Search Results (266)

Improving the energy efficiency of advanced ultra-supercritical (USC) power plants by increasing steam operating temperature up to 700 °C can be achieved, at reduced cost, by using novel engineering design concepts, such as coated steam pipe systems manufactured from high temperature materials commonly used in current operational power plants. The durability of thermal barrier coatings (TBC) in advanced USC coal power systems is critically influenced by thermally grown oxide (TGO) evolution and interfacial stress under thermo-chemo-mechanical coupling. This study investigates a novel dual-pipe coating system comprising an inner P91 steel pipe with dual coatings and external cooling, designed to mitigate thermal mismatch stresses while operating at 700 °C. A finite element framework integrating thermo-chemo-mechanical coupling theory is developed to analyze TGO growth kinetics, oxygen diffusion, and interfacial stress evolution. Results reveal significant thermal gradients across the coating, reducing the inner pipe surface temperature to 560 °C under steady-state conditions. Oxygen diffusion and interfacial curvature drive non-uniform TGO thickening, with peak regions exhibiting 23% greater thickness than troughs after 500 h of oxidation. Stress analysis identifies axial stress dominance at top coat/TGO and TGO/bond coat interfaces, increasing from 570 MPa to 850 MPa due to constrained volumetric changes and incompatible growth strains. The parabolic TGO growth kinetics and stress redistribution mechanisms underscore the critical role of thermo-chemo-mechanical interactions in interfacial degradation. These research findings will facilitate the optimization of coating architectures and the enhancement of structural integrity in high-temperature energy systems. Meanwhile, clarifying the stress evolution within the coating can improve the ability to predict failures in USC coal power technology. Full article

Performance breakthroughs and safety assurance of aerospace equipment are critical to the advancement of modern aerospace technology. As a key protective system for the hot-end components of aeroengines, thermal barrier coatings (TBCs) play a vital role in ensuring the safe operation of aeroengines and overall flight safety. To address the core detection technology challenge for micro–nano damage precursors in aerospace TBCs, this study proposes an enhanced detection framework, namely YOLOv11-LADC. Specifically, the framework integrates the LSKA attention mechanism to construct the C2PSA-LA module, thereby enhancing the detection capability for micro–nano damage precursors and adaptability to complex small-sample datasets. Additionally, it introduces deformable convolutions (DeformConv) to build the C3k2-DeformCSP module, which dynamically adapts to the irregular deformations of micro–nano damage precursors while reducing computational complexity. A data augmentation strategy incorporating 19 transformations is employed to expand the dataset to 5140 images. A series of experimental results demonstrates that, compared with the YOLOv11 baseline model, the proposed model achieves a 1.6% improvement in precision (P) and a 2.0% increase in recall (R), while maintaining mAP50 and mAP50-95 at near-constant levels. Meanwhile, the computational complexity (GFLOPs) is reduced to 6.2, validating the superiority of the enhanced framework in terms of detection accuracy and training efficiency. This further confirms the feasibility and practicality of the YOLOv11-LADC algorithm for detecting multi-scale micro–nano damage precursors in aerospace TBCs. Overall, this study provides an effective solution for the intelligent, high-precision, and real-time detection of multi-scale micro–nano damage precursors in aerospace TBCs. Full article

In many industrial applications, engine, turbine, and rotor components are coated with thin layers that protect them from corrosion, high temperatures, or pressure. This paper presents a fast and effective method for testing such protective coatings. For this purpose, an eddy current probe consisting of a single coil was designed and constructed. The high sensitivity of the probe was achieved by using a pot core, which significantly reduced magnetic flux losses. In addition to the substrate, the test samples also contained carbide coatings or thermal barrier coatings (TBCs), which were sprayed with an Axial III triple-plasma torch or a single-electrode torch. The use of different process parameters made it possible to obtain coatings of varying thickness, which were determined using a scanning electron microscope (SEM). Measurements of the probe impedance components were performed in the frequency range from 500 Hz to 50 kHz. In all cases, based on the analysis of changes in resistance and reactance, it was possible to distinguish each of the tested samples. Even slight changes in thickness of only 9 μm caused significant changes in probe impedance, enabling effective testing of carbide coatings and TBCs. Full article

Ions of Gd³⁺ and Yb³⁺ have radii similar to those of Zr⁴⁺, enabling them to form limited solid solutions in the ZrO₂ lattice through substitution. After solid solution formation, oxygen vacancy defects and complex defect aggregates are generated, which are crucial for stabilizing the high-temperature phase structure and reducing thermal conductivity. Therefore, in this study, 8 wt% Y₂O₃ and 5 wt% Yb₂O₃ were doped with 5 wt%, 10 wt%, and 15 wt% Gd₂O₃, respectively, to stabilize zirconia powders. GYYZO thermal barrier coatings (TBCs) were fabricated via atmospheric plasma spraying (APS). Subsequently, the GYYZO coatings with different Gd₂O₃ addition amounts were subjected to continuous thermal shock cycling at 1100 °C for 10, 30, 60, 90, and 150 cycles. The results indicate that the incorporation of Gd₂O₃, Yb₂O₃, and Y₂O₃ leads to the formation of stable tetragonal ZrO₂ phase in the GYYZO coatings. Although increasing the Gd₂O₃ addition amount reduces the thermal conductivity of the coatings, excessive Gd₂O₃ addition causes coating spallation. The GYYZO coating with 10 wt% Gd₂O₃ exhibits the lowest thermal conductivity of 0.59 W/(m·K). Additionally, the GYYZO coating with 10 wt% Gd₂O₃ can withstand thermal cycling for 150 cycles, while the one with 5 wt% Gd₂O₃ can endure 90 of thermal cycles. In contrast, the 8YSZ coating cracks and spalls after 60 thermal cycles. These findings demonstrate that doping ZrO₂ with Gd₂O₃, Yb₂O₃, and Y₂O₃ can enhance the thermal cycling resistance of the coatings and effectively reduce their thermal conductivity, but excessive Gd₂O₃ addition will decrease the coating adhesion strength. Full article

Based on a realistic three-dimensional geometric model, this study numerically investigates the influence of yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) on the aerothermal performance of an annular combustor by employing a conjugate heat transfer (CHT) and non-premixed reactive flow coupling approach. Considering the inner and outer liners, double-wall exhaust bends, and the full configuration of cooling holes, two cases—with and without the TBCs—were analyzed. The results reveal that the application of TBCs markedly modifies the near-wall flow structures and heat transfer characteristics. The cooling air mass flow rate decreases from 0.1211 kg/s to 0.1023 kg/s, corresponding to a 15.5% reduction in cooling load. The main recirculation zone becomes more compact, with enhanced vortex intensity, smoother velocity distribution, and improved flame stability. The high-temperature core region extends further downstream, and the peak temperature increases by approximately 80–100 K, indicating more complete combustion and greater heat retention. The outlet temperature distribution factor (OTDF) decreases from 57.34% to 44.48%, leading to a 22.4% improvement in temperature uniformity. The average wall temperatures of the inner liner, outer liner, and exhaust bend decrease by 3.7%, 8.8%, and 7.5%, respectively, with local peak reductions exceeding 250 K. The study demonstrates that the YSZ TBCs enhances the combustor’s thermal protection capability, flow stability, and temperature uniformity through a coupled mechanism of “thermal insulation–flow reconstruction–energy redistribution.” It should be noted that this study considers only the effect of the ceramic top coat of the TBCs, excluding the metallic bond coat and the thermally grown oxide (TGO) layer. Full article

Thermal barrier coatings (TBCs) are critical for protecting hot-section components in gas turbines and aero-engines. Traditional yttria-stabilized zirconia (YSZ) coatings are prone to phase transformation and sintering-induced failure at elevated temperatures. This study fabricated CeScYSZ (4 mol% CeO₂ and 6 mol% Sc₂O₃ co-doped YSZ)/NiCrAlY TBCs using atmospheric plasma spraying (APS). A five-factor, four-level orthogonal experimental design was employed to optimize spraying parameters, investigating the influence of powder feed rate, spray distance, current, hydrogen flow rate and primary gas flow rate on the coating’s microstructure and mechanical properties. The resistance to calcium–magnesium–alumino–silicate (CMAS) corrosion was compared between CeScYSZ and YSZ coatings. The results indicate that the optimal parameters are a spray distance of 100 mm, current of 500 A, argon flow rate of 30 L/min, hydrogen flow rate of 6 L/min, and powder feed rate of 45 g/min. Coatings produced under these conditions exhibited moderate porosity and excellent bonding strength. After exposure to CMAS corrosion at 1300 °C for 2 h, the CeScYSZ coating demonstrated significantly superior corrosion resistance compared to YSZ. This enhancement is attributed to the formation of a CaZrO₃ physical barrier and the synergistic effect of Ce and Sc in suppressing deleterious phase transformations. This study provides an experimental basis for the preparation and application of high-performance TBCs. Full article

Growth kinetics and the irreversible deformation of thermally growth oxide (TGO) critically affect the delamination and cracking at the interface of thermal barrier coatings (TBCs). In this study, TGO dynamic growth during furnace cycles is simulated using three different approaches. The stress evolution and damage characteristics near the interface are compared in various TGO growth modes. Furthermore, the influences of TGO creep at high temperatures on the interface delamination and coating failure are also investigated. The results reveal that TGO growth achieved through material transformation (growth mode III) leads to earlier interface delamination compared to element swelling methods (growth mode I and II). Although the stress value in growth mode II is higher than that in growth mode I after all cycles, earlier delamination and spallation occur in mode I due to faster stress accumulation in the initial stage of thermal cycle. Moreover, rapid TGO creep is found to reduce the accumulated stress within the ceramic layer and delay the onset of interface delamination. These findings provide important theoretical insights for the development and life assessment of advanced TBCs. Full article

To meet gas turbines’ growing demand for high-performance thermal barrier coatings (TBCs), this study addresses the limitations of traditional single-layer 8% Y₂O₃-stabilized ZrO₂ (YSZ) coatings in high-temperature corrosive environments. Atmospheric plasma spraying (APS) was used to fabricate the double-ceramic TBCs with (Sm_0.2Gd_0.2Dy_0.2Er_0.2Yb_0.2)₂(Zr_0.7Hf_0.3)₂O₇ (RHZ) as the outer layer and YSZ as the inner layer; thermal cycling corrosion tests (1000 °C, Na₂SO₄ + V₂O₅ molten salt) were conducted to compare its performance with traditional single-layer YSZ. The results showed that the YSZ corrosion products were m-ZrO₂ and YVO₄, while RHZ/YSZ produced rare-earth vanadates, m-(Zr,Hf)O₂, and t′-(Zr,Hf)O₂, and corrosion degree was positively correlated with salt concentration (which was more impactful) and the number of cycles. Both coatings failed via molten salt penetration, thermochemical reaction, and crack-induced spallation. The corrosion mechanism between the RHZ/YSZ coating and the mixed salt can be explained based on the Lewis acid–base theory and the optical basicity. The RHZ layer on the surface of RHZ/YSZ coatings indeed hinders the penetration of corrosive molten salts into the underlying YSZ layer to some extent. Full article

Thermal barrier coatings (TBCs) extend gas-turbine blade lifetime by improving high-temperature oxidation resistance and mechanical performance. We investigated the microstructural evolution, TGO growth, and Al depletion in air-plasma-sprayed (APS) single-layer YSZ top coat over a NiCrCoAlY bond coat on Ni-based superalloy circular plates, heat treated isothermally at 850 °C and 1000 °C for 50–5000 h. Cross-sectional SEM/EDS analysis showed TGO quadratic thickening kinetics at both temperatures, reaching ~10 µm at 1000 °C/5000 h, the growth rate of which was ~5.8 times higher than at 850 °C. On top of the single-layer TGO of Al₂O₃ observed from the onset, a NiCrCo oxide layer appeared and grew from ≥500 h at 850 °C, with increasing growth rate and cracking. The layer configuration of the YSZ top coat, the TGO of Al₂O₃, and the bond coat (comprising β-NiAl and γ-NiCr) on top of GTD111, showed an Al concentration gradient in the bond coat starting at 850 °C for 250 h, which intensified with increased duration and temperature. The decrease in Al concentration in the bond coat and the growth of TGO are due to the dissolution of β-NiAl and subsequent Al diffusion to the Al₂O₃ TGO. Full article

Investigating the relationship between coating structure and thermal stress is crucial for improving the service performance of double-ceramic-layer (DCL) thermal barrier coatings (TBCs). This study systematically examines a DCL TBC comprising a Gd₂O₃-Yb₂O₃-Y₂O₃ co-doped ZrO₂ (GYYZ) top layer and Y₂O₃-stabilized ZrO₂ (YSZ) intermediate layer. Using combined finite element analysis and experimental validation, the influence of top-layer structural parameters (porosity, pore size, thickness) on thermal stress distribution under thermal shock conditions and resultant coating performance was investigated. Results indicate that coating interfaces, particularly GYYZ/YSZ and YSZ/bond coat (BC) interfaces, exhibit high sensitivity to top-layer structural parameters. Optimal GYYZ top-layer parameters were identified as: 10–15 vol.% porosity, 10–20 μm pore diameter, and ~0.15 mm thickness. Reducing the top-layer porosity from 20 vol.% to 15 vol.% increased microhardness by 12.8% and extended thermal cycling life by 87.5%. The coating failure mode shifted from the YSZ/BC interface to the GYYZ/YSZ interface, aligning with simulated thermal stress distributions. Full article

This study investigates the microstructural evolution and damage mechanisms of the nickel-based single-crystal superalloy DD9-thermal barrier coating (TBC) system under 1050 °C high-temperature oxidation, while conducting a comparative analysis of oxidation behavior with the DD6-TBC system. Results show that both systems have similar oxidation mechanisms but face long-term oxidation drawbacks: as oxidation time increases, the thermally grown oxide (TGO) evolves into a mixed oxide layer and an Al₂O₃ layer, with initial rapid TGO growth consuming Al in the bond coat (BC) and subsequent Al depletion slowing growth, though long-term TGO accumulation raises cracking and spallation risks. DD9 and DD6 substrates significantly affect substrate-BC interfacial interdiffusion: the interdiffusion zone (IDZ) and secondary reaction zone (SRZ) grow continuously (SRZ growing faster), and linear topologically close-packed (TCP) phases precipitate in the SRZ, spreading throughout the substrate and impairing high-temperature mechanical properties. Specifically, DD9’s IDZ growth rate is faster than DD6’s in the first 800 h of oxidation but slows below DD6’s afterward, reflecting DD9’s superior long-term oxidation resistance due to better temperature resistance and high-temperature stability. This study clarifies key high-temperature service disadvantages of the two systems, providing experimental support for coated turbine blade life evaluation and a theoretical basis for optimizing third-generation single-crystal superalloy-TBC systems to enhance high-temperature service stability. Full article

The application of thermal barrier coatings (TBCs) for protecting mechanical components is widespread, particularly in high-temperature environments, such as gas turbines and aero-engines. Ensuring the integrity of these coatings throughout their service life is essential, as their degradation can lead to delamination, ultimately compromising the underlying component. It has been demonstrated that monitoring the thermal diffusivity value over time allows the monitoring of degradation of the coatings. Common thermographic techniques like pulsed and lock-in thermography have been used so far. However, to enhance both the signal-to-noise ratio (SNR) and the accuracy of thermal property measurements, new active thermography techniques have been developed. These methods rely on optimized excitation schemes combined with advanced signal processing strategies. In this work, we first introduce the pulse-compression thermography approach, which employs pseudo-noise modulated excitation to monitor and estimate the thermal diffusivity of the coating layers. Full article

In this study, the effects of plasma assistance on the electron beam physical vapour deposition (EB-PVD) process were investigated using an industrial coater (Smart Coater ALD Vacuum Technologies GmbH) equipped with a dual hollow cathode system. This configuration enabled the generation of a plasma environment during the deposition of the ceramic top coat onto a metallic substrate. The objective was to assess how plasma assistance influences the microstructure and thickness distribution of 7% wt. yttria-stabilised zirconia (YSZ) thermal barrier coatings (TBCs). Coatings were deposited with and without plasma assistance to enable a direct comparison. The thickness uniformity and columnar morphology of the 7YSZ top coats were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mechanical properties of the deposited coatings were verified by the scratch test method. The results demonstrate that, in the presence of plasma, columnar grains become more uniformly spaced and exhibit sharper, well-defined boundaries even at reduced substrate temperatures. XRD analysis confirmed that plasma-assisted EB-PVD processes allow for maintaining the desired tetragonal phase of YSZ without inducing secondary phases or unwanted texture changes. These findings indicate that plasma-assisted EB-PVD can achieve desirable coating characteristics (uniform thickness and optimised columnar structure) more efficiently, offering potential advantages for high-temperature applications in aerospace and power-generation industries. Continued development of the EB-PVD process with the assistance of plasma generation could further improve deposition rates and TBC performance, underscoring the promising future of HC-assisted EB-PVD technology. Full article

Thermal barrier coating (TBC) around film-cooling holes is a key failure location for turbine blade TBC. This study built a numerical model. The model used conjugate heat transfer (CHT) and sequential thermal-stress calculation methods. It analyzed the temperature and stress fields in the TBC around film-cooling holes. The holes had different inclination angles (30°, 45°, and 60°). It also explored the balance between cooling effectiveness and stress at these angles. Results show that increasing the film-cooling hole angle reduces the cooling film coverage area significantly. Cooling effectiveness becomes worse. The temperature field near the holes is complex. Sharp temperature gradients exist there. An inverse temperature gradient appeared in the top coat (TC) layer at the hole exit. Stress in the TBC was analyzed next. Analysis was conducted under rated operating conditions. Analysis was also completed after 500 h of creep under these conditions. Stress concentration around the holes is obvious. At room temperature, Mode I cracks easily form upstream of the holes. Mode II cracks easily form downstream. Under rated conditions, mixed-mode cracks (I + II) easily form downstream. The coating experiences larger stress at room temperature. This means that the coating is more likely to spall during cooling. Increasing the hole angle can reduce stress concentration. It can also lower the chance of crack formation. However, a larger angle increases the normal momentum of the cooling jet. This reduces film coverage. Therefore, after considering both cooling effectiveness and TBC failure, the 45° film-cooling hole is optimal. Full article

Electron beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBCs) are widely used to protect the hot section parts of aircraft engine turbines due to its uniform columnar microstructure and high strain tolerance. The microstructure and thermal shock life of 7 wt% Y₂O₃ stabilized zirconia (YSZ) coatings produced by EB-PVD were investigated as a function of oxygen gas flow during deposition. The surface and cross-section microstructure of EB-PVD YSZ coatings were highly influenced by the oxygen gas flow. When the oxygen gas flow is less than 60 sccm, a sandwich is formed between the bond coat (BC) layer and the YSZ layer, which significantly reduces the thermal shock life of the coating. Full article