Double-ceramic-layer thermal barrier coatings based on La2(Zr0.7Ce0.3)2O7/La2Ce2O7 deposited by electron beam-physical vapor deposition (original) (raw)
Related papers
… of Materials for …
Increasing the turbine hot gas inlet temperature is a potential way to improve the efficiency of the land base gas turbines. Since the nickel and cobalt based superalloy materials can not face temperatures higher than 950 o C, thermal barrier coatings (TBC) with better insulation properties are needed. For this reason thicker TBCs (> 500µm) are needed to improve the thermal insulation. However, the increased thickness of TBCs may lead to a reduced coating lifetime. In order to overcome this drawback, two modifications of the thick 8Y 2 O 3-ZrO 2 TBC's structure were studied. Within these two modifications the TBC coating surface layer was sealed by using phosphate impregnation or laser glazing. These procedures are expected to improve coating hot corrosion and thermal cycling resistance, due to the denser coating surface or with the controlled vertical crack network. In this study thermal diffusivity and specific heat analysis together with microstructural characterization were carried out considering the sintering effect and possible phase transformations at elevated temperatures, up to 1250 o C. Qualitative explanation of experimental results was taken account by modelling the effect of porosity on the thermal properties of TBC. Broad variations in microstructural and thermophysical properties were observed within modified coatings.
Advances in Materials Science and Engineering : An International Journal (MSEJ), 2016
Thermal Barrier Coatings (TBCs), routinely prepared from Ceramic based compositions (typically 8%Y2O3-ZrO2or 8YSZ) are being engineered to protect the metallic components from degradation in applications like gas turbines, jet and automotive engines. With a goal of finding improved TBC materials a wide variety of ceramics are being researched worldwide. Before physically preparing the TBCs of uncommon compositions in the laboratory, their suitability to perform can be predicted. Limited accessibility to detailed and realistic information on the influence of newer compositions (other than 8YSZ) on TBCs warrants methods to obtain this information.
Zirconia based pyrochlore thermal barrier coatings
IOP Conference Series: Materials Science and Engineering, 2019
Improvements in thermal barrier coatings (TBCs) technology, further than what is already in service to enable adequate protection to metallic components from higher (>1100 o C) operating temperatures requires newer developments in materials. Many research activities have been undertaken by scientists to seek alternatives after discovering the threshold of Yttriastabilized zirconia (YSZ) TBCs on standard aerospace materials at elevated temperatures. To increase the thermal performance of gas turbine engines, alternate TBC materials with better sintering resistance and lower thermal conductivity are required. One of the promising candidates for the TBCs is Pyrochlore-type rare earth zirconium oxides (Re 2 Zr 2 O 7 , Re = rare earth). Re 2 Zr 2 O 7 TBCs have higher phase stability, lower thermal conductivity, lower sintering rate, no phase transformation, and lower coefficient of thermal expansion at elevated temperatures when compared with YSZ. In this work, plasma spray powders of Lanthanum Zirconate (La 2 Zr 2 O 7) and Lanthanum Ceria Zirconate (La 2 (Zr 0.7 Ce 0.3) 2 O 7) were synthesized by the solid-state reaction method with the goal to develop pyrochlore oxide-based coatings with desired properties at high temperatures (>1200 o C), better than the YSZ TBCs: currently the most popular choice for TBCs. These TBCs are expected to increase gas turbine efficiencies while protecting the underlying metallic substrate at high operation temperatures. The evaluation of the synthesised TBCs has been carrying out by studying their performances at 1200 o C. Results of evaluation for phase composition by employing X-Ray Diffractometry (XRD), microstructure via Scanning electron Microscope (SEM) and chemical composition via Energy Dispersive spectroscopy (EDS) also have been included.
Surface & Coatings Technology, 2018
TBCs provide protection of superalloy substrates against harsh environments in gas turbine engines. Typical TBCs consist of two main coating layers called bond and top coat. Recently, zirconates have become attractive top coat materials as an alternative to yttria stabilized zirconia (YSZ) due to their superior thermal properties. Zirconates are deposited on YSZ layer to decrease the thermal conductivity and to minimize the oxygen penetration. Furthermore, their high melting point as well as phase stability and sintering properties render them promising materials for TBC applications. In this regard, YSZ and YSZ/La 2 Zr 2 O 7 top coats were deposited using EB-PVD technique on HVOF-CoNiCrAlY bond coated Inconel 718 superalloy, in the present research. TBCs were exposed to isothermal oxidation tests in high temperature furnace at 1000 °C with different time periods and also, they were subjected to furnace cycling tests at 1150 °C. After oxidation and thermal cycling tests, formation of thermally grown oxide (TGO) layers at the interface and crack surfaces were investigated according to analysis results. The results show that double layered TBC system exhibits better oxidation performance in terms of TGO growth and thermal cyclic lifetime compared to single layer TBC system.
Evaluation of oxidation and thermal cyclic behavior of YSZ, Gd2Zr2O7 and YSZ/Gd2Zr2O7 TBCs
Surface & Coatings Technology, 2019
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, Gd 2 Zr 2 O 7 (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.
Vacuum, 2020
Oxidation is an inevitable failure mechanism under the operating temperature in gas turbines. To avoid negative effects of oxidation, ceramic-based materials having low thermal conductivity and high stability should be used to hot section components. In accordance with this purpose, thermal barrier coatings (TBCs) are used in order to increase the lifetime of gas turbine engine components that have not reached to desired levels yet. Yttria stabilized zirconia (YSZ) has been used as a conventional top coat material in TBCs. Increased the turbine inlet temperatures (TIT) promote to researchers to try higher stable material such as rare earth zirconates. In this study, CoNiCrAlY metallic powders were sprayed using a new emerging technique as called cold gas dynamic spray (CGDS) on Inconel 718 substrates. Single layer YSZ, Gd 2 Zr 2 O 7 and double-layered YSZ/Gd 2 Zr 2 O 7 were deposited by electron beam physical vapor deposition (EB-PVD) technique as top coat materials. In high temperature furnace, both TBC samples were isothermally oxidized at 1000 � C under different time periods. TBCs were examined as microstructural before and after oxidation tests. Thermally grown oxide (TGO) layer forming at the interface during oxidation were investigated and compared for each TBC systems. Oxidation and TGO growth behaviors were discussed.
Coatings
Beneficial properties achieved by nanostructuring effects in materials have generated tremendous interests in applications in surface engineering, especially in thermal barrier coatings (TBC). Limitations in conventional TBC processing for gas turbines and aero-propulsion systems have been exposed during past decades when rapid progress was made in nano-structuring coating research and developments. The present work is a comprehensive review of the current state of progress in nanostructured TBC (Ntbc) in reference to its microstructure, damage progression, failure mechanisms and a wide range of properties. The review aims to address the comparative performance analysis between the nanostructured and conventional (microstructured) 6–8 wt.% yttrium stabilized zirconia (YSZ) TBC systems. Oxidation resistance and sintering behavior in two TBCs are considered as the central focus of discussion. A few schematics are used to represent major microstructural features and failure progression...
Bulletin of Materials Science, 2016
Thermal barrier coatings (TBCs) of yttria-stabilized zirconia (YSZ) of different thicknesses with an intermediate bond coat were deposited on C-103 Nb alloy using the air plasma spraying technique. The coatings were subjected to rapid infra-red (IR) heating (∼25 • Cs −1)upto∼1250 • C and exposed up to 100 s at this temperature with heat flux varying from 55 to 61 W cm −2. The TBCs were found to be stable and intact after the heat treatment. In contrast, at the same conditions, the uncoated C-103 alloy specimen showed extensive oxidation followed by weight loss due to spallation. A maximum temperature drop of ∼200 • C was observed on the opposite side of the coated alloy with 600 µm YSZ coat; as against negligible temperature drop in case of bare alloy specimen. The temperature drop was found to increase with the coating thickness of YSZ. The coatings before and after IR heating were investigated by scanning electron microscopy, X-ray diffraction, electron probe microanalysis, microhardness and residual stress measurements in order to understand the effect of thermal shock on the properties of the TBC. On account of these high-temperature properties, YSZ coating along with the bond coat is expected to find potential thermal barrier coating system on niobium alloys for supersonic vehicles.
Thermal cycle properties of plasma sprayed YSZ/Al2O3thermal barrier coatings
Surface Engineering, 2009
In the present study, yttria partially stabilised zirconia (YSZ)/Al 2 O 3 coatings, which are used for jet engines, gas turbines and diesel engines were coated with thermal barrier coatings to provide high thermal resistance, reduce the metal surface temperatures and increase component durability. The effect of alumina addition from 0 to 80 wt-% on the properties of plasma sprayed YSZ coatings was investigated. The coating comprised of YSZ-Al 2 O 3 (0, 20, 50 and 80 wt-%Al 2 O 3); NiCrAlY bond coat; and AISI 304L stainless steels substrates. Scanning electron microscopy was used to analyse the microstructures of the coated samples. Thermal shock tests were performed over the specimens, at 1000 and 1200uC for 5 min and then forced air quenching for 2 min. The microhardness was investigated depending on the alumina contents. Vickers hardness on cross-section of coatings was observed to increase with the increase in alumina mixing ratio. It was noticed that with increase in Al 2 O 3 content the thermal shock life of the specimens decreased.
Journal of the European Ceramic Society, 2007
Widely used in turbines for propulsion and power generation, thermal barrier coatings (TBCs) increase the efficiency of turbine engines by allowing them to work at higher temperatures, due to their thermal insulating properties. Typically TBC systems consist of a metallic bondcoat (BC) and a ceramic topcoat (TC). Previous research has revealed that ceramic TCs possess an amplitude-dependent mechanical behaviour and that they can be used as damping treatments, due to their good damping properties. The microstructure and the properties of ceramic TCs vary significantly depending on the employed deposition technique. This work investigates the differences in the mechanical behaviour of yttria-stabilised zirconia (YSZ with 8 wt% yttria) TC deposited by atmospheric plasma spraying (APS) and electron beam-physical vapour deposition (EB-PVD), by means of tests run with the amplitude dependent damping (ADD) test rig and of scanning electron microscopy (SEM) analysis.