The cold gas dynamic spray (CGDS) method has been considered a promising technology to produce a metallic bond coat for thermal barrier coating (TBC) systems. In this study, CoNiCrAlY bond coats ...produced by CGDS method were coated with yttria-stabilized zirconia (YSZ) by electron beam physical vapor deposition (EB-PVD). TBCs were subjected to 50 wt % V2O5 and 50 wt % Na2SO4 molten hot corrosion salt combinations at 1000 °C. In the case of YSZ top coat on TBCs, the reaction between Na2SO4, V2O5, and Y2O3 salts generates YVO4 crystals, and these structures cause the transformation of tetragonal ZrO2 to monoclinic ZrO2. This situation occurs under operating conditions that lead to TBC failure. Hot corrosion behavior and the related failure mechanisms of TBC systems were investigated and discussed using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) analysis, and X-ray diffractometer (XRD).
Aluminide intermetallics with superior mechanical and thermal properties can be produced using various techniques. Laser-remelted coating surfaces provide lower porosity and superior adhesion to the ...substrate. In the present study, Fe and Al powders were sprayed on the 316L stainless steel substrate using high-velocity oxygen liquid fuel (HVOLF) technique. The produced composite coating was subjected to laser heat treatment for the remelting of the coating layer. HVOLF Fe/Al coating, the remelted coating and the substrate were exposed to isothermal oxidation tests at 950 °C for 5, 25, 50 and 100 h. Before and after the oxidation tests, the samples were characterized using x-ray diffraction, scanning electron microscopy (SEM) and SEM elemental mapping analysis. Fe and Al were alloyed with the substrate via laser melting, and thus, an alumina-forming surface layer was obtained. Besides, the surface hardness of the substrate was increased by the remelting process. After the oxidation tests, the obtained results showed that the laser-remelted coating exhibits better oxidation performance compared to the substrate material and HVOLF Fe/Al coating with the effect of the formation of the protective alumina oxide layer.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Thermal barrier coatings (TBCs) are extensively used to protect critical components such as aircraft turbines to provide thermal insulation at elevated temperatures. At high operating temperatures, ...damage mechanisms such as oxidation and hot corrosion result in spallation of TBC system. The spallation occurs due to the phase transformation during penetration of hot corrosion salts to top coat. YSZ is mainly used as top coat material for TBC systems. However, YSZ cannot be used in temperature higher than 1000 °C. More superior efficiency of gas turbine engines will demand a new generation materials for TBC systems. Nowadays, rare earth zirconates, Gd
2
Zr
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O
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, La
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Zr
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, YSZ/Gd
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Zr
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O
7
, and YSZ/La
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Zr
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O
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used as ceramic top coat materials in gas turbine engine components owing to their superior thermal isolation and hot corrosion resistance properties. In this study, hot corrosion mechanism, rare earth zirconates, and their properties as well as their hot corrosion behavior in TBCs were investigated based on literature studies.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Yttria Stabilized Zirconia (YSZ) is widely used as a traditional ceramic top coat material in gas turbine engine components. Nowadays, rare earth zirconates, as alternative materials to YSZ, are ...enhanced for use as top coat layer of TBC owing to their better thermal isolation properties. In the present study, metallic CoNiCrAlY bond coat powder was sprayed on Inconel 718 superalloy substrate by cold gas dynamic spray (CGDS) technique. After the deposition of bond coats, YSZ and Gd2Zr2O7 top coats were produced using EB-PVD process. TBCs were exposed to isothermal oxidation tests at 1100°C for 8, 24, 50 and 100h. Oxidation and growth behaviors of thermally grown oxide (TGO) layer were observed. TBC samples were investigated using scanning electron microscope (SEM), EDS elemental mapping and X-ray diffractometer (XRD) analysis before and after the oxidation tests. Oxidation performances of two different TBC systems were compared to each other according to the analysis results.
•Conventional (YSZ) and new generation (Gd2Zr2O7) TBC top coat materials were deposited on cold sprayed CoNiCrAlY bond coats using EB-PVD technique.•Oxidation tests were carried out on the TBC samples at 1100 °C in a time-dependent manner.•Although Gd2Zr2O7-TBC has better oxidation resistance with respect to TGO thickness, YSZ-TBC with higher fracture toughness will be more reliable in long service time.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In this study, it was aimed to determine the effect of laser re-melting on the oxidation behavior of high entropy alloys produced with electric current assisted sintering (ECAS). CoCrFeNi, ...CoCrFeNiAl0.5 and CoCrFeNiAl0.5Ti0.5 high entropy alloys (HEAs) were produced using ECAS. After the production of HEAs, the laser re-melting (LR) process was applied to the surface of sintered samples. Then, isothermal oxidation tests were carried out to HEAs at 1000 °C for 5, 25 and 75 h. Before and after the oxidation tests, the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) mapping analysis. The obtained results show that the LR process significantly improved the microstructural properties of ECAS-HEAs. More homogeneous microstructure, lower porosity and single-phase formations were observed in HEAs after LR. This has enabled a more stable microstructure compared to ECAS samples. After the oxidation tests, lower oxide layer thickness, lower oxide growth rates and lower inner oxide formation were obtained in laser re-melted HEAs. The presence of Al-rich phases enables the formation of alumina layer on the surface of HEAs. The best oxidation performance was obtained with laser re-melted CoCrFeNiAl0.5.
•CoCrFeNiAlxTiy HEAs were produced as simple and fast by the combination of sintering and laser re-melting techniques.•Laser re-melting enabling more homogeneous and dense surface have enhanced the oxidation performance of HEAs.•Mixing enthalpy values were found to be effective in phase formations after both sintering and laser re-melting.•CoCrFeNiAl0.5-LR exhibited better oxidation resistance due to having continuous Al2O3 layer.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Thermal barrier coating (TBC) systems are widely used to prolong the lifetime of hot section components in gas turbines. Oxidation degradation at high temperature is inevitable despite the use of TBC ...systems. In the current study, Yttria stabilized zirconia (YSZ)/CoNiCrAlY/Inconel 718 and La2Zr2O7 (LZO)/YSZ/CoNiCrAlY/Inconel 718 TBC systems were produced and exposed to high temperature oxidation tests. After the tests, a thermally grown oxide (TGO) layer formed at the interface between the bond and top coating due to the oxidation of bond coating. This layer has a critical importance for the lifetime of TBCs. The oxidation kinetics, rate constants, and activation energy values of both TBC systems were calculated using TGO thickness values. At the end of the oxidation tests, the double-layered LZO/YSZ TBC system exhibited better performance thanks to the lower oxygen permeability of LZO considering oxidation kinetics results and microstructural investigations. However, the formed TGO layer consisting of alumina and mixed oxides (MOs) led to crack formation at the interface. Besides, higher temperatures and increasing oxidation periods also degraded the integrity of top coatings due to the sintering effect. Chemical incompatibility did not affect the interface durability of the LZO/YSZ TBC system during the oxidation tests.
•TBCs were not spalled, yet included severe cracks around the TGO layer due to mixed oxides at 1200 °C for 100 h.•LZO/YSZ TBC exhibited lower TGO growth and had lower activation energy at the end of the oxidation tests.•Chemical incompatibility was not detected between YSZ and LZO.•YSZ has not exhibited phase transformation whereas LZO exhibited a bit depending on the initial deposition.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•TBCs of CoNiCrAlY, YSZ, Gd2Zr2O7 and YSZ/Gd2Zr2O7 coatings were deposited on the surface of Inconel 718 superalloy.•CGDS and EB-PVD techniques were used for deposition of the TBCs.•Hot corrosion ...behavior of TBCs produced by EB-PVD techniques were reported.•YSZ/Gd2Zr2O7 TBC double layer coating system showed better performance than YSZ and Gd2Zr2O7 coatings TBCs.
Thermal barrier coatings (TBCs) are mostly used in critical components of aircraft gas turbine engines. Hot corrosion is among the main deteriorating factors in TBCs which results from the effect of molten salt on the coating–gas interface. This type of corrosion is observed as a result of contamination accumulated during combustion processes. Fuels used in aviation industry generally contain impurities such as vanadium oxide (V2O5) and sodium sulfate (Na2SO4). These impurities damage turbines’ inlet at elevated temperatures because of chemical reaction. Yttria stabilized zirconia (YSZ) is a conventional top coating material for TBCs while Gd2Zr2O7 is a new promising top coating material for TBCs. In this study, CoNiCrAlY metallic bond coat was deposited on Inconel 718 nickel based superalloy substrate material with a thickness about 100μm using cold gas dynamic spray (CGDS) method. Production of TBCs were done with deposition of YSZ, Gd2Zr2O7, YSZ/Gd2Zr2O7 ceramic top coating materials using EB-PVD method, having a total thickness of 300μm. Hot corrosion behavior of YSZ, Gd2Zr2O7, YSZ/Gd2Zr2O7 TBC systems were exposed to 45wt.% Na2SO4 and 55wt.% V2O5 molten salt mixtures at 1000°C temperature. TBC samples were investigated and compared using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) analysis and X-ray diffractometer (XRD). The hot corrosion failure mechanisms of YSZ, Gd2Zr2O7 and YSZ/Gd2Zr2O7 TBCs in the molten salts were evaluated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Thermal barrier coatings (TBCs) are widely used to increase gas turbine efficiency and to prolong the lifetimes of superalloy substrates. Yttria (7–8%) stabilized zirconia (YSZ) is used as a state of ...the art TBC top coating material. In recent years, rare earth zirconates have drawn interest as top coating materials due to their high phase transformation temperature and low thermal conductivity. In the present research, CoNiCrAlY powders were sprayed on Inconel 718 superalloy substrates using high velocity oxy fuel (HVOF) deposition technique. YSZ, Gd2Zr2O7 (GZ) and YSZ/GZ top coats were then deposited on the resulting bond coat using EB-PVD technique. The produced TBCs were exposed to isothermal oxidation at 1100 °C for 4 different periods, and furnace thermal cyclic tests were conducted at 1150 °C. After thermal loadings, TGO (thermally grown oxide) growth behavior and crack surfaces of TBCs were evaluated. Samples were compared with each other using analysis techniques like scanning electron microscopy (SEM), energy dispersive sprectrum (EDS) elemental mapping and X-ray diffraction (XRD) before and after the oxidation tests. The results showed that double layered TBC system is more durable against high temperature degradations.
•YSZ, GZ and YSZ/GZ TBCs were successfully deposited on HVOF CoNiCrAlY bond coated Inconel 718 using EB-PVD technique.•YSZ/GZ TBC system exhibit the better performance at the end of the both tests, as GZ provided the low oxygen permeability and high sintering resistance contribute to YSZ.•At the end of thermal cycling tests, the chemical incompatibilities occurring in GZ and YSZ/GZ TBC systems did not affect the lifetime of TBCs.•Stresses in the TGO layer played a dominant role in damages of TBCs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Thermal barrier coatings (TBCs) commonly expose to oxidation, hot corrosion, and CaO-MgO-Al2O3-SiO2 (CMAS) attacks during the service condition. All of these attacks cause the spallation or ...delamination of TBCs from the bond coat. In this study, the effect of these attacks on YSZ and La2Zr2O7/YSZ TBC systems was investigated. YSZ and double layer La2Zr2O7/YSZ topcoats were deposited using electron beam physical technique (EB-PVD) on CoNiCrAlY bond coat produced by cold gas dynamic spray (CGDS) technique. CMAS tests at 1225 °C for 4, 8, 12, 16, 20, 24, 28, and 32 h and 5 h cyclic hot corrosion tests at 1000 °C were carried out on TBCs. Before and after the tests, TBCs were characterized using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), x-ray diffraction (XRD) and image analysis software program. At the end of the tests, the formed phases, microstructural changes, and general failure mechanisms were investigated in detail for each test. The general result shows that double-layered TBCs provide significant contributions and durability against high-temperature corrosive attacks of conventional YSZ TBC. In addition, in this study, hot corrosion damage mechanism and CMAS attack significantly damaged the column morphology of the EB-PVD method, reducing the thermal insulation properties and strain tolerance of TBCs. As a result of the tests, spallation and phase changes occurred in the damaged TBC systems.
•This work aims to investigate hot corrosion and CMAS behavior of conventional single and double layer TBC systems.•Changes of TGO layer, microstructural properties and chemical compatibilities of TBCs were comparatively investigated as functions of time and temperature.•Double layer La2Zr2O7/YSZ TBCs exhibit superior properties as compared to conventional single layered YSZ TBC.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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