Advances in Thermal Barrier Coatings (TBCs): Materials, Fabrication, Corrosion and Applications

A special issue of Coatings (ISSN 2079-6412). This special issue belongs to the section "Ceramic Coatings and Engineering Technology".

Deadline for manuscript submissions: closed (31 July 2023) | Viewed by 15993

Special Issue Editors

Research Institute for Frontier Science, Beihang University (BUAA), No. 37 Xueyuan Road, Beijing 100191, China
Interests: thermal barrier coatings; environmental barrier coatings; coating preparation; high-temperature oxidation; hot corrosion

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Guest Editor
School of Materials and Metallurgy, Inner Mongolia University of Science and Technology, Baotou 014010, China
Interests: thermal barrier coatings; rare earth ceramic material

Special Issue Information

Dear Colleagues,

We would like to invite you to submit your research to this Special Issue, "Advances in Thermal Barrier Coatings (TBCs): Materials, Fabrication, Corrosion and Applications". As one of the key technologies for areo-engines, thermal barrier coatings (TBCs) have been applied to hot-section components of combustors, high-pressure turbine (HPT) blades, and HPT nozzles for decades. TBCs enable the areo-engines to operate at higher temperatures; therefore, efficiency can be improved, emissions can be reduced, and thrust can be increased. On the other hand, the higher operating temperature leads to some unavoidable limitations in TBC use, including accelerated sintering, phase transformation, and corrosion resulting from environmental deposits (CMAS) and molten salt. These cause the premature failure of TBCs. In the interest of improving the performance of TBCs and elongating their lifetime, we face a practical requirement for alternative TBC materials to be developed, with progress required in TBC fabrication science and technologies, TBC design strategies, corrosion protective methods and failure mechanisms.

This Special Issue will present the latest designs and developments in TBCs applied for areo-engines through original research papers and review articles from leading scientists and engineers across the world.

In particular, the topics of interest include, but are not limited to, the following:

  • Novel material candidates for TBC applications at ultra-high temperatures;
  • Fabrication science of TBCs by APS, EB-PVD, SPS and PS-PVD technologies;
  • Corrosion behaviour of TBCs in the presence of CMAS and/or molten salts;
  • Corrosion protective methods and corrosion resistance mechanisms of TBCs;
  • Thermal cycling performance and failure analysis of TBCs;
  • Long-life designs for TBCs.

Dr. Lei Guo
Dr. Jian He
Dr. Min Xie
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Coatings is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • thermal barrier coatings (TBCs)
  • thermal conductivity
  • toughness
  • CMAS corrosion
  • thermal cycling
  • long lifetime

Published Papers (12 papers)

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Research

Jump to: Review

19 pages, 17251 KiB  
Article
A Direct Laser Sintering Approach for the Electrophoretic Deposition Overlay of Yttria-Stabilized Zirconia on the Surface of a Thermal Barrier Coating System
by Maryam A. Ali Bash, Sami A. Ajeel, Ruqayah A. Abbas and Mohammed J. Kadhim
Coatings 2023, 13(10), 1695; https://doi.org/10.3390/coatings13101695 - 27 Sep 2023
Viewed by 739
Abstract
The laser sintering process and modification of yttria-stabilized zirconia (YSZ) coatings subjected to electrophoretic deposition (EPD) on YSZ air-plasma-sprayed (APS) thermal barrier coatings (TBCs) were investigated. A Ni-based superalloy was plasma-sprayed using yttria-stabilized zirconia (YSZ) to create a thermal barrier coating with a [...] Read more.
The laser sintering process and modification of yttria-stabilized zirconia (YSZ) coatings subjected to electrophoretic deposition (EPD) on YSZ air-plasma-sprayed (APS) thermal barrier coatings (TBCs) were investigated. A Ni-based superalloy was plasma-sprayed using yttria-stabilized zirconia (YSZ) to create a thermal barrier coating with a 400 μm thickness. The electrophoretic deposition (EPD) technique was used to deposit the nanopowder of YSZ on the surface of YSZ TBCs. In this study, a technology based on the direct sintering of a green EPD layer using a laser beam was employed. The best conditions for the deposition overlay of the YSZ coating using a DC current were obtained with an applied voltage of 40 V, deposition time of 5 min, and suspension concentration of 10 g/L. Iodine was added to the solutions as a stabilizing agent. To overcome the problems of high sintering temperatures, laser sintering was adopted as a new approach. The microstructures of all the specimens were studied using field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy (EDS) analysis. Surface roughness was investigated using atomic force microscopy (AFM) analysis and the central line average (CLA). The direct laser sintering (DLS) process for the EPD overlay on the surface of the TBCs caused a reduction in surface roughness and porosity, and improvements in the microstructural and mechanical properties of the surface coatings were observed. Full article
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15 pages, 6503 KiB  
Article
Effect of Pore Evolution on Thermal Diffusivity and Radiation Characteristics of Thermal Barrier Coatings after High-Temperature Exposures
by Zhou Xu, Shuheng Xu, Qiukun Zhang, Jianfei Xu and Dongdong Ye
Coatings 2023, 13(10), 1675; https://doi.org/10.3390/coatings13101675 - 25 Sep 2023
Viewed by 907
Abstract
Studying the impact of pores is crucial to enhancing the service performance of coatings, since they are a typical microstructure feature of thermal barrier coatings. In this paper, a coating prepared by the APS method was employed as the study object, and a [...] Read more.
Studying the impact of pores is crucial to enhancing the service performance of coatings, since they are a typical microstructure feature of thermal barrier coatings. In this paper, a coating prepared by the APS method was employed as the study object, and a scanning electron microscope and optical microscope were used to calculate the porosity after spraying or high-temperature exposures. Based on this, numerical calculations and simulations were used to evaluate the impacts of the pore structure and porosity on the heat conductivity and radiation characteristics of the coating. The results showed that, at high-temperature exposures, the horizontal pores inhibited thermal conductivity and radiation, but the column pores increased heat conductivity and radiation. The heat conductivity of the coating linearly decreased as the porosity increased, whereas the extinction coefficient increased, although at a slower and slower pace. When the porosity reached 15%, if the porosity was further increased, the thermal radiation energy did not change much, indicating that increasing the porosity would only block the heat radiation to a certain amount. This new and time-saving technique for materials research utilizing simulation and numerical computing may be utilized to optimize the microstructure of coatings to increase their service performance. Full article
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16 pages, 13498 KiB  
Article
CMAS Corrosion Behavior of Nanostructured YSZ and Gd-Yb-Y-Stabilized Zirconia Coatings
by Lanxin Zou, Minghao Gao, Na Xu, Jia Zhang and Xinchun Chang
Coatings 2023, 13(9), 1623; https://doi.org/10.3390/coatings13091623 - 15 Sep 2023
Cited by 1 | Viewed by 1027
Abstract
With the development of industry, the operating temperature of aero engines and gas turbines continues to increase; developing thermal barrier coatings (TBCs) with superior resistance to CaO-MgO-Al2O3-SiO2 (CMAS) corrosion has become a prominent research focus. In this study, [...] Read more.
With the development of industry, the operating temperature of aero engines and gas turbines continues to increase; developing thermal barrier coatings (TBCs) with superior resistance to CaO-MgO-Al2O3-SiO2 (CMAS) corrosion has become a prominent research focus. In this study, atmospheric plasma spraying (APS) was used to prepare yttria-stabilized zirconia (YSZ), nanostructured yttria-stabilized zirconia (n-YSZ), and Gd-Yb-Y-stabilized zirconia (GYYSZ) coatings. The effects of CMAS exposure on the microstructure, chemical composition, phase transition, and microhardness of the coatings were investigated. Comparative analysis revealed that both phase transition and exfoliation occurred in corroded YSZ and n-YSZ coatings, with n-YSZ exhibiting more pronounced changes. In contrast, GYYSZ coatings remained stable without phase transition and exhibited a smaller increase in microhardness (270 HV0.3). Consequently, doping Gd/Yb/Y elements into ZrO2 can improve the performance of TBCs. Full article
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59 pages, 9745 KiB  
Article
Principles of Machine Learning and Its Application to Thermal Barrier Coatings
by Yuan Liu, Kuiying Chen, Amarnath Kumar and Prakash Patnaik
Coatings 2023, 13(7), 1140; https://doi.org/10.3390/coatings13071140 - 23 Jun 2023
Cited by 2 | Viewed by 2013
Abstract
Artificial intelligence (AI), machine learning (ML) and deep learning (DL) along with big data (BD) management are currently viable approaches that can significantly help gas turbine components’ design and development. Optimizing microstructures of hot section components such as thermal barrier coatings (TBCs) to [...] Read more.
Artificial intelligence (AI), machine learning (ML) and deep learning (DL) along with big data (BD) management are currently viable approaches that can significantly help gas turbine components’ design and development. Optimizing microstructures of hot section components such as thermal barrier coatings (TBCs) to improve their durability has long been a challenging task in the gas turbine industry. In this paper, a literature review on ML principles and its various associated algorithms was presented first and then followed by its application to investigate thermal conductivity of TBCs. This combined approach can help better understand the physics behind thermal conductivity, and on the other hand, can also boost the design of low thermal conductivity of the TBCs system in terms of microstructure–property relationships. Several ML models and algorithms such as support vector regression (SVR), Gaussian process regression (GPR) and convolution neural network and regression algorithms were used via Python. A large volume of thermal conductivity data was compiled and extracted from the literature for TBCs using PlotDigitizer software and then used to test and validate ML models. It was found that the test data were strongly associated with five key factors as identifiers. The prediction of thermal conductivity was performed using three approaches: polynomial regression, neural network (NN) and gradient boosting regression (GBR). The results suggest that NN using the BR model and GBR have better prediction capability. Full article
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14 pages, 4848 KiB  
Article
CeO2 Protective Material against CMAS Attack for Thermal–Environmental Barrier Coating Applications
by Lei Guo, Yuanpeng Wang, Mingguang Liu, Yuan Gao and Fuxing Ye
Coatings 2023, 13(6), 1119; https://doi.org/10.3390/coatings13061119 - 18 Jun 2023
Cited by 2 | Viewed by 1340
Abstract
Calcium–magnesium–alumina–silicate (CMAS) attack is a crucial issue for thermal–environmental barrier coatings (T/EBCs) with the ever-increasing operating temperature of turbine engines. In this study, CeO2 has been demonstrated as a promising protective material for T/EBCs against CMAS attack. At 1300 °C, CeO2 [...] Read more.
Calcium–magnesium–alumina–silicate (CMAS) attack is a crucial issue for thermal–environmental barrier coatings (T/EBCs) with the ever-increasing operating temperature of turbine engines. In this study, CeO2 has been demonstrated as a promising protective material for T/EBCs against CMAS attack. At 1300 °C, CeO2 powder kept excellent phase and structural stability in molten CMAS; there were some CMAS constituents dissolved into the CeO2 lattice to form a solid solution. With higher CeO2 contents and longer duration time, more CeO2 solid solution particles were formed, which acted as the nucleating agent for CMAS crystallization. As a result, apatite, anorthite and wollastonite crystalline products were easily generated. At 1300 °C for 10 h, CeO2 pellets covered with CMAS powder had limited degradation, which was attributed to the rapid crystallization of molten CMAS due to the excellent nucleating agent effect of the precipitated CeO2 solid solution. Full article
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10 pages, 2808 KiB  
Article
Hot-Corrosion Behavior of Gd2O3–Yb2O3 Co-Doped YSZ Thermal Barrier Coatings in the Presence of V2O5 Molten Salt
by Yang Li, Yajuan She and Kai Liao
Coatings 2023, 13(5), 886; https://doi.org/10.3390/coatings13050886 - 8 May 2023
Cited by 2 | Viewed by 1026
Abstract
In this study, thermal barrier coatings (TBC) consisting of 3.5 mol% Yb2O3-stabilized ZrO2 co-doped with 1 mol% Gd2O3 and 1 mol% Yb2O3 (referred to as GdYb-YSZ) were fabricated by means of air [...] Read more.
In this study, thermal barrier coatings (TBC) consisting of 3.5 mol% Yb2O3-stabilized ZrO2 co-doped with 1 mol% Gd2O3 and 1 mol% Yb2O3 (referred to as GdYb-YSZ) were fabricated by means of air plasma spraying. The as-fabricated coatings exhibited a metastable tetragonal (t′) structure. The hot-corrosion behavior of the GdYb–YSZ TBCs was investigated at 700, 800, 900, and 1000 °C for 10 h in the presence of V2O5 molten salt. During the corrosion tests, the t′ phase transformed into a monoclinic (m) phase; nevertheless, it was still detected on the corroded surfaces. The amount of t′ phase decreased with increasing corrosion temperature. The corrosion products formed on the GdYb-YSZ TBCs in V2O5 comprised Yb, Gd-doped YVO4, and m-ZrO2, irrespective of the temperature of corrosion. However, higher temperatures changed the morphologies of the Yb- and Gd-doped YVO4 corrosion products. The GdYb–YSZ TBCs exhibited improved corrosion resistance to V2O5 molten salt when compared to YSZ TBCs, and the related mechanism is discussed in detail in this paper. Full article
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15 pages, 4123 KiB  
Article
Direct Fabrication and Characterization of Zirconia Thick Coatings on Zirconium Hydride as a Hydrogen Permeation Barrier
by Zhi-Gang Wang, Wei-Dong Chen, Shu-Fang Yan, Xue-Kui Zhong, Wen Ma, Xi-Wen Song, Ya-Ming Wang and Jia-Hu Ouyang
Coatings 2023, 13(5), 884; https://doi.org/10.3390/coatings13050884 - 8 May 2023
Cited by 2 | Viewed by 1506
Abstract
The present work attempted to produce thick zirconia coatings formed by micro-arc oxidation as a hydrogen permeation barrier on zirconium hydride alloy. A novel multiphase zirconia coating was achieved, exhibiting superior hydrogen permeation barrier performance. The growth dynamics, formation mechanism, and phase evolution [...] Read more.
The present work attempted to produce thick zirconia coatings formed by micro-arc oxidation as a hydrogen permeation barrier on zirconium hydride alloy. A novel multiphase zirconia coating was achieved, exhibiting superior hydrogen permeation barrier performance. The growth dynamics, formation mechanism, and phase evolution behavior of thick zirconia coatings were explored, and the hydrogen permeation barrier performance was evaluated by means of vacuum dehydrogenation experiment. The hydrogen desorption quantity was monitored by analyzing pressure changes with a quadruple mass spectrometer (QMS). Experimental results show that the multiphase coatings were composed of monoclinic ZrO2 (m-ZrO2), tetragonal ZrO2 (t-ZrO2), and a trace of cubic ZrO2 (c-ZrO2). The coatings were generally divided into a dense and uniform inner, intermediate layer, and a porous top layer. The quantitative analysis indicates an increased amount of m-ZrO2 toward the coating surface and an increased amount of t-ZrO2 toward the oxide/metal interface. This novel multiphase thick zirconia coating can noticeably improve hydrogen permeation resistance, and the permeation reduction factor (PRF) value is improved by nearly 13 times compared with bare zirconium hydride. It is demonstrated that hydrogen desorption is retarded to some extent in the presence of thick zirconia coating. Hydrogen desorption of the sample with ceramic coating started at 660 °C, which was apparently higher than that of the sample without coating. Full article
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15 pages, 3991 KiB  
Article
Prediction of Microstructure and Mechanical Properties of Atmospheric Plasma-Sprayed 8YSZ Thermal Barrier Coatings Using Hybrid Machine Learning Approaches
by Han Zhu, Dongpeng Li, Min Yang and Dongdong Ye
Coatings 2023, 13(3), 602; https://doi.org/10.3390/coatings13030602 - 12 Mar 2023
Cited by 5 | Viewed by 1535
Abstract
The preparation of thermal barrier coatings (TBCs) is a complex process involving the integration of physics and chemistry, mainly involving the flight behavior and deposition behavior of molten particles. The service life and performance of the TBCs were determined by various factors, especially [...] Read more.
The preparation of thermal barrier coatings (TBCs) is a complex process involving the integration of physics and chemistry, mainly involving the flight behavior and deposition behavior of molten particles. The service life and performance of the TBCs were determined by various factors, especially the preparation process parameters. In this work, to set up the quantitative characterization model between the preparation process parameters and the performance characteristic parameters, the ceramic powder particle size, spraying power and spraying distance were treated as the model input parameters, the characteristic parameters of microstructure properties represented by the porosity, circularity and Feret’s diameter and the mechanical property represented by the interfacial binding strength and macrohardness were treated as the model output. The typical back propagation (BP) model and extreme learning machine (ELM) model combined with flower pollination algorithm (FPA) optimization algorithm were employed for modeling analysis. To ensure the robustness of the obtained regression prediction model, the k-fold cross-validation method was employed to evaluate and analyze the regression prediction models. The results showed that the regression coefficient R value of the proposed FPA-ELM hybrid machine learning model was more than 0.94, the root-mean-square error (RMSE) was lower than 2 and showed better prediction accuracy and robustness. Finally, this work provided a novel method to optimize the TBCs preparation process, and was expected to improve the efficiency of TBCs preparation and characterization in the future. Full article
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31 pages, 9756 KiB  
Article
Evaluation of Solid Particle Erosion of EB-PVD TBCs under Thermal Cycling Conditions Based on a Stochastic Approach
by Bochun Zhang, Kuiying Chen and Natalie Baddour
Coatings 2023, 13(1), 156; https://doi.org/10.3390/coatings13010156 - 11 Jan 2023
Viewed by 1042
Abstract
The solid particle erosion behavior of electron-beam physical vapor deposition (EB-PVD) thermal barrier coatings (TBCs) was numerically evaluated under thermal cycling conditions. The erosion rates were calculated based on the mechanics-based formulae where the model parameters are fitted to the temperature-process-dependent test data [...] Read more.
The solid particle erosion behavior of electron-beam physical vapor deposition (EB-PVD) thermal barrier coatings (TBCs) was numerically evaluated under thermal cycling conditions. The erosion rates were calculated based on the mechanics-based formulae where the model parameters are fitted to the temperature-process-dependent test data available in the literature. A stochastic approach was applied to simulate the erosion behavior toward service conditions. The mechanics-based formulae were then validated by experimentally measured temperature and sintering-dependent erosion rates from the literature. The pseudoductile erosion behavior is identified for silica particles in the EB-PVD topcoat (TC) erosion system above the intermediate temperatures (~220 °C) due to the softening of partial molten silica particles, thus leading to an increase in the cutting wear and a decrease in deformation wear. The erosion rates are found to decrease versus temperature but increase versus thermal cycles. Such erosion behavior could be attributed to propagation of sintering cracks induced at elevated temperatures. The parametric calculations show that both erosion and thermal cycling parameters have a profound effect on the erosion mechanism of EB-PVD TC. The erosion rate increases at higher solid particle velocity and accumulated mass but displays a pseudoductile erosion behavior versus variation of impacting angles. Two types of erosion mechanisms were evaluated under different thermal cycling conditions. Under the burner cycling test with a short high-temperature dwell period, the erosion mechanism of EB-PVD TBCs is governed by temperature, while under an isothermal cycling test with a high-temperature long dwell period, the erosion is determined by sintering time. The failure mechanisms of EB-PVD TBCs under solid particle erosion processes are discussed combining internal cracking within topcoat and external erosion on the surface of topcoat. Full article
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10 pages, 2585 KiB  
Article
Phase Composition and Stability, Sintering and Thermal Conductivity of Gd2O3 and Yb2O3 Co-Doped YSZ
by He Tian, Liangliang Wei and Limin He
Coatings 2023, 13(1), 53; https://doi.org/10.3390/coatings13010053 - 28 Dec 2022
Cited by 1 | Viewed by 1516
Abstract
Y2O3-stabilized ZrO2 (YSZ) has been the material of choice for thermal barrier coatings (TBCs) in the past decades, yet its phase decomposition limits its application above 1200 °C. In this study, Gd2O3 and Yb2 [...] Read more.
Y2O3-stabilized ZrO2 (YSZ) has been the material of choice for thermal barrier coatings (TBCs) in the past decades, yet its phase decomposition limits its application above 1200 °C. In this study, Gd2O3 and Yb2O3 co-doped YSZ powders were produced, in which some amounts of monoclinic (m) phase were introduced into the cubic (c) phase matrix. XRD results showed that the fabricated powders obtained by a solid phase synthesis were composed of m and c phases, and hat the m phase content decreased in a sequence of 4Gd-2Yb-4Y, 2Gd-2Yb-6Y and 2Gd-4Yb-4Y powders. This indicated that Yb3+ is an excellent stabilizer in the ZrO2-based lattice, which could largely suppress the formation of the m phase. The m phase content in the powders was almost kept unchanged with heating at 1300 °C, which could provide a toughening effect to the ceramic. All the powders exhibited no obvious sintering at 1300 °C for 150 h. As compared to YSZ, the three fabricated ceramics had lower thermal conductivities, and they increased in a sequence of 4Gd-2Yb-4Y, 2Gd-4Yb-4Y and 2Gd-2Yb-6Y. Full article
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13 pages, 14364 KiB  
Article
Predicting the Residual Stress of Amorphous Al2O3-Y2O3 Nano-Laminated Deuterium Permeation Barrier under Thermal Cycles
by Kezhi Huang, Hao Liu, Weijing Wang, Qinghe Yu, Liwu Jiang, Yu Liu, Jing Mi, Lei Hao, Baolong Yuan, Mingkun Liu, Rui Cai and Wei Xiao
Coatings 2022, 12(11), 1780; https://doi.org/10.3390/coatings12111780 - 21 Nov 2022
Viewed by 1240
Abstract
Al2O3-Y2O3 laminated coating can be applied in fusion reactors to prevent fuel leakage and radiological hazard. However, the residual stress induced by the thermal cycles during the operation of the reactor can cause the failure of [...] Read more.
Al2O3-Y2O3 laminated coating can be applied in fusion reactors to prevent fuel leakage and radiological hazard. However, the residual stress induced by the thermal cycles during the operation of the reactor can cause the failure of the coating. In order to analyze the problem, finite element models of Al2O3-Y2O3 laminated coatings with 600 nm of total thickness and different layout were analyzed. The max principal stress site in the coatings is located at the sub-top layer. The max principal stress in laminated coating with the Y2O3 sub-top decreases from 657 MPa for a two-layer coating (300 nm) to 598 MPa for a four-layer coating (150 nm). On the contrary, if Al2O3 is the sub-top layer, the max principal stress increases from 463 MPa for a two-layer coating (300 nm) to 495 MPa for a four-layer coating (150 nm). The result shows that the more deformable amorphous Al2O3 layer in the laminated coating system is more influential to the thermal stress. Full article
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Review

Jump to: Research

16 pages, 19080 KiB  
Review
Effect of Pre-Heat-Treatment on the Oxidation Resistance of MCrAlY Coatings: A Review
by Bangyan Zhang, Shijie Zheng, Jiajian Dong, Weiwei Yin, Hongbin Wu, Lixi Tian and Guangming Liu
Coatings 2023, 13(7), 1222; https://doi.org/10.3390/coatings13071222 - 8 Jul 2023
Cited by 1 | Viewed by 1213
Abstract
High-performance gas turbines and aircraft engines necessitate MCrAlY (M = Ni, Co, or Ni/Co) coatings with exceptional oxidation resistance. Pre-heat-treatment can enhance the performance of MCrAlY bond coatings in the following ways: First, it reduces the porosity of the bond coating and promotes [...] Read more.
High-performance gas turbines and aircraft engines necessitate MCrAlY (M = Ni, Co, or Ni/Co) coatings with exceptional oxidation resistance. Pre-heat-treatment can enhance the performance of MCrAlY bond coatings in the following ways: First, it reduces the porosity of the bond coating and promotes the diffusion of elements within it. Second, pre-heat-treatment allows for the formation of a continuous, dense, and moderately thick layer of pure Al2O3 scale, which helps to delay the formation of mixed oxides. Lastly, proper pre-heat-treatment can increase the grain size of the Al2O3 scale, leading to a lower growth rate of the oxide scale. Additionally, this article proposes new directions for developing more reasonable and effective pre-heat-treatment methods, laying the foundation for the creation of thermal barrier coatings (TBCs) with greater durability and higher performance. Full article
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