Search Results (285)

Owing to their exceptional thermal insulation and protective capabilities, thermal barrier coatings (TBCs) are widely applied to critical hot-section components of aero-engines. However, under increasingly harsh service environments, internal defects such as delamination tend to form within the coatings, posing a severe threat to engine operational safety and service life. To effectively evaluate delamination defects in TBCs, this study employs the immersion ultrasonic pulse-echo technique to inspect specimens subjected to various thermal cycling treatments. Four specimens, subjected respectively to 21, 32, 43, and 54 thermal cycles at 1200 °C, were tested. Ultrasonic response data were systematically acquired via normal incidence scanning from both the superalloy substrate side and the ceramic top coat side. Combining Fast Fourier Transform (FFT), Continuous Wavelet Transform (CWT) based on the generalized Morse wavelet, Wavelet Packet Energy Entropy (WPEE), and peak-to-peak amplitude variations of the second echo, multi-dimensional features were extracted from ultrasonic signals across the frequency domain, joint time-frequency domain, and energy distribution profiles. Through comparative analysis, ultrasonic waveform and time-frequency characteristics representing defect evolution were obtained. A significant monotonically decreasing trend of WPEE with the aggravation of interfacial delamination was established, characterizing the acoustic energy confinement process induced by interfacial damage. Furthermore, a multilayer finite element (FE) model reasonably reproduced dynamic acoustic wave propagation; numerical results are in agreement with experimental data, validating the feasibility of the proposed detection method. The detection and evaluation framework established in this study provides a reference for safety monitoring and lifespan prediction of aero-engine TBCs. Full article

The cooling performance of turbine vanes with thermal barrier coatings (TBCs) is significantly affected by the flow distribution of internal cooling channels. To investigate the influence of channel flow distribution on the vane cooling characteristics, this study adopts the Latin hypercube sampling method to realize differentiated flow distribution of each cooling channel under a nearly constant total cooling flow rate. Numerical simulations are performed to obtain vane cooling characteristic data under various flow distribution schemes, followed by multi-condition quantitative comparison and mechanism analysis. The results show that the trailing edge channel serves as the dominant factor controlling the overall vane temperature, while the middle channels exhibit obvious cooling redundancy. Specifically, the flow rates of the leading edge arc and trailing edge dominate the peak temperature and average temperature of the suction surface, respectively. Unlike geometric optimization that alters vane internal structures, this study focuses on flow redistribution under the strict constraint of fixed total cooling air consumption. This strategy offers a zero-cost approach to cooling enhancement for in-service turbines with no structural modifications required. The cooling benefit is enhanced without additional cooling air consumption. The overall surface peak temperature is reduced by 0.4%. By region, the peak temperatures of the pressure surface and the suction surface reduced by 0.40% and 0.435% respectively, and the leading edge arc reduced by 0.20%. The overall average surface temperature has reduced by 0.117%. The research conclusions can provide a theoretical reference for the flow optimization of turbine vane cooling channels and the improvement of overall cooling uniformity, which is qualitatively beneficial to reducing the thermal failure risk of coatings. Full article

Yttria-stabilized zirconia (YSZ) thermal barrier coatings suffer from t′ phase destabilization and insufficient thermal insulation above 1200 °C. In this work, YbO_1.5-stabilized ZrO₂ powders (xYbSZ, x = 4–12 mol% YbO_1.5 on a cation basis, equivalent to 2–6 mol% Yb₂O₃) were synthesized by chemical co-precipitation, consolidated by spark plasma sintering, and evaluated at 1300 °C in terms of phase stability, sintering behavior, thermal conductivity, and fracture toughness. A common compositional boundary near 8 mol% YbO_1.5 was identified across all four responses. 8YbSZ retained the metastable t′ phase with a monoclinic content below 10 mol% after 300 h at 1300 °C, whereas grain coarsening accelerated markedly and the thermal conductivity reduction efficiency per unit doping at 1000 °C was approximately halved beyond this composition, with κ decreasing from 2.41 to 1.96 W·m⁻¹·K⁻¹ across the series. The toughness gain produced by thermal treatment fell from 34% (4YbSZ) to about 10% (10–12YbSZ) as the dominant toughening mechanism shifted from transformation and microcrack toughening (4–6 mol%) to ferroelastic domain switching (8 mol%), with both being lost in the compositions in which the cubic phase predominated. These results identify 8 mol% YbO_1.5 as the optimal composition balancing phase stability, sintering resistance, thermal insulation, and mechanical integrity for TBC applications at 1300 °C. Full article

In this study, 8YSZ thermal barrier coatings (TBCs) were deposited on IC21 single-crystal superalloy substrates. Short-term overheating at 1300 °C was conducted for durations of 1, 5, and 10 min under both uniform temperature and simulated service conditions, followed by thermal cycling and thermal shock tests, respectively, to investigate the short-term overheating behavior of the coatings. The effects of short-term overheating on microstructural evolution and stress evolution under different conditions were analyzed, and the underlying damage mechanisms were determined. The results show that under uniform temperature conditions, short-term overheating drives the continuous growth of the thermally grown oxide (TGO). Coating failure occurs at the specimen edge, dominated by thermal stress concentration induced by geometric edge effects. The stress evolution is relatively mild, and the damage mechanism is primarily long-term interfacial degradation. Under simulated service conditions, short-term overheating induces sintering and cracking in the ceramic top coat. Coating failure occurs at the specimen center, dominated by crack coalescence. Transient temperature gradients generate high non-steady-state thermal stresses. The damage mechanism involves thermomechanical loading accelerating interfacial degradation, with synergistic effects of ceramic layer sintering and TGO destabilization, leading to a significant reduction in coating lifetime. Full article

To investigate the influence of particle size on the erosion damage behavior and failure mechanisms of thermal barrier coatings (TBCs) in a simulated aero-engine erosion environment, erosion tests were conducted using Al₂O₃ particles of different sizes (65 μm, 120 μm, and 175 μm) under a nominal gas-flow condition of Mach 0.4 at 1150 °C with custom-built multi-factor coupled erosion test equipment. TBCs were prepared using electron beam physical vapor deposition (EB-PVD). By combining macroscopic/microscopic morphology, composition, white-light interferometry, and Raman residual stress testing, the damage evolution and failure behavior of TBCs under different particle size conditions were analyzed. The results indicate that particle size has a significant effect on the erosion behavior of thermal barrier coatings. Under erosion conditions involving 65, 120, and 175 μm particles, the erosion rates were 10.83, 4.19, and 2.05 g/kg, with corresponding coating lifetimes of approximately 3, 12, and 22 h. As particle size increases, the erosion rate decreases and the coating lifetime increases. Under small 65 μm particles, the coating exhibits high-frequency continuous micro-cutting. The ceramic layer rapidly thins, leading to localized penetration. Under erosion by 120 μm particles, the coating exhibits a composite damage mechanism involving cutting, compaction, and brittle fracture. Under large-particle impacts of 175 μm, the damage mechanism is dominated by localized brittle fracture and spalling induced by high-energy impacts. Although the single-impact energy of large-particle impacts is higher, the lower particle number density results in a discrete distribution of damage zones, leading to a lower material removal rate. The Raman test results further indicate that, after 2 h of erosion, the differences in residual stress in the TGO layer were relatively small across different particle size conditions, suggesting that the early degradation process of the coating is primarily controlled by the mechanical removal of the ceramic surface layer rather than by the evolution of TGO stress. No statistically significant difference in TGO residual stress was observed among different particle sizes after 2 h of erosion (p > 0.05). Not only is the erosion life of EB-PVD YSZ TBCs is influenced by the impact energy of individual particles, but more importantly, it is also closely related to particle number density, impact frequency, and the spatial distribution of damage. Full article

In this article, an inverse mathematical model was developed to achieve fast and simultaneous estimation of thermophysical and geometric parameters for thermal barrier coating (TBC) systems in high-temperature environments with measurement errors. First, considering the convective and radiative heat transfer between the TBC system and the external environment, a one-dimensional unsteady conduction–radiation coupled heat transfer model was originally developed in high-temperature environments. Subsequently, this forward model was solved using the finite volume method (FVM), and the grid independence as well as the accuracy were validated. Thereafter, an accelerated inverse model, which adopts a principal component analysis (PCA)-optimized artificial neural network (ANN) to fit and substitute the forward model and employs the particle swarm optimization (PSO) algorithm for estimation, was developed based on the inverse method. Finally, under three different noise conditions, two situations were used to perform simultaneous estimation studies: a two-parameter case (top coat thermal conductivity and thermally grown oxide (TGO) layer thickness) and a three-parameter case (adding the thickness of an additional existing debonding defect layer). The results show that the PCA-optimized ANN-PSO-based accelerated inverse model is approximately 111–130 times faster than the traditional PSO-based inverse model, and the maximum relative errors of the arithmetic means of 20 estimations for two-parameter and three-parameter situations under three noise cases are on the order of 2.4% to 4.3%. Overall, the proposed accelerated inverse model achieves a favorable balance between speed and accuracy in multi-type parameter simultaneous estimation for TBC systems at high temperature, providing a methodological basis for addressing parameter estimation in more complex situations in future research. Full article

Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were fabricated by atmospheric plasma spraying (APS). Three CMAS powders with different compositions (CMAS-1, CMAS-2, CMAS-3) were selected, and corrosion tests were carried out at 1200 °C, 1250 °C, and 1300 °C. The relationships among CMAS viscosity, melting point, and reaction tendency with YSZ coatings were investigated. The results show that CMAS-3 possesses the highest viscosity yet the lowest melting point, CMAS-1 has the lowest viscosity but the highest melting point, and CMAS-2 falls between the two. Quantitative penetration depth measurements reveal that higher viscosity leads to slower infiltration, while a lower melting point enables earlier infiltration onset. At elevated temperatures, all CMAS compositions achieve complete penetration, indicating that the differences in melting point and viscosity become less critical when the temperature is sufficiently high. Corrosion tests reveal that CMAS-3 exhibits the strongest reaction tendency with YSZ coatings, while CMAS-1 shows the weakest. This indicates that the infiltration behavior is governed by a dual control of melting point and viscosity—melting point determines the onset of infiltration, while viscosity controls the penetration rate. This study provides an experimental basis for the design of CMAS-resistant coatings and the evaluation of their environmental adaptability. The key finding is that the melting point plays a dominant role in initiating CMAS infiltration, while viscosity primarily regulates the penetration rate. Full article

Thermal/environmental barrier coating (T/EBC) protects ceramic matrix composites (CMC) from environmental corrosion and provides thermal insulation simultaneously. As a newly developed TBC material, GdPO₄ has attracted much attention due to its low thermal conductivity, but its relatively high thermal expansion coefficient (TEC) limits the application in the T/EBC system. In this study, Yb-doped GdPO₄ with properties desirable for the T/EBC system is proposed. The high-temperature stability and mechanical and thermophysical properties of Gd_1−xYb_xPO₄ (x = 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875 and 1) were studied, and the mechanism for doping modification was fully explained. Gd_0.75Yb_0.25PO₄ with Young’s modulus of 82 GPa and thermal conductivity of 1.01 W·m⁻¹·K⁻¹ is considered to have the most desirable properties. Compared with GdPO₄, the TEC of Gd_0.75Yb_0.25PO₄ (6.3 × 10⁻⁶ K⁻¹) is reduced by ~39%, and the fracture toughness is improved by ~30%. Therefore, Gd_0.75Yb_0.25PO₄ is considered to be suitable for usage as a T/EBC material. Full article

To address the issue of depositing thermal barrier coatings (TBCs) on rotating curved surfaces, atmospheric plasma spraying (APS) was employed to prepare yttria partially stabilized zirconia (YSZ) coatings on a rotating curved substrate. Three standoff distances of 80 mm, 100 mm and 120 mm were selected. The microstructure, microhardness, elastic modulus and fracture toughness of three YSZ coatings were tested. The results indicate that as the standoff distance increased from 80 mm to 120 mm, porosity increased from 11.27% to 13.29%, microhardness decreased from 760.8 HV_0.3 to 713.2 HV_0.3, elastic modulus decreased from 24.0 GPa to 22.6 GPa, and fracture toughness decreased from 1.14 MPa·m^1/2 to 1.04 MPa·m^1/2. The properties of the YSZ coating in the case, such as elastic modulus and fracture toughness, were significantly lower than those of the YSZ coating deposited on stationary planar substrates. Solidification of the molten particles impacted on rotating curved substrates was accelerated and splat spreading was constrained because of the coupled effect of centrifugal force and elevated cooling rate. Therefore, under identical spraying parameters, the process parameters optimized for planar substrates cannot be directly transferred to rotating curved components. Full article

Advanced thermal barrier coatings (TBCs) are essential for improving the efficiency and performance of gas turbine engines. Increasing engine operating temperatures and harsh service environments are pushing the current industry-standard 8 wt% yttria-stabilized zirconia (8YSZ) to its performance limits. High-rare-earth-oxide zirconates, such as Gd₂Zr₂O₇, have emerged as promising materials for next-generation engines due to their excellent high-temperature phase stability, lower thermal conductivity, and enhanced resistance to CMAS attack. In this work, dense vertically cracked (DVC) Gd₂Zr₂O₇/8YSZ bilayer coatings were developed using the air plasma spray (APS) process. Two approaches were employed for deposition of the NiCrAlYHfSi bond coat: (i) high-velocity oxygen fuel (HVOF), and (ii) APS flash-coated HVOF NiCrAlYHfSi bond coat. The durability of DVC TBC systems with the two bond coat types was evaluated by furnace cycling test (FCT) at 1125 °C. The TBC system with an APS flash-coated HVOF bond coat exhibited an FCT lifetime approximately twice that of the system with the HVOF bond coat alone. The improvement is primarily attributed to the higher surface roughness of the APS flash-coated bond coat, which enhances resistance to crack initiation, propagation, and linkage, thereby extending thermal cycling life. Full article

With the continuous advancement of thrust-to-weight ratios in modern aero-engines, turbine inlet temperatures have reached levels that far exceed the thermal endurance limits of conventional superalloys and emerging ceramic matrix composites (CMCs). Consequently, thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) have become indispensable multifunctional systems for hot-section component protection. This review systematically delineates the evolutionary trajectory of TBC/EBC systems, transitioning from traditional yttria-stabilized zirconia (YSZ) and simple silicates to advanced multi-rare-earth-doped oxides, A₂B₂O₇ pyrochlore structures, and high-entropy ceramic systems. A critical comparative assessment is provided regarding their phase stability, thermal-physical properties, and durability challenges above 1200 °C. Furthermore, this paper provides an in-depth analysis of high-temperature degradation mechanisms, focusing on the thermochemical and thermomechanical interactions under calcium-magnesium-alumino-silicate (CMAS) attack, water-oxygen corrosion, and molten salt infiltration. By synthesizing current research gaps, we highlight the trade-offs between low thermal conductivity, high toughness, and environmental resistance. Finally, a strategic roadmap for next-generation coatings is proposed, emphasizing the integration of high-entropy material design, multi-scale structural optimization, and AI-driven life prediction models to meet the stringent reliability requirements of future propulsion systems. Full article

Thermal barrier coatings (TBCs) require materials with intrinsically low thermal conductivity and high grain-boundary thermal resistance to maximize the temperature gradient across the top coat. In this work, the effective thermal conductivity of more than 40 prospective TBC oxides belonging to seven structural families (YSZ/YSH, pyrochlores/fluorites A₂B₂O₇, defective fluorites A₃BO₇, fergusonite/monazite ABO₄, and perovskites ABO₃) was systematically deconvoluted into intrinsic grain thermal conductivity (k_grain) and grain-boundary (R_gb) contributions. It is shown that grain-boundary Kapitza resistance dominates heat transport in virtually all advanced oxides, contributing 60–90% to the total thermal resistance of polycrystalline samples. The lowest k_grain values (4–12 W m⁻¹ K⁻¹) are found for cerates and certain tantalates, while the highest R_gb (up to 7.2 × 10⁻⁶ m² K W⁻¹) are characteristic of high-entropy and heavily doped perovskites. Orthorhombically distorted SrCeO₃-based and high-entropy perovskites combine moderate k_grain (4.7–27.9 W m⁻¹ K⁻¹), high R_gb, and tunable thermal-expansion coefficients (10–13 × 10⁻⁶ K⁻¹), making them the most promising candidates for next-generation TBCs. These findings provide a rational basis for microstructure engineering and composition design aimed at maximizing the temperature drop across TBC layers while maintaining phase stability and CMAS resistance. Full article

Residual grit particles introduced during grit blasting are important process-induced defects that can significantly affect the interfacial damage evolution of thermal barrier coatings (TBCs) under thermal cycling; however, the coupled effects of thermally grown oxide (TGO) amplitude, grit size, and grit position on crack propagation in the bond coat (BC) remain insufficiently understood. In this work, a two-dimensional finite element model containing residual alumina grit particles was established to investigate the influence of these three factors on the radial stress distribution and crack growth behavior in the BC, and their individual contributions and interaction effects were further quantified using response surface methodology. The results showed that TGO morphology and interfacial grit defects jointly controlled the stress concentration and crack propagation behavior in the BC. Increasing the TGO amplitude intensified the radial tensile stress concentration in the BC and gradually shifted the critical stress region during thermal cycling. Larger grit particles further aggravated the local stress concentration near the grit tips, while the movement of grit particles toward the TGO peak led to a more pronounced increase in stress concentration and crack propagation tendency. The crack growth behavior was found to be consistent with the corresponding stress evolution characteristics. Response surface analysis further revealed that grit size and grit position had much stronger effects on crack propagation than TGO amplitude, and their interaction was the most significant among all factor combinations. The minimum crack length in the BC layer was obtained at a TGO amplitude of 0.01 mm, a grit size of 20 μm, and a position parameter of 0.752, and the predicted value agreed well with the finite element result. This study provides a comparative basis for interfacial damage assessment and grit-blasting parameter optimization in TBCs containing residual grit defects. Full article

This study investigates how processing parameters and powder characteristics influence the mechanical performance of thermal barrier coatings (TBCs) applied to a Ti-6Al-4V alloy. Two TBCs were deposited by Atmospheric Plasma Spray (APS) using different processing conditions, feedstock characteristics, and coating thicknesses (thin and thick configurations). TBC characterization included powder size analysis, scanning electron microscopy (SEM), surface roughness, X-ray diffraction, instrumented indentation, and scratch testing. Mechanical behavior was assessed using creep testing at 125 MPa and 500 °C for coated and uncoated samples. Fracture surfaces of crept samples were analyzed by SEM and stereomicroscopy. Thicker TBC exhibited higher elastic modulus but contained microcracks and higher porosity, resulting in a higher steady-state creep rate (0.0006 h⁻¹, approximately 167% above the uncoated substrate) and reduced rupture time. Conversely, thinner TBC remained initially crack-free, promoting stress redistribution and leading to a lower creep rate (0.0002 h⁻¹, about 67% below the substrate) and delayed failure. Fractographic analysis revealed ductile fracture of Ti-6Al-4V in all conditions, indicating that coatings influenced damage accumulation rather than fracture mode. These findings underscore the combined effect of processing parameters and coating architecture on TBC performance for aerospace applications. Full article

To simulate the erosion damage behavior of thermal barrier coatings (TBCs) under actual service conditions in an aircraft engine environment, this study developed a multi-factor coupled test setup capable of simulating combined loading under high-temperature (1150 °C), high-speed (0.4 Mach), and solid-particle erosion conditions. Yttria-stabilized zirconia (YSZ) TBCs were prepared using electron beam physical vapor deposition (EB-PVD). For different erosion durations (2 h, 5 h, 8 h, 12 h), the evolution of macroscopic and microscopic morphologies as well as the development of residual stresses in the thermally grown oxide (TGO) layer were systematically investigated. The results indicate that the erosion process of the YSZ coating can be divided into three stages. During the initial high-erosion-rate stage (8.17 g/kg), erosion damage was confined to the grain tips of the columnar crystals, primarily caused by brittle fracture at the grain tips, and the TGO stress was relatively low (−0.6 GPa). During the intermediate stage, the erosion rate was lower (2.74 g/kg). Impact stresses induced microcracks within the columnar grains, which gradually connected to form intergranular fractures. This led to the expansion of localized spalling pits. The interface began to wrinkle, and the stress rose to −2.2 GPa. In the final accelerated failure stage (5.88 g/kg), horizontal cracks fully propagated, leading to large-scale peeling of the coating. The stress was released to −0.9 GPa. The coating failure mechanism evolves from surface damage to interfacial peeling, which is closely related to the coating structure, stress evolution, and interfacial state. Full article