Browsing by Author "Karamolla, M"

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    The effect of heat treatment on laser-welding performance of additive manufactured Ti6Al4V sheets
    Aydin, K; Karamolla, M; Karaagaç, I; Kaçal, A; Dogan, H
    In this study, the laser weldability of Ti6Al4V materials produced by the selective laser melting (SLM) method, which is an additive manufacturing method, and the effects of heat treatment applied to the welded material on the welding performance were investigated experimentally. Stress relief and heat treatment were applied to the materials joined by laser welding at 800 degrees C (below the alpha phase transformation temperature), 950 degrees C (between alpha and beta phase transformation temperature), and 1080 degrees C (above the beta phase transformation temperature). In addition, transverse and longitudinal welded joining techniques were also investigated to determine anisotropy in the produced parts. The mechanical properties in the laser-welded region were examined by hardness and tensile tests, and an optical microscope, scanning electron microscope (SEM), and X-ray diffraction (XRD) examined the changes in the microstructure. Grain growth was observed in the microstructure due to the increase in heat treatment temperature, and the tensile strength increased from 631.2 to 754.2 MPa in transverse bonding, while it increased from 648.1 to 761.9 MPa in longitudinal bonding. High hardness values due to Widmanstatten morphology were determined in the hardness test, especially after heat treatments at 950 and 1080 degrees C. It has been observed that the heat treatment increases the welding performance of the laser-welded material, and the best welding performance is obtained with a welding efficiency of 83.5% in the heat treatment at 1080 degrees C.
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    The Experimental Assessment of Deformation and Springback Behavior for Additive Manufactured Ti6Al4V
    Aydin, K; Karamolla, M; Karaagac, I; Kabakci, MO; Dogan, H
    In this study, heat treatment was applied to Ti6Al4V materials produced by the selective laser melting (SLM) method at 550 degrees C, 800 degrees C, 950 degrees C, and 1080 degrees C temperatures, and the effect of this process on microstructure and mechanical properties was also investigated. Moreover, the parts produced with the additive manufacturing technique can be exposed to many loads at the place of use. Therefore, to determine the resistance of the materials against bending, the V bending process was applied to the materials in 6-, 7.5-, and 9-degree dies. XRD and SEM investigated the microstructure and optical microscope changes, and the mechanical properties were examined by uniaxial tensile test and microhardness analysis. In the test samples, pore and unmelted powder particles due to production in the microstructure were observed, and it was observed that the grain sizes increased with the increase in the heat treatment temperature. It was observed that samples HT550, HT800, and HT950 were shaped without breaking in the bending process in the 6-degree die, and all the samples were broken in the experiments performed in the 7.5-and 9-degree die.
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    The effect of ambient temperature on electric power generation in natural gas combined cycle power plant-A case study
    Sen, G; Nil, M; Mamur, H; Dogan, H; Karamolla, M; Karaçor, M; Kuyucuoglu, F; Yörükeren, N; Bhuiyan, MRA
    Natural gas combined cycle power plants (CCPPs) are widely used to meet peak loads in electric energy production. Continuous monitoring of the output electrical power of CCPPs is a requirement for power performance. In this study, the role of ambient temperature change having the greatest effect on electric production is experimentally investigated for a natural gas CCPP. The plant has generated electricity for fourteen years and setup at 240 MW in Aliaga, Izmir, Turkey. Depending on the seasonal temperature changes, the study data were obtained from each gas turbine (GT), steam turbine (ST) and combined cycle blocks (CCBs) in the ambient temperature range of 8-23 degrees C. In electric energy production, an important decrease was in the GTs because of the temperature increase. This decrease indirectly affected the electric energy production of the STs. As a result, the efficiency of each GT, ST and CCB decreased, although the quantity of fuel consumed by the controllers in the plant was reduced. As a result of this data, it has been recommended and applied that additional precautions have been taken in the power plant to bring the air entering the combustion chamber to ideal conditions and necessary air cooling systems have been installed. (C) 2018 The Authors. Published by Elsevier Ltd.