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    Chemical Composition Simplification of the Seydisehir (Konya, Turkey) Alumina Plant Waste
    (Springer, 2019) Kalsen, Tugba Selcen Atalay; Karadag, Hakan Burak; Eker, Yasin Ramazan; Kerti, Isil
    Red mud, a residue of alumina production from bauxite refining, contains oxides of valuable metals such as Fe, Al, Ti, Si, Na, Ca, etc. The presence of these numerous metal oxides does not allow introducing the highly basic raw red mud within any industrial process, which leads to its storage over a wide land area. In order to simplify the chemical composition of this waste, the effects of weak acid leaching (citric acid) and strong acid leaching (hydrochloric acid) are studied. The treatment efficiency is discussed based on scanning electron microscope and X-ray diffraction analysis of solid product and inductively coupled plasma spectrometry analysis of acidic solutions. The effects of temperature and acid concentration on metals dissolution are estimated by rough kinetic considerations which present results comparable to those in the literature. More than 50% of Al and 50% of Ca detected by inductively coupled plasma mass spectrometry were separated via the organic acid process, while during leaching with HCl whole Ca, Fe, and more than 60% Ti and 80% of Al similarly determined were recovered. This confirms that within the red mud, metals behave differently under several forms with different reactivity toward acidic medium. Therefore, an eventual combination of both acids can be an efficient way to prepare them ready and suitable for possible industrial applications.
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    The Effect of Ultrasonic Cleaning Upon Mechanical Properties of Metal Matrix Composites
    (Springer India, 2021) Aslan, Abdullah; Salur, Emin; Gunes, Aydin; Sahin, Omer Sinan; Karadag, Hakan Burak; Akdemir, Ahmet
    The aim of this study is to produce composite materials by recycling metallic chips, which are found in industry as a large amount of waste. In addition, it is aimed to investigate the effect of ultrasonic cleaning process as the consolidation behavior and mechanical properties of bulk material directly depend on the cleaning of waste metallic chips. In the present investigation, spheroidal graphite cast iron (GGG-40) was employed as reinforcement material in tin bronze (CuSn10) matrix system. GGG-40 and CuSn10 chips were cleaned by ultrasonic agitation in water for 20 and 40 min. Consolidation of the cleaned metallic chips was achieved with a hot press by applying 820 MPa pressure under 450 degrees C, and the cylindrical and prismatic metal matrix composite materials with different reinforcement ratios were successfully produced. Energy-dispersive X-ray and scanning electron microscopy analyses were carried out to determine the amount of the oxide removed from the surfaces of chips. The mechanical properties of the samples were determined by hardness, porosity, compression and three-point bending tests. According to the results of the analyses, it was found that CuSn10 surfaces were cleaned from 20%, 50% and GGG-40 surfaces from 35%, 39% oxides during 20- and 40-min cleaning time, respectively. In addition, the results of the mechanical tests revealed that increased ultrasonic cleaning time improves the consolidation quality of metallic chips and it provides successful covering of GGG-40 chips by the CuSn10 chips as a result of a better structural integrity. New machinery parts with high mechanical properties can be produced as a result of recycling of the metallic chips which are available as waste in industry by appropriate cleaning process and this situation makes this study more innovative, economical and environmentally friendly research.
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    Effect of Various Spheroidizing Methods on Microstructure-Mechanical Properties and Wear Performance of PM High-Carbon Steel
    (Springer India, 2022) Gokmese, Hakan; Karadag, Hakan Burak; Tasdogen, Hacer
    In high-carbon unalloyed steels produced by the powder metallurgy method, the effect of different spheroidizing heat treatments on microstructure, mechanical properties, and wear performance was studied. For this purpose, 1.2 wt% graphite powders were added to Fe powders, and a powder composition was formed. The prepared powder mixtures were pressed at room temperature under 850 MPa and then sintered at 1180 degrees C for 20 min. After sintering, sample phase compositions were determined by the XRD analysis. Then, three different spheroidizing heat treatments were applied. First, the conventional spheroidizing was used for 5-10-20-40 h at a constant temperature of 700 degrees C. Secondly, for 5-10-20-40 h, cyclical spheroidizing was involved in the temperature range of 700 degrees C and 740 degrees C. A third heat treatment (post-quenching spheroidizing), which represented the study's original aspect and was an alternative to these known spheroidizing methods, was applied. Fully austenitized work-pieces were quenched in water at room temperature. Consequently, the martensitic structure was formed. These samples were over-annealed for 5-10-20 h at 700 degrees C. Even after a short period, such as 5 h, homogeneous and fine spherical cementite was formed in the microstructure. Depending on the spherical cementite morphology and distribution, impact toughness and hardness values were evaluated. Besides, steels' wear characteristics were determined using the block-on disc device, and three-dimensional worn surface morphologies were examined with the profilometer device. With the scanning electron microscope (SEM), microstructures formed due to different heat treatments were displayed. Also, the fractured and worn surfaces of the samples were examined. It was determined that with the post-quenching spheroidizing treatment, which may be an alternative to known and widely used spheroidizing treatments, the desired microstructure and properties such as machinability and ductility could be achieved in a much shorter period.
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    Mechanical properties and microstructure of composites produced by recycling metal chips
    (Springer, 2018) Aslan, Abdullah; Gunes, Aydin; Salur, Emin; Sahin, Omer Sinan; Karadag, Hakan Burak; Akdemir, Ahmet
    In this study, the processing and mechanical properties of porous metal matrix composites (MMCs) composed of spheroidal cast iron chips (GGG40) and bronze chips (CuSn10) and formed by hot isostatic pressing were investigated. Bronze chips (CuSn10) were used as a matrix component, and spheroidal cast iron (GGG40) chips were used as a reinforcement component. The MMCs were produced with different CuSn10 contents (90wt%, 80wt%, 70wt%, and 60wt%). The hot isostatic pressing process was performed under three different pressures and temperatures. The produced MMCs were characterized using density tests, Brinell hardness tests, and compression tests. In addition, the consolidation mechanism was investigated by X-ray diffraction (XRD) analysis and scanning electron microscopy. The test results were compared with those for bulk CuSn10 and bulk GGG40. Mechanical tests results revealed that the metallic chips can be recycled by using hot pressing and that the mechanical properties of the produced MMCs were similar to those of bulk CuSn10. XRD and microscopy studies showed that no intermetallic compounds formed between the metallic chips. The results showed that the CuSn10 and GGG40 chips were consolidated by mechanical interlocking.
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    The Out-Of-Plane Compression Behavior of In Situ Ethylene Vinyl Acetate (EVA)-Foam-Filled Aluminum Honeycomb Sandwich Structures
    (Mdpi, 2023) Kalsen, Tugba Selcen Atalay; Karadag, Hakan Burak; Eker, Yasin Ramazan
    In this study, the mechanical behavior of aluminum honeycomb (AHC) sandwich structures filled with ethylene vinyl acetate copolymer (EVA) foam in situ under out-of-plane compression loading was investigated experimentally. Both non-filled and EVA-foam-filled sandwich specimens with three different AHC core cell sizes (5.20, 6.78, and 8.66 mm) were studied to correlate the foam-filling effect with a key structural parameter. The results showed that compression characteristic properties such as peak stress, plateau stress, and absorbed energy per unit volume of the sandwich structure increased with EVA foam filling. The structure showed high recoverability when the compression loading was removed due to the viscoelastic nature of EVA foam. Cored EVA sandwich with 8.66 mm AHC cell size was recovered at 44% of the original thickness. This result promises groundbreaking applications such as impact-resistant and self-healing structures. The microstructures were also observed using scanning electron microscopy (SEM) to investigate the failure and the recoverability mechanisms.