Examinando por Autor "Derazkola, Hamed Aghajani"

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    AA5754–Al2O3 nanocomposite prepared by friction stir processing: microstructural evolution and mechanical performance
    (Multidisciplinary Digital Publishing Institute (MDPI), 2024-04) Mohammed, Moustafa M.; Abdullah, Mahmoud E.; Rohim, M. Nafea M.; Kubit, Andrzej; Derazkola, Hamed Aghajani
    The utilization of Al2O3 nanopowder to reinforce AA5754 aluminum alloy through blind holes employing the friction stir processing (FSP) technique to produce an aluminum matrix nanocomposite is explored in this paper. Motivated by the necessity to enhance the strength and ductility of welded joints, the impacts of varying the tool rotational speed (rpm) and blind hole diameter on the microstructure and mechanical properties of the joints are investigated. Experimental characterization techniques including SEM, optical microscopy, microhardness, and tensile tests were employed to analyze the welded joints produced under different processing parameters (tool rotational speeds of 910, 1280, and 1700 rpm, and blind hole diameters of 0, 1, 1.5, and 2 mm). Comparative analyses were conducted against base metal properties and joints without reinforcement powder. It was found that the addition of nanopowder resulted in a decrease in the maximum generated heat during FSP, while also reducing the stir zone size compared to samples without nanopowder. Moreover, enhancements in both the strength and ductility of the joints were observed with the incorporation of Al2O3 nanoparticles. The optimal combination of welding conditions, observed at 1280 rpm rotational speed and 1.5 mm hole diameter, yielded a remarkable ultimate tensile strength of 567 MPa, accompanied by a hardness of 45 HV. These results underscore the potential of nano-Al2O3 reinforcement in significantly improving the mechanical properties of the produced nanocomposite, with implications for advancing the performance of welded structures in various engineering applications
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    Ítem
    Effect of warm forming process parameters on 42CrMo4 skew rolled bar mechanical properties and microstructure
    (Springer Science and Business Media Deutschland GmbH, 2024-04) Murillo Marrodán, Alberto; Bulzak, Tomasz; García Gil, Eduardo; Derazkola, Hamed Aghajani; Majerski, Krzysztof; Tomczak, Janusz; Pater, Zbigniew
    Skew rolling is a manufacturing process in which two or three rolls are used to reduce the diameter or modify the shape of a cylindrical workpiece, which is used to manufacture mechanical components such as shafts, rods or balls. Hot conditions are used to overcome limitations related to material ductility, residual stress and machine capacity. In this paper, the warm skew rolling (WSR) process of 42CrMo4 rods is modeled by the finite element method. The effects of forming parameters, namely initial temperature and roll rotational velocity, on the material strain rate, thermal properties, microstructure and hardness were analyzed. Simulation results were validated by experimental process data, while hardness tests and SEM-EBSD microscopy were used to assess mechanical properties and microstructure, respectively. The WSR resulting microstructure is different from the normalized ferritic–pearlitic initial one. The degree of spheroidization (DoS) of cementite increases with temperature. The maximum DoS of 86.5% occurs at the initial temperature of 750 °C, leading to the highest material softening. Rolling from lower temperatures favors grain fragmentation and the achievement of incomplete spheroidization, which, in combination with the highest proportion of high-angle boundaries, contributes to a higher hardness of the rods with respect to those rolled at higher temperatures. The highest reduction in hardness takes place at 750 °C and 30 rpm, leading to 209.4 HV1 (30.7% reduction) and 194.1 HV1 (35.7% reduction) in the near-surface and internal regions, respectively. The driving factor is the transformation of cementite precipitates into a spheroidal form characterized by the greatest degree of dispersion.
  • Miniatura
    Ítem
    Room temperature tribological properties of molybdenum-titanium-zirconium (TZM) in metal forming processes
    (Elsevier B.V., 2025-03) Derazkola, Hamed Aghajani; Pelcastre, Leonardo; García Gil, Eduardo; Jimbert Lacha, Pedro José; Hardell, Jens
    This study investigate the effects of temperature on the tribological properties of Titanium-zirconium-molybdenum (TZM). TZM alloy was subjected to sliding contact against AISI 430 steel counterparts at varying temperatures. The results shows, the coefficients of friction (COF) at interface were 0.77, 0.75, 0.71, and 0.69, in the case of 25 °C, 300 °C, 600 °C, and 900 °C test temperatures. The presence of MoO3 and Mo9O26 phases suggested the wear resistance and decreasing COF at high temperature. Temperature is a critical factor influencing material transfer between TZM and AISI 430 steel. The primary TZM wear mechanism at 25 °C involved scratching, surface deformation, and local cracks, while elevated temperatures near 900 °C intensified material adhesion phenomena with a surface shearing effect on the TZM surface after the trotest.