Browsing by Author "Dogan, H"

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    Tribological properties of coated ASME 316L SS and comparison with a substrate
    Dogan, H; Findik, F; Morgül, Ö
    Coating is a process applied to surface of materials to have thermal insulation, hot corrosion, erosion and oxidation resistance. Due to their combination of high hardness and chemical stability thin titanium nitride and Tinalox PVD coatings have been successfully established in surface engineering. In the present study, wear and friction characteristics of TiN and Tinalox PVD coated ASME 316L stainless steel were investigated and compared with the substrate. To do this, friction and wear tests were done using Tribotester, S/N: 07-128 CSEM machine. Also, hardness variation was determined by means of CSEM Nano-Hardness Tester S/N: 4-113. It was seen that hardness was increased in TiN and Tinalox coated substrates, while friction coefficient and wear rate decreased.
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    Deposition of HA-GO on ASO modified Ti surface by EPD method and characterization of surface and biological properties of the coating
    Kirman, M; Dogan, H; Dikici, T
    In this study, the surfaces of titanium (grade 2) substrates were modified by different methods and then coated with a hydroxyapatite-graphene oxide (HA-GO) composite by electrophoretic deposition (EPD). The aim of the study is to improve the surface properties and increase the hydrophilicity of the surface of titanium by different surface treatments. The surface modification processes are as follows: sandblasting (S), acid etching (E), and finally anodic spark oxidation (ASO) on the etched surface. After the surface modification processes, the surface of titanium was coated with HA-GO suspensions (0, 2, 4, and 6 wt% GO) with a voltage value of 20 for 5 min by the EPD method. The surface morphology, elemental analysis, contact angle, phase composition, adhesion, biocompatibility, and bioactivity of the produced coatings were examined. Bioactivity analysis was performed in simulated body fluid (SBF) for 14 days. The MTT experiment was conducted with L929 (mouse fibroblast) cell cultures in accordance with the 70 % cell viability criterion. As a result of contact angle measurements, it was observed that all samples showed hydrophilic behavior due to the increased surface area after ASO treatment. The contact angle of the sanded surface was 71.03 degrees, whereas the contact angles of the ASO treatment and HA-GO coatings after the coating process were measured below 5 degrees. The bioactivity test results indicated that the surface modified with HA-GO (4 wt%) exhibited the best apatite nucleation outcome. As a result of the analysis with L929 cells, HA, HA-GO (2 wt%), HA-GO (4 wt%) composite coatings showed biocompatible behaviour with 102.17, 76.52, and 80.43 % cell viability, respectively. The best result in the adhesion test was reported for HAGO (4 wt%) coating with class 5B.
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    Life performance prediction of natural gas combined cycle power plant with intelligent algorithms
    Karaçor, M; Uysal, A; Mamur, H; Sen, G; Nil, M; Bilgin, MZ; Dogan, H; Sahin, C
    The efficient use of a system is enabled with the life performance estimations. Thus, the effective use of underground resources is realized especially natural gas. Based on this, life performance models were generated to aim of improving the efficient use of energy for a combined cycle power plant (CCPP) of 243 MW installed in Izmir, Turkey by using fuzzy logic (FL) and artificial neural network (ANN) in this study. Therefore, output power estimations were carried out. Depending on the developed models, an estimation of the energy that the CCPP can produce and provide to the interconnected system in the following years has been made. According to the obtained results, the error prediction rates of FL and ANN models were determined. It was found that while the energy relative error estimation value that can be produced between the years calculated in modeling using FL varies between 0.59% and 3.54%, this value was found to vary between 0.001% and 0.84% in modeling using ANN. This result shows that the ANN model is more suitable for the life performance estimations of such a nonlinear system.
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    Friction and wear behaviour of implanted AISI 316L SS and comparison with a substrate
    Dogan, H; Findik, F; Morgul, O
    Ion implantation creates alterations in surface composition or morphology of solids which yield to a modification of physical and especially mechanical properties;, such as hardness and modulus of elasticity. The aim of this study is to focus on the friction and wear behaviour of N-2 and Zr implanted and TiN coated 316L stainless steel and compare with a substrate, Particularly, stainless steels were of interest, because they often display a poor tribological behaviour, which can be improved when they are hardened by incorporating N-2, TiN and Zr and forming a hardened surface zone. The present implantations were shown to improve the friction coefficient as well as the wear resistance of the stainless steel surface. (C) 2002 Elsevier Science Ltd. All rights reserved.
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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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    Comparative study of wear mechanism of surface treated AISI 316L stainless steel
    Dogan, H; Findik, F; Oztarhan, A
    Coating is a technique employed for the surface of materials to have thermal insulation, hot corrosion and oxidation resistance. Ion implantation forms modifications in surface composition or morphology of solids which yield to a change of physical and especially mechanical properties such as hardness and modulus of elasticity. The objective of this investigation is to concentrate on the friction and wear behaviour of TiN, N-2 and Zr implanted and TiN and Tinalox PVD coated 316L stainless steel and compare with a substrate. Mainly stainless steels were of attraction, because they frequently demonstrate a poor tribological behaviour, which can be enhanced when they are hardened by incorporating N-2#, TiN Tinalox and Zr and forming a hardened surface zone.
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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.
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    Tribological studies of ZrO2-implanted on stainless steel substrate
    Dogan, H; Findik, F; Oztarhan, A
    The tribological properties such as surface hardness, friction and wear have been studied for AISI 316L stainless steel substrates which were co-ion implanted with zirconium and oxygen ions. It is found that the wear resistance for AISI 316L stainless steel substrates implanted with zirconium and oxygen ions increased quite a lot. It is concluded that the increase in surface microhardness and the decrease in friction coefficient of AISI 316L stainless steel substrates play an important role in improving the wear resistance, and the relationship between relative wear volume and microhardness is correlated for zirconium and oxygen co-ion implantation.