Browsing by Author "Turk, A"

Now showing 1 - 9 of 9
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    Isothermal oxidation behavior and kinetics of thermal barrier coatings produced by cold gas dynamic spray technique
    Karaoglanli, AC; Turk, A
    The cold gas dynamic spray (CGDS) method was employed to deposit the CoNiCrAIY bond coats of thermal barrier coating (TBC) system. The oxidation behavior of the coatings were investigated under isothermal oxidation at 1000 degrees C, 1100 degrees C and 1200 degrees C for 8, 24, 50 and 100 h. Recent studies on TBCs have concentrated on the CGDS process and its properties under working conditions. The motivation of this study is to investigate the oxidation behavior of TBCs produced using CGDS technique under service conditions and to determine the oxidation growth kinetics of thermally grown oxide (TGO). The results show that the isothermal degradation of coatings was considerably influenced by microstructure of coating, interfacial oxide growth rate, oxidation temperature and time. (C) 2016 Elsevier B.V. All rights reserved.
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    Investigation of in vitro behavior of plasma sprayed Ti, TiO2 and HA coatings on PEEK
    Sargin, F; Erdogan, G; Kanbur, K; Turk, A
    Orthopedic implants are one of the most reliable and widely used equipments to increase the quality of human life by enhancing or replacing damaged body parts and ensuring the problematic parts of the body to become operative after a short time period. Polyether ether ketone (PEEK) is a semi-crystal high-performance thermoplastic polymeric implant material which emerged as an alternative for metallic implants that used in orthopedic surgery. Although PEEK has some superior properties such as high melting point, superb wear resistance, excellent fatigue behavior, non-toxicity for bone tissue and elasticity modulus similar to human bone, PEEK has some disadvantages such as biologically inert behavior and low bioactivity. In this context, coating the implant surface to improve its osteointegration behavior is widely accepted. Coating PEEK polymers with bioactive materials such as Hydroxyapatite (HA) is among one of the solutions for this problem. In this study, in order to increase surface bioactivity of PEEK biomaterials, Titanium (Ti), Titanium dioxide (TiO2) and Hydroxyapatite (HA) powder combinations was coated on PEEK samples by using Atmospheric Plasma Spray (APS) method. Morphological and chemical characterization showed produced coatings are suitable for implantation process. Also in vitro tests performed in Simulated Body Fluid (SBF) revealed that HA, Ti + HA and TiO2 + HA coatings have bioactive property.
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    CUTTING-TOOL RECYCLING PROCESS WITH THE ZINC-MELT METHOD FOR OBTAINING THERMAL-SPRAY FEEDSTOCK POWDER (WC-Co)
    Altuncu, E; Ustel, F; Turk, A; Ozturk, S; Erdogan, G
    Various recycling processes for WC-Co cermets from cutting tools, such as chemical modification, thermal modification, the cold-stream method and the electrochemical method have been investigated and some of them are actually employed in industry. However, these conventional methods have many problems to be solved and they are not always established technologies. Therefore, a more economical and high-efficiency recycling procedure needs to be developed. In this study we investigated the applicability of the zinc-melt method (ZMM) for recycling WC-Co as a powder from cutting-tool scraps. It was proven that ZMM is an available technique for recovering the WC powder from the cutting tools. WC-Co powders are recovered and then spray dried, sintered and obtained as a feedstock material for thermal-spray coating processes.
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    Effect of shot peening on the oxidation behavior of thermal barrier coatings
    Karaoglanli, AC; Doleker, KM; Demirel, B; Turk, A; Varol, R
    A conventional thermal barrier coating (TBC) system is made up of a multilayered coating system that comprises a metallic bond coat including oxidation-resistant MCrAlY and a thermally insulating ceramic top coat including yttria stabilized zirconia (YSZ). In this study, in order to improve the oxidation behavior in conventionally produced TBC systems, shot peening process is applied for modification of surface layer structure of atmospheric plasma spray (APS) bond coats. The oxidation behavior of TBCs, produced by the APS process and subjected to shot peening, was investigated. Oxidation tests were performed under isothermal conditions at 1000 degrees C for different time periods. The coatings produced by the APS process include high porosity and oxide content due to atmospheric production conditions as well as exposure to very high temperature. In this study, the coatings, produced by the APS process, subsequently subjected to shot-peening, were compared with the ones which were not shot peened. Following the application of the shot peening process, a dense structure is obtained due to the plastic deformation effect in the metallic bond coating structure at a certain distance from the surface. To this end, the effects of the shot-peening on the high temperature oxidation behavior of the coatings are investigated and evaluated. (C) 2015 Elsevier B.V. All rights reserved.
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    Design and production of dye-synthesized solar cells with FTO/TiO2/ferroelectric dye/electrolyte/Pt/FTO architecture
    Ozkan, DC; Turk, A; Celik, E
    A new approach for the application of dye-synthesized solar cells is realized by using perovskite and single oxide micro/nanopowders. With respect to the literature, the desired energy efficiency of dye-synthesized solar cells is a priori established as perovskite and single oxide micro/nanopowders in a composite structure. In the present work, in order to produce dye-synthesized solar cells with FTO/TiO2/ferroelectric/dye/electrolyte/Pt/FTO architecture, their precursor solutions were prepared by using nitrate-based salts, solvents, and chelating agents. The obtained gel films were dried at 200 degrees C for 2 h and then annealed at temperatures of 500 degrees C and 850 degrees C for 2 h in the air. TiO2 and LaFeO3 powders were characterized through DTA-TGA, FTIR, XRD, SEM, and UV-Vis spectrometer machines. In line with the results obtained, dye-sensitized solar cell production, which can also be called ferroelectric photovoltaic cells with a combination of TiO2, was produced. It was found that the production of continuously applicable and sustainable dye-sensitive solar cells using LaFeO3 with together TiO2 powders can be useful as innovative and futuristic approaches.
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    A comparative study of oxidation kinetics and thermal cyclic performance of thermal barrier coatings (TBCs)
    Karaoglanli, AC; Grund, T; Turk, A; Lampke, T
    The present study was carried out to investigate the isothermal oxidation behavior, thermal cyclic performance and oxidation kinetics of thermal barrier coatings (TBCs) systems consisting of CoNiCrAlY metallic bondcoats produced by Atmospheric plasma spraying (APS) and high velocity oxy fuel spraying (HVOF) on Inconel 718 substrate. Yttria stabilized zirconia (YSZ) ceramic top coats was produced by APS process as for the insulation layer. The oxidation behavior of the coatings were investigated under isothermal oxidation conditions at 1000 degrees C, 1100 degrees C and 1200 degrees C for 8, 24, 50 and 100 h. The results of the experimental studies on the oxidation kinetics and microstructural evolution of APS and HVOF sprayed thermal barrier coatings (TBCs) are compared and discussed in the paper. The microstructural changes at the metallic/ceramic interface and growth behavior of the thermally grown oxide (TGO) layers during the isothermal oxidation and thermal cyclic tests were analyzed in detail.
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    Production and Characterization of Highly Conductive Aluminum Metal for Electric Motor Applications
    Yavas, A; Cilingir, C; Turk, A; Celik, E
    The aim of this research is to produce and develop high-conductive and non-magnetic Al-based materials used in industrial rotors to reduce rotor conductor losses and increase motor efficiency. To achieve this, ETIAL 7 Al metal was melted together with AlB2 and AlB12 inoculant materials at individually added proportions (ranging from approximately 0.025-0.300%) using an induction melting furnace. The removal of boron from Al metal was achieved by the interaction of boron with impurity elements at high temperatures and the formation of borides. Low-density metal borides precipitated into slag and high-density metal borides precipitated at the bottom of the molten metal in the induction furnace. As a result, the metal was rendered non-magnetic and its conductivity increased by removing impurity elements in the Al metal. After the casting process, the metal underwent heat treatment to obtain certain textures in the structure, which further enhanced its conductivity at desired directions. The elemental analysis, phase structure, chemical state, microstructural, electrical, and magnetic properties of the produced Al materials were characterized by using OEM, XRD, XPS, SEM-EDS, IA, and VSM. This study has successfully produced extra-high-conductivity and non-magnetic materials with an innovative approach, without changing the system, and in a cost-efficient manner compared to the current situation. These materials can be used to increase the efficiency of electric motors.
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    Influence of Inoculation and Texture on Enhancing Electrical Conductivity in Commercially Pure Aluminum for Squirrel-Cage Asynchronous Electrical Motors
    Cilingir, C; Turk, A; Yavas, A; Yigit, R; Celik, E
    This research focuses on manufacturing and applying highly conductive and non-magnetic aluminum-based materials in rotor construction to reduce conductor losses and increase motor efficiency. The process involves using an electric melting furnace to melt aluminum-boron (Al-B) master alloys at various rates along with 99.7% pure Al and impurities. During melting, the boron reacts with impurity elements in the Al, forming borides that are removed as slag. This interaction removes impurities, eliminating the magnetic properties of the Al and increasing its conductivity. The melted metal is then cast and subjected to heat treatment to achieve desired textures in their structure, further enhancing conductivity in specific directions. The outcome of this study is the production of extra-high-conductivity and non-magnetic materials through an innovative approach that does not require system changes or increase costs compared to current methods. The Al-3B master alloy and heat treatments significantly improve electrical conductivity in aluminum by enhancing metal orientation to (110) and eliminating structural defects. Heat treatments at 400 degrees C for 2 and 4 hours are most effective. These processes also reduce magnetic characteristics, resulting in improved rotor efficiencies in motor performance.
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    Effect of sintering on mechanical properties of cold sprayed thermal barrier coatings
    Karaoglanli, AC; Turk, A; Ozdemir, I
    In this study, thermal barrier coatings were deposited on nickel-based super-alloy with CoNiCrAlY bond and yttria partially stabilised zirconia top coats, using cold gas dynamic spraying and atmospheric plasma spraying techniques, respectively. High temperature oxidation behaviour and sintering effect on the mechanical properties of the coatings were studied. The main objective of this work is to explain the alteration in coating structure depending on temperature, and the mechanisms that lead to alterations in mechanical properties such as Young's modulus and hardness. Structural examination after oxidation revealed a decrease in porosity content and crack healing on ceramic top coatings resulting from sintering effect.