Properties Of Thermal Barrier Coatings Research Articles

Terahertz Nondestructive Measurement of Heat Radiation Performance of Thermal Barrier Coatings Based on Hybrid Artificial Neural Network

Effective control of the micro- and nanostructure of thermal barrier coatings is essential to enhance the thermal radiation performance of the coating, which helps to determine the remaining service life of the coating. This paper proposed a method to measure the radiation properties of thermal barrier coatings by terahertz nondestructive testing technique, using APS-prepared thermal barrier coatings as the object of study. Radiative properties were a comprehensive set of properties characterized by the diffuse reflectance, transmittance, and absorptance of the thermal barrier coating. The coating data in actual service were obtained by scanning electron microscopy and metallographic experiments, and the data were used as the simulation model critical value. The terahertz time-domain simulation data of coatings with different microstructural features were obtained using the finite-different time-domain (FDTD) method. In simulating the real test signals, white noise with a signal-to-noise ratio of 20 dB was added, and fast Fourier transform (FFT), short-time Fourier transform (STFT), and wavelet transform (WT) were used to reduce the noise and compare their noise reduction effects. Different machine learning methods were used to build the model, including support vector machine algorithm (SVM) and k-nearest neighbor algorithm (KNN). The principal component algorithm (PCA) was used to reduce the dimensionality of terahertz time-domain data, and the SVM algorithm and KNN algorithm were optimized using the particle swarm optimization algorithm (PSO) and the ant colony optimization algorithm (ACO), respectively, to improve the robustness of the system. The K-fold cross-validation method was used to construct the model to improve the adaptability of the model. It could be clearly seen that the novel hybrid PCA-ACO-SVM model had superior prediction performance. Finally, this work proposed a novel, convenient, nondestructive, online, safe and highly accurate method for measuring the radiation performance of thermal barrier coatings, which could be used for the judgment of the service life of thermal barrier coatings.

The effects of phase interfaces in SmFeN/YSZ composite thermal barrier materials on electromagnetic wave-absorbing properties

Yttria-stabilized zirconia (YSZ) oxide ceramic powder is a thermal-barrier material used to fabricate thermal barrier coatings (TBC). In this study, to improve the electromagnetic wave (EMW) absorbing properties of TBCs, microwave-absorbing samarium iron nitrogen (SmFeN) particles were used to prepare SmFeN/yttria-stabilized zirconia (YSZ) composites. To study the effect of the SmFeN/YSZ interfaces on the EMW-absorbing properties of the SmFeN/YSZ composite, SmFeN/YSZ interfaces were built in different ways in composite materials having the same mass ratio of 1:1, for example, SmFeN and YSZ particles homogeneously mixed together, SmFeN/YSZ interfaces perpendicular and parallel to the EMW incident direction, and different interfaces between YSZ and SmFeN. Thus, the microwave absorbing performance of the samples, including the electromagnetic parameters, attenuation coefficient, eddy-loss current (C0), impedance matching, and minimum reflection loss (RLmin) values were examined and analyzed. The results demonstrate that interfaces perpendicular to the direction of the EMWs can increase the contact area and enhance the interfacial absorption effect. Further, when the wave-absorbing agent was placed in the middle of the composite, its wave-absorbing effect was the best among all the samples, yielding RLmin = −27.824 dB and effective absorption bandwidth (EAB) = 8.5453 GHz (effective absorption frequency range 7.9256–16.4709 GHz for a 7.2-mm-thick layer). Crucially, the frequency and bandwidth at which the best absorption occurred could be tuned by adjusting the thickness of the coating. This is because the interfaces in the samples resulted in polarization enhancement and anomalous dispersion, leading to large dielectric losses. Overall, the use of a coaxial measurement technique is highly efficient for EMW absorbing body design and process simulations.

Mechanical evaluation of thermal barrier coatings by indentation: A review

Thermal barrier coatings (TBCs) play an important role in the thermal protection of alloy components in high temperature industries. Accurately characterizing and extracting mechanical properties of TBCs are crucial for structural design, performance optimization, failure prediction and lifespan assessment. Indentation test is an effective method for experimentally obtaining the mechanical properties and provides valuable insights into the elastic, plastic and fracture behaviors of TBCs at elevated temperatures. This paper aims to provide an overview of indentation mechanical evaluation of TBCs, including the mechanical properties at different temperatures, the mechanical property anisotropy, the microstructural and mechanical behavior under thermal exposure and/or thermal cycling, as well as the comparison of functional performance between conventional and nanostructured TBCs. Furthermore, this paper points out the main challenges and future directions from indentation investigations of TBCs. Finally, this paper is summarized and prospected.

Effect of sintering on stress distribution of thermal barrier coatings for high temperature blade

In the process of long-term high temperature service, thermal barrier coatings (TBCs) will inevitably be sintered, leading to pores healing and porosity decline, which will affect the microstructure and the stability of mechanical properties of TBCs. To understand the relationship between the microstructural changes of sintered TBCs and the mechanical properties, in this work, the cross-sectional microstructure of TBCs at different sintering times were investigated by scanning electron microscopy (SEM). After calculating the porosity and pore size distribution, two-dimensional (2D) numerical models were developed for five different porosities (16 %–12 %) by an improved reconstruction method with layer-by-layer labeling. Based on the results of finite element (FE) analysis after thermal cycling, it was found that the coating's irregular pore structures lead to stress concentration, which affects the mechanical properties of the coating to a great extent. For the whole TC layer, the level of stresses increases and the absolute value of maximum stress augments significantly by 46 % associated with the doubled increase of stress concentration areas with the densification of coating. For the local areas of TC layer, the changes in pore morphology led to a more complex variation in local stress fields. At the TC/BC interface, the Mises stress level tends to increase with decreasing porosity during sintering. At the TC surface, coatings with lower porosities cause higher stresses near this region. The insights gained from the numerical results contribute to a better understanding of the failure behavior of real TBCs systems and help to further remedy the deficiencies and difficulties of the experimental work.

Evaluation of Coating Properties of Thermal Barrier Coatings by Leeb Hardness Testing

Evaluation of Coating Properties of Thermal Barrier Coatings by Leeb Hardness Testing

Deposition characteristics, sintering and CMAS corrosion resistance, and mechanical properties of thermal barrier coatings by atmospheric plasma spraying

Atmospheric plasma spraying (APS) was used to fabricate 4.5 mol% Y2O3 stabilized ZrO2 (YSZ) and 4.0 mol% Yb2O3 and 0.5 mol% Y2O3 co-stabilized ZrO2 (YbYSZ) series coatings with different spraying parameters. This study presents the effects of particle size of feed powder and substrate temperature on the microstructure and performance of thermal barrier coatings. Single-pass and multi-pass experiments were conducted to explore the relationship between the splat and the coatings. The experimental results indicate that adjusting particle size of feed powders and deposition temperature can alter the splat behaviour and microstructure, improve anti-corrosion and anti-sintering abilities, and enhance the hardness and elastic modulus. Changes in parameters can cause changes in the microstructure of as-sprayed coatings. Lower substrate temperatures can lead to vertical cracks, finer powders can introduce more microdefects, and conventional sized powders can form larger pores. A coating deposited using a conventional feed powder at a substrate temperature of 800 °C shows excellent sintering resistance. A coating deposited using a fine feed powder on 800 °C substrate exhibits the best calcium‑magnesium-alumina-silicate (CMAS) corrosion resistance.

Effects of Top Ceramic Layers with an Ultrathin Dense Layer on the Thermal–Physical Properties of Thermal Barrier Coatings

Thermal barrier coatings have been used to protect superalloys under extremely harsh conditions. The durability of TBCs with a NiCoCrAlY bond layer prepared via the air plasma spray process and an ultrathin dense layer prepared via magnetron sputtering was investigated under different corrosion conditions. This paper discusses the corrosion resistance improvement mechanism of TBCs with a dense layer produced by magnetron sputtering under corrosion conditions with environmental contaminants such as calcium–magnesium–aluminum–silicon oxide systems (CMAS) at 1300 °C and NaCl-Na2SO4-V2O5 (NV) at 900 °C. The corrosion results show that CMAS will react with the stabilizers of zirconium oxide, which will change the rate of the phase transition, as determined via X-ray diffraction tests. A thermal ablation test verified that TBCs with a dense layer have a better corrosion resistance and better thermal insulation properties. All results show that preparing TBCs with a dense layer via the magnetron sputtering method will be an efficient method to improve TBCs’ properties at high temperatures in the future.

Investigations on the water-jet guided laser scribing of thermal barrier coated IC21 nickel-based superalloy

Ceramic thermal barrier coatings (TBCs) are widely recognized as state-of-the-art for ensuring the stability and reliability of turbine blades operating in extreme conditions. However, the significant disparities between the thermal and mechanical properties of TBCs, bonding layers (BCs), and nickel-based superalloy substrates pose considerable challenges for machining film cooling structures on turbine blades while minimizing coating delamination, heat-affected zones (HAZs), and other potential defects. The utilization of Water-Jet Guided Laser (WJGL) has gained significant attention as a promising approach for the machining of advanced materials, including ceramics and multi-layer composites. In this study, a theoretical model is proposed to describe the transient interaction between WJGL and TBC IC21 nickel-based superalloy. A numerical simulation using the deformation geometry method is employed to investigate the evolution of ablation morphology, which is further validated by experimental data. Specifically, the formation mechanism of the shoulder structure at the material interface is explained. Furthermore, orthogonal experiments are conducted to establish the fundamental influence rule and significance level of machining parameters on the microscopic groove morphology. Based on these findings, multi-row cutting experiments are performed to identify the optimized scanning trajectory for achieving the high-quality thorough cutting of the substrate with a thickness of 2.7 mm, while minimizing oxidation, residue deposition, and delamination. The outcomes of this study contribute to the knowledge of WJGL machining, and could potentially improve the efficiency and accuracy of advanced material processing techniques.

Influence of Microalloying Elements on the Structures and Properties of Thermal Barrier Coatings on Gas Turbine Blades

Influence of Microalloying Elements on the Structures and Properties of Thermal Barrier Coatings on Gas Turbine Blades

Effect of CMAS infiltration on the optical properties of thermal barrier coatings: Study of the mechanisms supported by FDTD simulations and ALD

Effect of CMAS infiltration on the optical properties of thermal barrier coatings: Study of the mechanisms supported by FDTD simulations and ALD

Study on Microstructure and Properties of Thermal Barrier Coating for Gas Turbine

Thermal barrier coating (TBC), which can protect the metallic components from hot gas, is one of the core technologies to achieve the development goal of higher thermal efficiency and lower emission for gas turbine. A double-coat TBC was prepared on the Mar M247 substrate of turbine blade for gas turbine which consisted of a CoNiCrAlY bond coat(BC) was prepared by high velocity oxygen fuel(HVOF) and a ZrO2-8Y2O3(8YSZ) top coat(TC) was prepared by atmospheric plasma spraying (APS).The microstructure of the TBC was analyzed by optical microscope(OM) and scanning electron microscope(SEM), and the thermal insulation and thermal shock resistance of the TBC were investigated. The results show that the homogeneous and fine microstructure in TBC is obtained,the interfacial bonding between the top coat and the bond coat, between the bond coat and the substrate is well. The thermal insulation temperature can reach 156°C,under the condition of test temperature of 1150°C and cooling air flow of 4 m3/h. And the thermal shock resistance is greater than 100 cycles at the test condition of 1050 °C.

Effect of CMAS Infiltration on the Optical Properties of Thermal Barrier Coatings: Study of the Mechanisms Supported by FDTD Simulations and ALD

Effect of CMAS Infiltration on the Optical Properties of Thermal Barrier Coatings: Study of the Mechanisms Supported by FDTD Simulations and ALD

Investigation of vermiculite infiltration effect on microstructural properties of thermal barrier coatings (TBCs) produced by electron beam physical vapor deposition method (EB-PVD)

Thermal barrier coatings (TBCs) are protective coating systems that are mostly utilized to improve the thermal insulation and functional performance of gas turbine engines and other aircraft components that are both stable and movable. These coatings protect materials operating in harsh conditions from structural damage caused by corrosion, oxidation, the CaO-MgO-Al2O3-SiO2 effect (CMAS), thermal shock, volcanic ash, and vermiculite deposits at high temperatures. In this study, CoNiCrAIY metallic bond coatings were coated on Inconel 718 super alloy using a high velocity oxygen-fuel (HVOF) deposition technique. Then, single YSZ, Gd2Zr2O7 (GZ), and double YSZ/GZ based ceramic topcoats were applied to the bond coats by using the electron beam physical vapor deposition (EB-PVD) method. The produced TBC samples and the uncoated Inconel 718 superalloy substrate were subjected to vermiculite (VM) deposition at 1250 °C for 4 h, and then the coatings were characterized. To determine the phase structures, microstructural and mechanical properties of the TBCs, X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer elemental mapping analysis (EDS), stereo microscopy analyses, porosity, and hardness measurements were used. The obtained results were comparatively evaluated with the recent related studies in the literature.

Effect of isothermal heat treatment on nanoindentation hardness and Young’s modulus of 4 mol% Y2O3-ZrO2 EB-PVD TBCs

4 mol% Y2O3–ZrO2 (4YSZ) is commonly used in thermal barrier coatings (TBCs) for high-temperature applications such as gas turbine engines. This study was investigated the effects of heat treatment at 1400 °C for 0, 2, 20, and 100 h on the hardness and Young’s modulus of 4YSZ coatings prepared by electron-beam physical vapor deposition. Nanoindentation measurements were performed on the top and side surfaces of the coating. The as-coated and the heat-treated coatings exhibited strong anisotropy in the mechanical properties; the hardness and Young’s modulus of the side surface of the coatings were lower than those of the top surface. Increasing the heat treatment time was found to increase the hardness and Young’s modulus in both the directions. This is correlated with the decrease in porosity with increase in the heat-treatment time and closure of gaps between the columns and arms of their (as-coated) featherlike microstructures, which are known to deleteriously affect both the toughness and thermal insulating properties of TBCs.

Effect of material characteristics on thermal, tribological and mechanical properties of high temperature cast iron coatings

Coating is a desideratum part of material science and effort must be entailed for obtaining desired high temperature properties. Properties of high temperature cast iron coatings depend on various factors and each of them must be precisely tailored for meeting the huge industrial demand. The unlimited architecture of novel materials has led to growth of various coating with tailored properties. Single/multi layered structure offers remarkable possibilities to improve coating properties. Cast iron has been increasingly used in gas turbine, internal combustion engine manufacturing industries due to its low cost and structural strength. Numerous researches have been done on cast iron coatings to study the thermal, tribological plus mechanical properties. Novel material for improving the thermal, mechanical and tribological properties of Thermal barrier coatings (TBCs) required an extensive property-characteristics connection realization. Yttria Stabilized Zirconia (YSZ) is the most established coating material for thermal barrier application. YSZ alone cannot withstand the huge industrial demand. YSZ in engine application suffers failure due to non-uniform thermal field, thermal stress and sintering during the cycle of operation. YSZ cannot withstand engine thermal properties including thermal cycle life and thermal durability. Wear rate gets affected as a result of brittle fracture, speed of operation and abrasion. High temperature exposure leads to microcracks and this affects the mechanical properties. TBCs are usually made of ceramic top coat and it suffers failure. Few material characteristics and factors include thermal aging, fracture toughness of the material. This paper summarizes confirmed experimental results by researchers concerning different factors including thermal conductivity, thermal shock resistance, thermal cycle life, wear resistance, coefficient of friction, hardness and material characteristics in regard with cast iron coatings for high temperature applications. This paper also recommends feasible materials and material combinations to overcome certain limitations and failures.

Effect of microstructure on thermal cycle fatigue resistance in a SPS-TBC

The turbine blades of gas turbine engines used in thermal power plants are coated with a thermal barrier coating (TBC) made of ceramics to provide heat resistance. In recent years, gas turbines for power generation have been utilized as a regulating power source for engines, which are subject to frequent start-up and shutdown and output fluctuations. In this context, the suspension plasma spraying (SPS) method, which has been developed recently, has been studied intensively because it has a porous columnar structure and superior thermal cycle properties compared with the conventional atmospheric plasma spraying method. In this study, we evaluated the thermal cycle properties of TBCs with different microstructures prepared by varying the deposition conditions of the SPS method, and investigated the effect of microstructures on the thermal cycle properties. The experimental results indicated that the thermal cycle fatigue life of SPS-TBC increased with decreasing column diameter. The effect of microstructure on the thermal cycle fatigue life was discussed based on the thermal stress in top-coating evaluated by the FE analysis.

Effect of Heat Treatment on Microstructure and Thermal Conductivity of Thermal Barrier Coating.

Thermal barrier coatings (TBCs) are essential for increasing the inlet temperature of gas turbines to improve their thermal efficiency. Continuous exposure to flames is known to affect the thermal properties of TBCs, degrading the performance of gas turbines as a consequence. In this study, we quantified the changes in the thermal conductivity of yttria-stabilized zirconia coatings with respect to various heat treatment temperatures and times. The coating exhibited an increase in thermal conductivity after heat treatment, with higher heat treatment temperatures resulting in greater thermal conductivity. The coatings were analyzed by X-ray diffraction and scanning electron microscopy before and after heat treatment. Results showed that there was little change in thermal conductivity due to phase changes and grain size. We conclude that pore structures, i.e., circular and lamellar pores, affected the change in thermal conductivity. Specifically, we confirmed that the change in thermal conductivity depends on the size of the lamellar pores.

EFFECT OF HOT CORROSION AND OXIDATION ON COBALT - BASE SUPERALLOYS COATED BY ALUMINUM WITH PRESENCE OF THERMAL BARRIER ZRO2 AND MIXTURE OF (NACL) AND (NA2SO4) STEAMSALTSAT HIGH TEMPERATURES

The aim of the study was to investigate the Mechanisms properties of thermal barrier coatings (TBCs) to enhance of performance evaluation characteristics and develop TBCs.Cobalt –base superalloy has been used as a substrate and zirconium stabilized Aluminum as ceramic topcoat , in addition the study include degradation behavior of system during thermal cycling (3hr per cycle in furnace) the failure of the aluminized was due to thermally grown oxide (TGO) interface. The fractures propagatethrough the interface and produce a deformation of the bond coating . the effect of cycle will result a spallation failure of the TBCsand this is also corresponding to a slightdegradation .The steam of salt (Nacl)and(Na2So4) mixture will affecton the coating lifetimes .The high temperature have a strong effect thermally grown oxide (TGO) which consistent with a first order growth of scale failer variation.

Bonding and Thermal-Mechanical Property of Gradient NiCoCrAlY/YSZ Thermal Barrier Coatings with Millimeter Level Thickness

The thermal insulation properties of thermal barrier coatings (TBCs) can be significantly improved with increasing the coating thickness. However, due to the weak bonding of high-thickness TBCs, the low reliability and short lifetime greatly limits their application under some severe operating conditions. In this study, a novel and high-efficiency synchronous dual powder feeding method is used to deposit a series of gradient NiCoCrAlY/YSZ coatings with millimeter level thickness. The tensile bonding strengths and residual stress state of coatings are evaluated in order to explore the effect of thickness on the bonding strength of coatings. The results suggested that, due to some micro-convex structure at the “GC/TC” interface and inside “GC” layer, the bonding strength of 1000-μm-thickness gradient NiCoCrAlY/YSZ TBCs with the 4:6 and 2:8 hybrid ratios is over 44 MPa compared to the common TBCs. The fracture position gradually shifts from NiCoCrAlY bond coat to NiCoCrAlY/YSZ transition zone and finally to the YSZ top coat owing to the different position of residual stress concentrations. After thermal cycling tests, the 1000-μm-thickness gradient coating exhibits a higher thermal cycling life. Some coarse cracks initiate and propagate at the bottom region of TBCs, which is mainly due to thermal expansion mismatch stress that finally results in the failure of the gradient coating between the “BC” layer and the substrate.

Microstructures and Thermal Cycling Properties of Thermal Barrier Coatings Deposited by Hybrid Water-Stabilized Plasma Torch

Hybrid water-stabilized plasma (WSP-H) torches provide high-enthalpy plasma which may be utilized for high-throughput and yet economical spraying of coatings from powders, suspensions, and solutions. It was previously demonstrated that microstructures and functional properties of the WSP-H coatings may be tailored to a wide extent for new applications, namely those requiring high coating thickness and/or coating of large components. In this study, applicability potential of WSP-H technology for spraying of novel thermal barrier coatings (TBCs) is demonstrated. WSP-H technology was used for spraying of yttria-stabilized zirconia (YSZ) top-coats from powder, suspension, and solution. Yttria content in the top-coat feedstock was 7-8 wt.%. In addition, gadolinium zirconate (Gd2Zr2O7-GZO) was sprayed from suspension for comparison. NiCrAlY bond-coat was also deposited by WSP-H, and Hastelloy-X alloy was used as substrate material. Microstructure, phase composition, and endurance of the deposited coatings in thermal cycling fatigue (TCF) test and during high-temperature short-term annealing were evaluated. All coatings showed excellent high-temperature stability and TCF resistance withstanding more than 650 cycles, surpassing some of the currently commercially used TBCs. Lifetime of the TBC with columnar top-coat deposited from YSZ suspension exceeded even more than 900 cycles.