PCM) include high latent heat of fusion , long-term chemical stability , economic feasibility , no significant change in volume of the storage unit , and desired temperature range Four alloys were designed using the the thermodynamics parameters ; namely , AlMgZnCuSim , AlMgZCS AlMgZnisCuSis and AlMgZnsCusSis alloy with a balance between intermetallic and eutectics were produced to target energy storage as phase change materials The alloys were produced using two different subsequent melting processes First , Al-Cu-Si temary alloy with non-equiatomic composition was prepared using an (ARCAST 200 , ME , USA) electric arc melting furnace The raw materials were with purities greater than 99.9% and underwent three melting cycles to achieve homogeneity After are melting , the ingot , together with Zn and Mg with a purity level greater than 99.9%, was placed into a graphite crucible inside a stainless-steel reactor closed in an argon-protective atmosphere to prevent the presence of oxygen during the melting process The reactor was positioned within an electric muffle furnace and held at 750°C for 7 hours followed by a semisolid forging process conducted at 510°C , to investigate the behavior and phase transformations associated with this alloy The semisolid forging process demonstrated remarkable plasticity , significantly reducing sample thickness by 35% and 70%, respectively compared to the as-cast samples Also , with an increase in forging from the as-cast sample to a 70% reduction , the oxidation rate decreases during cyclic heating - cooling of the sample The alloy also exhibited an exceptional latent heat capacity of up to 168.9 kJ/kg ranking among the highest values reported for high-temperature metallic phase change materials The experimental and the theoretical computed specific heat capacity (Cp) of the alloy demonstrates a high degree of congruence with experimental data of other metallic thermal energy storage materials The oxidation kinetics showed an increasing pattern of weight change , adhering to a parabolic rate law The semisolid sample , which was 70% oxidized , displayed the lowest parabolic rate constant of 0.233 * 10 g/cm² after 500 minutes indicating a low oxidation rate , thus having good oxidation resistance Also , the thermal stability of the alloy has increased by applying more reduction

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