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    Characteristic and magnetic properties of Ni1-xZnxFe2O4 ferrites
    (Wiley-V C H Verlag Gmbh, 2016) Sahin, M.; Misirli, C.; Aras, M.
    Ferrites are magnetic ceramic materials which have additional metallic ion in ferrous oxide compounds. Ferrites are usually classified as soft or hard ferrites. In this study, characteristics and magnetic properties of magnetic materials having NiO1-xZnOxFe2O4 structure were investigated. Mechanical mixing of high purity NiO, ZnO and Fe2O3 powders were done to obtain homogenous NiO1-xZnOxFe2O4 powder mixture for x = 0.15, x = 0.50 and x = 0.85. These powder mixtures were pressed using hydraulic press machine and then subjected to sintering at same temperatures of 1000 degrees C for 1 hour. Obtained specimens were analyzed with scanning electron microscopy (SEM) imaging and energy dispersive X-ray fluorescence (EDXRF) technique for the investigation of structural analysis; magnetic properties were determined using vibrating sample magnetometer (VSM). However, effects of composition, specimens and Zn% element in magnetic materials after energy dispersive X-ray fluorescence on maximum magnetic moment (M-s) were analyzed using Taguchi orthogonal array design of experiments technique. The study indicates that Zn% element is the main process parameter that has the highest statistical influence on maximum magnetic moment. However, another parameter, composition, also has a significant effect on maximum magnetic moment. Then, Zn-content was found to have a significant influence on the magnetic properties of the system.
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    The Effects of Square and Circular Die-Orifices on the Performance of Combined Extrusion-Forging Process
    (Springer, 2012) Sezek, S.; Misirli, C.; Aksakal, B.; Can, Y.
    The upper bound (UBM) and finite element methods (FEM) both coupled with experiments have been conducted to analyze forming performance, load prediction, and pressure analyses in a combined extrusion-forging process using square and circular die orifices. The forming load was predicted by the UBM and the pressure distribution was analyzed by FEM and the performance of both the methods was compared to each other. The required extrusion forging force for square die orifice was found to be higher than in the circular die orifice. The highest pressures occurred on the edges of the square and circular orifices and the pressures increased with increasing friction and deformation. Although extrusion force predictions were found to be slightly higher in UBM than FEM, they were in good agreement with experimental results. The present analyses showed that UBM can be used in rapid prediction of required extrusion-forging loads and material flow, and FEM is more suitable to use in pressure distribution analysis for production of square and cylindrical parts.
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    HOMOGENISATION AND MICRO-ARC OXIDATION COATING PROCESS ON AZ91 Mg-ALLOY
    (Scibulcom Ltd, 2014) Misirli, C.
    The purpose of the study is to examine the effects of homogenisation and micro-arc oxidation coating (MAO) processes on mechanical and metallurgical properties of AZ91 magnesium alloy. 50 mm x 50 mm x 5 mm AZ91 Mg-alloy samples were prepared for this study. Half of the samples were homogenised in the furnace at 410 C for 5 h. Hence half of the homogenised and half of the non-homogenised samples were coated with the use of micro-arc oxidation (MAO) technique at fixed voltage degree to obtain 20, 60 and 120 pm coating thickness, respectively. The surface characteristics of the coated samples were examined by using scanning electron microscope. The layer compositions of the samples were examined by using X-ray diffraction and scanning electron microscope. Fatigue strength of the specimens was studied by fatigue tests. On the other hand, microhardness and surface roughness were investigated. Then, wear tests were carried out using 'ball-on-disc' type tribometer under dry sliding condition. It was found that homogenisation has a positive effect on the quality and the durability of the material.
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    PROPERTIES ANALYSIS OF THE SPRAY NOZZLES IN DRYING PLANT
    (Scibulcom Ltd, 2015) Misirli, C.; Sahin, M.; Yildirim, B.
    The process of evaporating liquid inside a material is called drying. In the technical sense, drying is a process in which humidity is released from the material by external intervention using various methods. In cacao drying experiments, cacao was pushed into the spray nozzles under high pressure of 180-200 bars. The heat of, the cacao reached 60 degrees C when it passed through the spray nozzles. However, the main purpose of this study is to examine the tribological properties of spray nozzles in cacao drying plant. Spray nozzles were made by using four different types of tool steels, which are 1.2379 cold work tool steel, 1.2550 hot work tool steel, 1.3343 high speed tool steel and 1.4140 correctional steel. Spray nozzles were processed according to the technical dimensions, were polished, and were brought to the desired hardness by thermal processes. Hardness of tool steels was measured in this way they were used in cacao spraying plant, and microstructure and surface roughness of specimens were examined. However, wear tests were performed for tribological characterisation under dry sliding condition without lubrication. Life-spans of the spray nozzles were determined after the experiment structures of tool steels were analysed. It was found that hardness level directly affected the coefficient of wear for the steels. Then, the tempering effect of the steels shows lower performance probably due to lower carbon and hardness levels.