Browsing by Author "Uzun R.O."

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    The effect of the retrogression process on the wear behaviour of a 7075 aluminium alloy
    (Carl Hanser Verlag, 2012) Durmus H.; Uzun R.O.; Şahin S.; Yüksel N.
    Retrogression and re-aging (RRA) process are applied in an attempt to enhance mechanical properties and corrosion resistance of 7075 aluminium alloys. In this study, retrogression and re-aging process have been applied to a 7075 aluminium alloy at 170 °C for 5, 40, 80 min and wear resistance of RRA applied samples have been investigated by ball-on-disc wear test apparatus. Sliding distance has been chosen as 300 meters. Re-aging procedure has been carried out at 125 °C for 10, 20 and 30 hours. Minimum wear loss has been obtained by retrogression for 40 min and aging for 30 hours. © Carl Hanser Veriag, München.
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    Effect of mill type on morphology of AA6013 aluminium powder
    (Universidade Federal do Rio de Janeiro, 2016) Uzun R.O.; Durmuş H.
    In conventional recycling method, metal chips are cast after pressing and melting in electric arc furnace. Material loss occurs during the recycling from liquid metal due to the several reasons. Direct recycling method which produces the aluminium powder from aluminium chips using mechanical mill can be an alternative to conventional recycling method. Thus material and energy losses, and labour cost will be reduced by direct recycling method without melting. In this study, the particle morphology of powder direct recycled from AA6013 aluminium alloy chips with cryogenic, disc and ball type grinders is investigated. Mechanical milling resulted flaky and irregular shaped AA6013 particles. It was ascertained that the chips did not break sufficiently in despite of the long duration milling mechanisms by ball mill. Cryogenic mill provides the energy required for milling mechanisms to act. Disc mill has the highest impact energy was determined. Consequently, efficiency of ball mill is lower than the efficiency of cryogenic and disc type mills. Shape factors of powders produced with ball and cryogenic mills were found greater than that of the powder produced by disc mill. Disc mill has the most efficient and effective impact energy which produces the smaller particles per minute, was determined. © 2016 Universidade Federal do Rio de Janeiro. All rights reserved.
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    Thermodynamic Performance Evaluation of Concentrating Solar Collector with Supercritical Carbon Dioxide (sCO2) Base Nanofluids
    (Springer, 2020) Corumlu V.; Uzun R.O.; Ozturk M.
    The use of supercritical carbon dioxide as a working fluid is an important alternative to enable the use of parabolic collectors in the high-temperature applications field. In the present paper, the effects of carbon black nanoparticles dispersed in supercritical carbon dioxide (sCO2) base fluid on the energetic and exergetic performance of parabolic trough collectors are theoretically investigated. Thermal modeling and performance analyses are performed through the developed model in the Engineering Equation Solver software. To present operating conditions of the system, all working fluids are tested under a pressure of 80 bar at a mass flow rate of 1.1 kg/s. In these analyses, the fluid inlet temperature, ambient temperature, and nanofluid concentration are determined as the variable indicators. Up to approximately working fluid inlet temperature of 705 K, the exergy efficiencies of the concentrating collectors using the sCO2 nanofluids are higher than that of the concentrating collector using the sCO2 base fluid. Additionally, the exergy efficiency increases in the systems using nanofluids with 2% and 4% concentration ratio are between 0.34–6.96% and 0.49–11.44%, respectively, according to the system using base fluid. Besides, at the working fluid inlet temperature values greater than 705 K, the exergy efficiency of the collector of using the sCO2 working fluid is found higher than the collectors using the nanofluids. However, at the same working fluid inlet temperatures, the fluid outlet temperatures of the collectors with the sCO2 nanofluids are higher than the system with sCO2 working fluid. © 2020, King Fahd University of Petroleum & Minerals.
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    Improving the abrasion resistance of AISI 304L metallic biomaterial by microwave boriding
    (Inderscience Publishers, 2021) Arslan D.; Uzun R.O.
    Metallic materials are used as biomaterials thanks to their high mechanical properties. However, their low resistance to corrosion and abrasion reduces the biocompatibility of them. In this study, the abrasion resistance of AISI 304L metallic biomaterial was improved by pack-boriding with microwave hybrid heating. For this purpose, AISI 304L material was pack-borided by using EKABOR II powder for two, four and six hours in a microwave oven with a power of 2.9 kW and a frequency of 2.45 GHz at temperatures of 850°C, 900°C and 950°C. A boride layer with a thickness ranging between 12.1 μm–56.6 μm was obtained on the surface as a result of boriding. The specific wear rate of the AISI 304L material pack-borided for four hours at 950°C, which exhibits the highest wear resistance, has been determined as 1.04656 × 10–5 mm3/Nm. The abrasion resistance of AISI 304L metallic biomaterial was increased 28 times by microwave boriding. Copyright © 2021 Inderscience Enterprises Ltd.