Browsing by Author "Karaoglanli, AC"

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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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    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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    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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    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.