Hot corrosion behavior of Al2O3 laser clad plasma sprayed YSZ thermal barrier coatings (original) (raw)
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Materials & Design, 2014
Ceria-yttria stabilized zirconia (CYSZ) thermal barrier coatings (TBCs) were deposited by air plasma spraying on NiCoCrAlY-coated Inconel 738LC substrates. After that, the surface of plasma sprayed CYSZ TBCs were glazed using a pulsed Nd:YAG laser. The effects of laser glazing on hot corrosion resistance of the coatings were evaluated in presence of 45 wt%Na 2 SO 4 + 55 wt%V 2 O 5 corrosive molten salt at 1000°C. The results revealed that the hot corrosion resistance of plasma sprayed CYSZ TBCs were enhanced more than twofold by laser surface glazing due to reducing specific reactive area of the dense glazed surface layer and consequently, decreasing the reaction between molten salt and zirconia stabilizers.
Applied Surface Science, 2018
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 100 μm 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 300 μm. Hot corrosion behavior of YSZ, Gd2Zr2O7, YSZ/Gd2Zr2O7 TBC systems were exposed to 45 wt.% Na2SO4 and 55 wt.% V2O5 molten salt mixtures at 1000ᵒC 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.
Ceramics International, 2012
In the present work, the hot corrosion behavior of two types of multilayer plasma sprayed TBC were investigated and compared with functionally graded and conventional TBCs. These kinds of multilayer coatings consisted of nano/μ alumina as a top coat on YSZ layer, a metallic bond coat and a functionally graded intermediate layer deposited between YSZ and bond coat layers. All the layers were sprayed on the Ni-base super alloy substrate. The hot corrosion resistance of the plasma sprayed coatings was examined at 1050°C for 40 h, using a fused mixture of 45 wt% Na 2 SO 4 + 55wt%V 2 O 5. Before and after hot corrosion, the microstructure and phase analysis of the coating were studied using scanning electron microscope and X-ray diffractometer. The results showed that, the Al 2 O 3 top layer acted as a barrier against the infiltration of the molten salt into the YSZ layer during exposure to the molten salt mixture at the high temperature and the multilayer coatings of zirconia/alumina with the nanostructured alumina as a top coat showed higher hot corrosion resistance. Also, the failure mechanisms of the functionally graded coating and duplex TBC were investigated. The spallation occurred between the graded layer and the bond coat/top coat in functionally graded TBC and duplex TBC, respectively.
The Role of Nanostructured Al2O3 Layer in Reduction of Hot Corrosion Products in Normal YSZ Layer
YVO 4 crystals and monoclinic ZrO 2 are known as hot corrosion products that can considerably reduce the lifetime of thermal barrier coatings during service. The hot corrosion resistance of two types of air plasma sprayed thermal barrier coating systems was investigated: an Inconel 738/NiCrAlY/YSZ (yttria-stabilized zirconia) and an Inconel 738/NiCrAlY/YSZ/nano-Al 2 O 3 as an outer layer. Hot corrosion test was accomplished on the outer surface of coatings in molten salts (45% Na 2 SO 4 + 55% V 2 O 5) at 1000 ∘ C for 52 hour. It was found that nanostructured alumina as outer layer of YSZ/nano-Al 2 O 3 coating had significantly reduced the infiltration of molten salts into the YSZ layer and resulted in lower reaction of fused corrosive salts with YSZ, as the hot corrosion products had been substantially decreased in YSZ/nano-Al 2 O 3 coating in comparison with normal YSZ coating after hot corrosion process.
Comparison of hot corrosion behavior of nanostructured ScYSZ and YSZ thermal barrier coatings
Ceramics International, 2016
Hot corrosion behavior of nanostructured scandia (3.6 mol%) and yttria (0.4 mol%) stabilized zirconia (4ScYSZ) and yttria stabilized zirconia (4YSZ) were investigated. Thus, duplex TBCs (thermal barrier coatings), composed of a bond coat (NiCrAlY) and a top coat (4ScYSZ or 4YSZ), were deposited on the IN738LC Ni-based supperalloy by atmospheric plasma spraying (APS). Hot corrosion studies of plasma sprayed TBCs were conducted in 45 wt% Na 2 SO 4 + 55 wt% V 2 O 5 molten salt at 910 °C for different times. Based on the results, it was revealed that ScYSZ coating has more hot corrosion resistance than YSZ coatings. Moreover, the mechanisms of degradation of both TBCs under corrosion salt were suggested.
Plasma-sprayed YSZ coatings: Microstructural features and resistance to molten metals
Journal of Alloys and Compounds, 2009
Yttria Stabilized Zirconia (YSZ) coatings deposited by plasma spraying are widely used as thermal barriers onto metallic substrates, due to their attractive thermal properties and chemical inertia. In the present study, YSZ coatings were deposited onto steel substrates and their microstructure was investigated with X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The micro-and nano-scopic structural features were correlated to the performance of the coatings against corrosion by molten metals, which could simulate the industrial conditions of numerous applications. More precisely, in-scale porosity of the coatings and crystal parameters modifications were systematically examined and correlated to the corrosion behaviour in molten zinc, tin and aluminium baths for a 6 days testing period. The structural stability of the ceramic coating at high temperature, as well as the reactivity of the molten metal on the ceramic surface were preliminarily evaluated by thermogravimetric analysis and differential scanning calorimetry.
Key Engineering Materials, 2014
This paper presents laser surface modification process of plasma sprayed yttria stabilized zirconia (YSZ) thermal barrier coating (TBC) for enhanced hardness properties and low surface roughness. A 300W JK300HPS Nd: YAG laser was used to process YSZ TBC sample surface. The parameters selected for examination were laser power, pulse repetition frequency (PRF) and residence time. Micrographs of the TBC system were captured using EVO 15 Scanning Electron Microscope (SEM). Surface roughness was measured using 2-dimensional stylus profilometer. X-ray diffraction analysis (XRD) was conducted to measure phase crystallinity of the laser-modified coating surface. X-ray diffraction patterns were recorded in the 2θ range of 10 to 80° using Bruker D8 Advance system with 0.7Å wavelength from a copper source (~1.5Å). The laser modified surface exhibited higher crystallinity compared to the as-sprayed samples. The presence of tetragonal phase was detected in the as-sprayed and laser processed sa...
Materiali in Tehnologije, 2018
Thermal barrier coatings (TBCs) provide protection to minimize aggressive environmental conditions such as oxidation, corrosion and thermal shocks occurring at high temperatures. In this study, a CoNiCrAlY metallic-bond coat was deposited on an Inconel 718 superalloy substrate with a thickness about 100 μm using the atmospheric-plasma-spray (APS) method. The production of TBCs was accomplished by depositing Y2O3 partially stabilized zirconia (YSZ) and MgO-stabilized zirconia (MSZ) as two different ceramic top-coating materials, having the total thickness of 300 μm. The specimens were subjected to a metallographic investigation before the oxidation tests; their surface roughness, porosity, hardness and microstructural properties were investigated and then compared with the results obtained after the oxidation tests. The TBC systems were subjected to isothermal-oxidation tests at 900°C and 1000°C for (8, 24, 50 and 100) h. After the oxidation tests, XRD, SEM and EDX elemental analyses were carried out and the changes in the thickness and structure of the thermally grown oxide (TGO) layer were investigated. A remarkable change occurred between the top and the bond coat in the TBC systems depending on the increasing time and temperature. The TGO layer thickness showed an increase. At the interface, Al2O3 and other mixed-oxide layers occurred. Before and after the oxidation, XRD analyses showed that YSZ had a tetragonal phase and a bit of a monoclinic phase. The MSZ coating included tetragonal, monoclinic and cubic phases at the end of the oxidation. This phase transformation causes a large volume increase in an MSZ lattice. Due to this volume increase, MSZ coatings suffer more damage than YSZ coatings.
Journal of Rare Earths, 2014
Phase transformation of tetragonal ZrO 2 to monoclinic phase and also increment of bond coat oxidation kinetic (TGO thickening) can substantially restrict the life time of thermal barrier coating systems (TBCs). So, nanostructured and conventional Y 2 O 3 stabilized ZrO 2 coatings were evaluated in fused V 2 O 5 -Na 2 SO 4 salts during thermal exposure in air. Microstructural characterization showed lower hot corrosion products (monoclinic zirconia, YVO 4 crystals) formation and reduction of TGO thickness in thermal barrier coating system consisting of nanostructured Y 2 O 3 stabilized ZrO 2 (YSZ) top coat. It was found that inhomogeneities, pores and micro-cracks played a principal role in the molten salts infiltration into the YSZ coating during three steps of hot corrosion process. In the nanostructured YSZ coating with tri-model structure, nano zones which surrounded by fully molten parts could fill the aforementioned defects and could act as barrier for the oxygen and corrosive molten salts penetration into the TBC.