Developments in Processing of Ceramic Top Coats of EB-PVD Thermal Barrier Coatings

2007 ◽  
Vol 333 ◽  
pp. 137-146 ◽  
Author(s):  
Bilge Saruhan ◽  
Uwe Schulz ◽  
Marion Bartsch
Keyword(s):  
Thermal Conductivity ◽  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Morphological Changes ◽  
Turbine Blades ◽  
Young Modulus ◽  
Thermal Barrier ◽  
Cross Sectional ◽  
Barrier Coatings ◽  
The Cross

Partially Yttria Stabilized Zirconia (PYSZ) based Thermal Barrier Coatings (TBC) manufactured by EB-PVD process are a crucial part of a system, which protects the turbine blades situated at the high pressure sector of aero engines and stationary gas turbines under severe service conditions. These materials show a high strain tolerance relying on their unique coating morphology, which is represented by weakly bonded columns. The porosity present in ceramic top coats affects the thermal conductivity by reducing the cross sectional area through which the heat flows. The increase in thermal conductivity after heat-treatment relates to the alteration of the shape of the pores rather than the reduction of their surface-area at the cross section. The studies carried out by the authors demonstrate that the variation of the parameters during the EB-PVD processing of PYSZ based top-coats alters the columnar morphology of the coatings. Consequently, these morphological changes affect primarily the thermal conductivity and eventually the Young’ Modulus which are the key physical properties of this material group. New ceramic compositions covering zirconia coatings stabilized with alternative oxides, pyrochlores and hexaluminates are addressed. Failures occurring in ceramic top coats mark the lifetime of TBC system and therefore, it is necessary that their performance should go beyond that of the-state-of-the-art materials. This context summarizes the research and developments devoted to future generation ceramic top coats of EB-PVD TBCs.

scholarly journals Analysis of the energetic/environmental performances of gas turbine plant: Effect of thermal barrier coatings and mass of cooling air

2009 ◽  
Vol 13 (1) ◽  
pp. 147-164 ◽  
Author(s):  
Ion Ion ◽  
Anibal Portinha ◽  
Jorge Martins ◽  
Vasco Teixeira ◽  
Joaquim Carneiro
Keyword(s):  
Thermal Conductivity ◽  
Gas Turbine ◽  
Thermal Barrier Coatings ◽  
Turbine Blades ◽  
Heat Transfer Analysis ◽  
Thermal Barrier ◽  
Inlet Temperature ◽  
Barrier Coatings ◽  
Cooling Air Flow ◽  
Cooling Air

Zirconia stabilized with 8 wt.% Y2O3 is the most common material to be applied in thermal barrier coatings owing to its excellent properties: low thermal conductivity, high toughness and thermal expansion coefficient as ceramic material. Calculation has been made to evaluate the gains of thermal barrier coatings applied on gas turbine blades. The study considers a top ceramic coating Zirconia stabilized with 8 wt.% Y2O3 on a NiCoCrAlY bond coat and Inconel 738LC as substrate. For different thickness and different cooling air flow rates, a thermodynamic analysis has been performed and pollutants emissions (CO, NOx) have been estimated to analyze the effect of rising the gas inlet temperature. The effect of thickness and thermal conductivity of top coating and the mass flow rate of cooling air have been analyzed. The model for heat transfer analysis gives the temperature reduction through the wall blade for the considered conditions and the results presented in this contribution are restricted to a two considered limits: (1) maximum allowable temperature for top layer (1200?C) and (2) for blade material (1000?C). The model can be used to analyze other materials that support higher temperatures helping in the development of new materials for thermal barrier coatings.

scholarly journals Analytical and Experimental Study of Residual Stresses in Thermal Barrier Coatings Deposited on Gas Turbine Blades in Laboratory Dimensions by APS and HVOF Methods to Calculate the Optimal Thickness

2021 ◽  
Vol 3 (1) ◽  
pp. 63-67
Author(s):  
Esmaeil Poursaeidi ◽  
◽  
Farzam Montakhabi ◽  
Javad Rahimi ◽  
◽  
...  
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Analytical Model ◽  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Turbine Blades ◽  
Thermal Barrier ◽  
Inlet Temperature ◽  
Optimal Thickness ◽  
Barrier Coatings

The constant need to use gas turbines has led to the need to increase turbines' inlet temperature. When the temperature reaches a level higher than the material's tolerance, phenomena such as creep, changes in mechanical properties, oxidation, and corrosion occur at high speeds, which affects the life of the metal material. Nowadays, operation at high temperatures is made possible by proceedings such as cooling and thermal insulation by thermal barrier coatings (TBCs). The method of applying thermal barrier coatings on the turbine blade creates residual stresses. In this study, residual stresses in thermal barrier coatings applied by APS and HVOF methods are compared by Tsui–Clyne analytical model and XRD test. The analytical model results are in good agreement with the experimental results (between 2 and 8% error), and the HVOF spray method creates less residual stress than APS. In the end, an optimal thickness for the coating is calculated to minimize residual stress at the interface between the bond coat and top coat layers.

Application of an Industrial Sensor Coating System on a Rolls-Royce Jet Engine for Temperature Detection

2012 ◽  
Author(s):  
J. P. Feist ◽  
P. Y. Sollazzo ◽  
S. Berthier ◽  
B. Charnley ◽  
J. Wells
Keyword(s):  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Turbine Blades ◽  
Temperature Measurements ◽  
Thermal Barrier ◽  
Coating System ◽  
Excitation Light ◽  
Barrier Coatings ◽  
Jet Engine ◽  
Temperature Detection

Thermal barrier coatings are used to reduce the actual working temperature of the high pressure turbine blade metal surface and hence permit the engine to operate at higher more efficient temperatures. Sensor coatings are an adaptation of existing thermal barrier coatings to enhance their functionality, such that they not only protect engine components from the high temperature gas, but can also measure the material temperature accurately and determine the health of the coating e.g. ageing, erosion and corrosion. The sensing capability is introduced by embedding optically active materials into the thermal barrier coatings and by illuminating these coatings with excitation light phosphorescence can be observed. The phosphorescence carries temperature and structural information about the coating. Accurate temperature measurements in the engine hot section would eliminate some of the conservative margins which currently need to be imposed to permit safe operation. A 50K underestimation at high operating temperatures can lead to significant pre-mature failure of the protective coating and loss of integrity. Knowledge of the exact temperature could enable the adaptation of the most efficient coating strategies using the minimum amount of air. The integration of an on-line temperature detection system would enable the full potential of thermal barrier coatings to be realised due to improved accuracy in temperature measurement and early warning of degradation. This in turn will increase fuel efficiency and reduce CO2 emissions. Application: This paper describes the implementation of a sensor coating system on a Rolls-Royce jet engine. The system consists of three components: industrially manufactured robust coatings, advanced remote detection optics and improved control and readout software. The majority of coatings were based on yttria stabilized zirconia doped with Dy (dysprosium) and Eu (europium), although other coatings made of yttrium aluminium garnet were manufactured as well. Coatings were produced on a production line using atmospheric plasma spraying. Parallel tests at Didcot power station revealed survivability of specific coatings in excess of 4,500 effective operating hours. It is deduced that the capability of these coatings is in the range of normal maintenance schedules of industrial gas turbines of 24,000 hours or even longer. An advanced optical system was designed and manufactured permitting easy scanning of coated components and also the detection of phosphorescence on rotating turbine blades (13k RPM) at stand-off distances of up to 400mm. Successful temperature measurements were taken from the nozzle guide vanes (hot), the combustion chamber (noisy) and the rotating turbine blades (moving) and compared with thermocouple and pyrometer installations for validation purposes.

Fundamental Coating Development Study to Improve the Isothermal Oxidation Resistance and Thermal Cycle Durability of Thermal Barrier Coatings

2006 ◽  
Vol 522-523 ◽  
pp. 247-254 ◽  
Author(s):  
Taiji Torigoe ◽  
Hidetaka Oguma ◽  
Ikuo Okada ◽  
Guo Chun Xu ◽  
Kazuhisa Fujita ◽  
...  
Keyword(s):  
High Temperature ◽  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Turbine Blades ◽  
Atmospheric Plasma ◽  
Zirconia Ceramic ◽  
Thermal Barrier ◽  
Temperature Oxidation ◽  
Barrier Coatings ◽  
Oxidation Properties

Thermal barrier coatings(TBCs) are used in high temperature gas turbines to reduce the surface temperature of cooled metal parts such as turbine blades[1]. TBC consist of a bondcoat (e.g. MCrAlY where M is Co, Ni, CoNi, etc.) and a partially stabilized zirconia ceramic topcoat. Usually, the MCrAlY bondcoat is applied by LPPS (low pressure plasma spray) or HVOF(high velocity oxi-fuel spray). The topcoat is applied by APS (atmospheric plasma splay) or EB-PVD (electron beam-physical vapor deposition). High temperature oxidation properties, thermal barrier properties and durability of TBC are very important to increase the reliability in high temperature service. In this study, new TBC has been investigated. The new TBC consists of a two-layered bondcoat (LPPS-MCrAlY plus dense PVD overlay MCrAlY) and the EB-PVD type YSZ columnar structure topcoat. As a result of evaluation tests, it was confirmed that the new TBC had better oxidation properties and durability than a conventional TBC system.

Precision Temperature Detection Using a Phosphorescence Sensor Coating System on a Rolls-Royce Viper Engine

2012 ◽  
Author(s):  
J. P. Feist ◽  
P. Y. Sollazzo ◽  
S. Berthier ◽  
B. Charnley ◽  
J. Wells
Keyword(s):  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Turbine Blades ◽  
Yttrium Aluminium Garnet ◽  
Thermal Barrier ◽  
Successful Implementation ◽  
Coating System ◽  
Excitation Light ◽  
Barrier Coatings ◽  
Temperature Detection

By adapting existing thermal barrier coatings a sensor coating has been developed to enhance their functionality, such that they not only protect engine components from the high temperature gas, but can now also measure the material temperature accurately and the health of the coating e.g. ageing, erosion and corrosion. The sensing capability is introduced by embedding optically active materials into the thermal barrier coating and by illuminating these coatings with excitation light phosphorescence can be observed. The phosphorescence carries temperature and structural information about the coating. Knowledge of the exact temperature could enable the design of advanced cooling strategies in the most efficient way using a minimum amount of air. The integration of an on-line temperature detection system would enable the full potential of thermal barrier coatings to be realized due to improved accuracy in temperature measurement and early warning of degradation. This in turn will increase fuel efficiency and reduce CO2 emissions. Application: The work carried out included the successful implementation of a sensor coating system on a Rolls-Royce Viper engine. The system consists of three components: industrially-manufactured robust coatings, advanced remote detection optics and improved control and readout software. The majority of coatings were based on yttria stabilized zirconia doped with Dy, although other coatings made of yttrium aluminium garnet were manufactured as well. Coatings were produced on a production line using atmospheric plasma spraying. Parallel tests at Didcot power station revealed the durability of specific coatings in excess of 4,500 effective operating hours. It is expected that the capability of these coatings is in the range of normal maintenance schedules of industrial gas turbines of 24,000hrs or even longer. An optical energy transfer system was designed and developed permitting scanning of coated components and also the detection of phosphorescence on rotating turbine blades (13,000 RPM) at probe-to-target distances of up to 400mm. The online measurement system demonstrated precision (around ±5K) comparable to commercial thermocouples and has shown calibration accuracy of ±4K. Transient temperatures were tracked at maximum at 8Hz which is fast enough to follow a typical power generation gas turbine. Repeatable measurements were successfully taken from the nozzle guide vanes (hot), the combustion chamber (noisy) and the rotating turbine blades (moving) and compared with thermocouple and pyrometer installations.

Thermal Barrier Coating Validation Testing for Industrial Gas Turbine Combustion Hardware

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Jeffery Smith ◽  
John Scheibel ◽  
Daniel Classen ◽  
Scott Paschke ◽  
Shane Elbel ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Gas Turbine ◽  
Thermal Barrier Coatings ◽  
Turbine Blades ◽  
Current Status ◽  
Thermal Barrier ◽  
Engine Fuel ◽  
Coating System ◽  
Barrier Coatings ◽  
Sintering Resistance

As gas turbine (GT) temperatures have increased, thermal barrier coatings (TBCs) have become a critically important element in hot section component durability. Ceramic TBCs permit significantly increased gas temperatures, reduced cooling requirements, and improve engine fuel efficiency and reliability. TBCs are in use throughout the GT hot section with turbine blades, vanes, and combustion hardware, now being designed with TBCs or upgraded with TBCs during component refurbishment (Miller, 1987, “Current Status of Thermal Barrier Coatings,” Surf. Coat. Technol., 30(1), pp. 1–11; Clarke et al., 2012, “Thermal-Barrier Coatings for More Efficient Gas-Turbine Engines,” MRS Bull., 37(10), pp. 891–898). While the industry standard 6–9 wt. % yttria stabilized zirconia (7YSZ) has been the preferred ceramic composition for the past 30+ yr, efforts have been underway to develop improved TBCs (Stecura, 1986, “Optimization of the Ni–Cr–Al–Y/ZrO2–Y2O3 Thermal Barrier System,” Adv. Ceram. Mater., 1(1), pp. 68–76; Stecura, 1986, “Optimization of the Ni–Cr–Al–Y/ZrO2–Y2O3 Thermal Barrier System,” NASA Technical Memorandum No. 86905). The principal development goals have been to lower thermal conductivity, increase the sintering resistance, and have a more stable crystalline phase structure allowing to use above 1200 °C (2192 °F) (Levi, 2004, “Emerging Materials and Processes for Thermal Barrier Systems,” Curr. Opin. Solid State Mater. Sci., 8(1), pp. 77–91; Clarke, 2003, “Materials Selection Guidelines for Low Thermal Conductivity Thermal Barrier Coatings,” Surf. Coat. Technol., 163–164, pp. 67–74). National Aeronautics and Space Administration (NASA) has developed a series of advanced low conductivity, phase stable and sinter resistant TBC coatings utilizing multiple rare earth dopant oxides (Zhu and Miller, 2004, “Low Conductivity and Sintering-Resistant Thermal Barrier Coatings,” U.S. Patent No. 6,812,176 B1). One of the coating systems NASA developed is based on Ytterbia, Gadolinia, and Yttria additions to ZrO2 (YbGd-YSZ). This advanced low conductivity (low k) TBC is designed specifically for combustion hardware applications. In addition to lower thermal conductivity than 7YSZ, it has demonstrated thermal stability and sintering resistance to 1650 °C (3000 °F). The Electric Power Research Institute (EPRI) and cincinnati thermal spray (CTS) have teamed together in a joint program to commercialize the YbGd-YSZ TBC coating system for GT combustion hardware. The program consists of validation of coating properties, establishment of production coating specifications, and demonstration of coating performance through component engine testing of the YbGd-YSZ TBC coating system. Among the critical to quality coating characteristics that have been established are (a) coating microstructure, (b) TBC tensile bond strength, (c) erosion resistance, (d) thermal conductivity and sintering resistance, and (e) thermal cycle performance. This paper will discuss the coating property validation results comparing the YbGd-YSZ TBC to baseline production combustor coatings and the status of coating commercialization efforts currently underway.

Research on the Heat Insulation Performance of Advanced Thermal Barrier Coatings Based on Dense Vertical Cracked Structure

2019 ◽  
Author(s):  
Yun Long ◽  
Yuzhang Wang ◽  
Mengtian Zhao ◽  
Yiwu Weng
Keyword(s):  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Heat Insulation ◽  
Turbine Blades ◽  
Thermal Barrier ◽  
Reconstruction Method ◽  
Reconstruction Process ◽  
Barrier Coatings ◽  
Insulation Performance ◽  
Cracked Structure

Abstract The Thermal barrier coatings (TBCs) applied to gas turbine can effectively protect the metallic components from overheating. It makes contribution to raising turbine entry temperatures, which can improve the cycle thermal efficiency of turbine and prolong its service life. To understand the failure mechanism of TBCs and extend its lifetime, it is vital to prepare TBCs with excellent heat insulating performance. TBCs with dense vertical cracked structure is an essential kind of advanced thermal barrier coatings and has received great attention recently. However, most studies are based on laboratory-scale, since the complex coating preparation process makes it challenging to obtain the controllable microstructure distribution of the coating. Moreover, the thin slices of TBCs are difficult to get during the reconstruction process of the coating microstructure. Therefore, in this work, an optimized numerical reconstruction method of TBCs was applied to obtaining the TBCs with dense vertical cracked structure. The influences of the microstructural TBCs with different numbers of vertical cracks as well as different length and width of vertical cracks were herein discussed, together with the analysis by the developed numerical calculation program based on the lattice Boltzmann method (LBM). The results showed that the performance of heat insulation in dense vertical cracked coatings was improved as the characteristic network structure. Meanwhile, it indicated that the optimal heat insulation performance can get when the length and width of vertical cracks were around 125μm, 15μm respectively. The results can play a guiding role in choosing and designing the turbine blades for further development of gas turbines.

Degradation of Thermal-Barrier Coatings at Very High Temperatures

MRS Bulletin ◽  
1994 ◽  
Vol 19 (10) ◽  
pp. 46-49 ◽  
Author(s):  
F.H. Stott ◽  
D.J. de Wet ◽  
R. Taylor
Keyword(s):  
Thermal Expansion ◽  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Turbine Blades ◽  
Phase Changes ◽  
Nickel Base Superalloy ◽  
Thermal Barrier ◽  
Two Phase ◽  
Barrier Coatings ◽  
Thermal Expansion Coefficients

Thermal-barrier coatings are finding increasing use in engineering applications, particularly in gas turbines. Such coatings, consisting of ceramic insulating layers bonded to the superalloy substrate by oxidation-resistant alloy coatings, are deposited onto components to reduce heat flow through the cooled substrate and to limit operating temperature. They have been used effectively on static components such as combustor cans, flare heads, hot gas seal segments, fuel evaporators, and deflector plates, giving considerable improvements in component life. They have been used successfully on vane platforms. In recent years, the emphasis has shifted toward the development of coatings for high-risk areas, such as turbine blades.A ceramic thermal-barrier coating needs to be refractory and chemically inert, and to have low thermal conductivity. However, it also needs to possess a high thermal expansion coefficient of ~11 × 10−6 K−1, to match the nickel-base superalloy substrate. The latter specification has focused attention on ZrO2. However, ZrO2 is polymorphic and undergoes two phase changes, cubic to tetragonal at 2350°C and tetragonal to monoclinic at 1170°C. The latter transformation is accompanied by a 5% volume increase which means that ZrO2 has to be alloyed to stabilize one of the high-temperature phases. Early systems in the 1970s consisted of ZrO2 stabilized with MgO, but this has been shown to be a metastable system. Present-day commercial thermal-barrier coatings consist of a plasma-sprayed yttria- or magnesiastabilized zirconia layer on top of an M-Cr-Al-Y bond coat. The latter plays a very important role by helping to key the ceramic to the alloy substrate and to accommodate the mechanical strains arising because of differences in thermal expansion coefficients and elastic moduli between the ceramic and the substrate.

scholarly journals A Comparative Study on the Synthesis and Properties of Yttria Stabilized Zirconia (YSZ) and Lanthana Doped YSZ Plasma Sprayed Thermal Barrier Coatings

2013 ◽  
Author(s):  
S. T. Aruna ◽  
N. Balaji ◽  
B. Arul Paligan
Keyword(s):  
Thermal Conductivity ◽  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Operating Temperature ◽  
Yttria Stabilized Zirconia ◽  
Thermal Barrier ◽  
Spray Parameters ◽  
Stabilized Zirconia ◽  
Barrier Coatings ◽  
Plasma Sprayed

Ceramic thermal barrier coatings (TBCs) have been used for decades to extend the life of combustors and high temperature turbine stationary and rotating components to increase the operating temperature and in turn the performance of gas turbines or diesel engines can be increased. At present, thermal barrier coatings (TBCs) of Y2O3 partially stabilized ZrO2 (YSZ) films are widely used. In recent years ceramic compositions useful in thermal barrier coatings having reduced thermal conductivity are being explored to further increasing the operating temperature of gas turbines and improve the engine efficiency. In the present study, a comparison of the properties of state-of-the art 8wt% yttria stabilized zirconia (YSZ) and lanthana doped YSZ plasma sprayed coatings is presented. Plasma sprayable powders were prepared in the laboratory by a single step precipitation method and characterized. Both the powders had good flowability. These powders were plasma sprayed at identical critical plasma spray parameters. The coatings were characterized for phase, microstructure and thermal conductivity. Both the powders and coatings exhibited tetragonal form of zirconia and no traces of lanthana were observed. Both the coatings exhibited similar porosity levels. Microstructure of the coatings revealed porous coating with good adhesion of the bondcoat with the topcoat. Plasma sprayed 8wt% YSZ and lanthana doped YSZ exhibited thermal conductivity values of 0.88 and 0.67 W m−1 K−1 respectively which is lower than that reported in literature. This study shows that lanthana doping in YSZ helps in lowering the thermal conductivity and hence this coating may be a potential candidate for TBC application.

MICROCRACKS CHARACTERIZATION FOR THERMAL BARRIER COATINGS AT HIGH TEMPERATURE

2013 ◽  
Vol 20 (03n04) ◽  
pp. 1350035 ◽  
Author(s):  
J. J. HUA ◽  
W. WU ◽  
C. C. LIN ◽  
Y. ZENG ◽  
H. WANG ◽  
...  
Keyword(s):  
Failure Mechanism ◽  
Thermal Barrier Coatings ◽  
Gas Turbines ◽  
Turbine Blades ◽  
Heating System ◽  
Thermally Grown Oxide ◽  
Thermal Barrier ◽  
Service Temperature ◽  
Air Plasma ◽  
Barrier Coatings

Thermal barrier coatings (TBCs), used in gas turbine blades, are exposed to oxidation and thermal fatigue conditions. The characterization of TBCs was often performed in laboratory experiments, therefore, its detail failure mechanism is not quite obvious. For better understanding of the phenomenon, it is recommended to observe it under the condition simulating the real service conditions of gas turbines. In the present work, ZrO 2 coatings were prepared by air plasma spraying (APS). Scanning electron microscope (SEM), equipped with a heating system, was used to study the in situ microstructure change of TBCs at service temperature at which the aircraft is operated. The bond coat (BC) layer's thickening process and thermally grown oxide (TGO) generation along with the cracks growth are revealed. Moreover, the influence of the service temperature and holding time on the failure mechanism of TBCs is discussed. The crack healing produced during the coating re-melting reaction is observed, and it is the key factor to increase the thermal conductivity of the coating.

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