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In the present work, we used a hybrid ceramic fabrication technology to synthesize lead zirconate titanate (PZT) piezoelectric ceramics coated with yttrium oxide–stabilized zirconia (YSZ) powders (PZT@YSZ). The tailoring effects of the YSZ grain coating layer were investigated systematically. The results demonstrate that the mechanical properties of the modified PZT ceramics were successfully improved, which is mainly attributed to the synergistic effect of reinforced martensitic transformation toughening, micro-crack toughening, and second-phase dispersion toughening of the YSZ grain coating layer. More importantly, the piezoelectric properties of the PZT@YSZ ceramics, such as d33, kp, strain (S), strain hysteresis Hs, and d33*, have no declined, instead, have improved significantly. This is due to the coexistence of the rhombohedral-tetragonal phase of PZT in the PZT@YSZ ceramics, which is confirmed by Rietveld refinements in X-ray diffraction. Furthermore, the breakdown strength of the PZT@YSZ ceramics increased by 28%, a result of the reduction in grain size. This work describes an effective approach to simultaneously toughening PZT-based piezoelectric ceramics and enhancing their piezoelectric properties.

In this study, Inconel 718 coatings were deposited by the high-pressure cold spray technique, and post-process solution and double aging treatments were conducted. The microstructures of the as-deposited and heat-treated IN718 were analyzed, and their mechanical properties were tested. It was found that the micro-dendritic structures in the original powder were severely elongated in the as-deposited IN718 coating due to plastic deformation during the cold spray process. After solution heat treatment, Nb, Mo, and Ti-rich segregations could be dissolved, transforming to MC carbide and a needle-like δ phase. It was found that the needle-like δ phase at the grain boundary had a pinning effect to slow down the grain growth. In addition, strengthening phases could be formed by aging treatments. The mechanical properties of the cold sprayed Inconel 718 could be improved by proper solution and aging heat treatments.

Microstructures of yttria-stabilized zirconia (YSZ) atmospheric-plasma-sprayed (APS) thermal barrier coatings (TBCs) and their terahertz dielectric properties were investigated to quantitatively determine porosities by effective medium theory (EMT). Various samples with different porosities ranged from 9.15% to 21.58% were prepared by different particle size powders and spray power. Both the theoretical and experimental results showed that the interferential oscillation period of reflectance spectra of APS YSZ TBCs samples depends on optical thickness of ceramic coatings, and optical thickness depends on permittivity for known geometric thickness. The real part of permittivity ϵ ′ decreased as the porosity increased, the depolarization factor ζ of APS YSZ TBCs pores, which was estimated by comparing the experimental value with the simulated value obtained by the Maxwell–Garnett EMT model and Bruggeman EMT model, approached to a fixed value, owing to the typical lamellar structure of APS-TBCs, and was 0.7 and 0.6 in respective models. Samples of 185–459 μ m thickness verified that the technique varied from scanning electron microscope statistics results by

In this study, a newly-tailored plasma-sprayed (PS) yttria-stabilized zirconia (YSZ) ceramic coating towards enhanced strain tolerance and sintering resistance was developed to improve the durability of TBCs. The thermal shock life was found to be markedly prolonged by more than four times. Failure mechanisms and sintering behavior of the newly-structured and conventional TBCs were systematically investigated through microstructural and mechanical analyses. Conventional TBCs suffered a premature spallation due to rapid sintering-induced stiffening of the ceramic top coat. In contrast, the new coating exhibits an enhanced sintering resistance whereby preserving a good strain tolerance over time. Specifically, its elastic modulus after thermal exposure remains comparable to the as-sprayed states. The effect of ceramic top coat stiffness on cracking behavior of TBCs was clarified by a corresponding cohesive zone finite element modeling. This study provides a new option for improving TBCs durability and the results could benefit the increased integrity of TBCs.

The flight forbidden area (FFA) in convective weather is an important information resource for aviation. Using the density-based spatial clustering of applications with noise (DBSCAN), convex hull function in OpenCV library and other methods, the generation and verification of FFA in convective weather based on real weather and trajectory data are proposed in this study. Four relationship classes between flight trajectories and FFA are defined and eight examples are conducted to investigate the impact of radar reflectivity threshold and safety margin on the accuracy of FFA. Judging from the results, 40 dBZ is a better radar reflectivity threshold for the generation of FFA in convective weather, as the proportion of samples that fly outside of FFA with 40 dBZ is higher than that with 35 dBZ, and the proportion of samples that fly inside of FFA with 40 dBZ is lower than that with 35 dBZ. In addition, the accuracy of FFA decreases rapidly with the increasing of safety margin and it is suggested that the safety margin should range from 7 to 15 km to get a more realistic FFA.

Because gas turbine engines must operate under increasingly harsh conditions, the degradation of thermal barrier coatings (TBCs) by calcium-magnesium-alumina-silicate (CMAS) is becoming an urgent issue. Mullite (3Al2O3·2SiO2) is considered a potential material for CMAS resistance; however, the performance of mullite in the presence of CMAS is still unclear. In this study, mullite and Al2O3–SiO2 were premixed with yttria stabilized zirconia (YSZ) in different proportions, respectively. Porous ceramic pellets were used to conduct CMAS hot corrosion tests, and the penetration of molten CMAS and its mechanism were investigated. The thermal and mechanical properties of the samples were also characterized. It was found that the introduction of mullite and Al2O3–SiO2 mitigated the penetration of molten CMAS into the pellets owing to the formation of anorthite, especially at 45 wt% mullite/55 wt% YSZ. Compared with Al2O3–SiO2, mullite possesses a higher chemical activity and undergoes a faster reaction with CMAS, thus forming a sealing layer in a short time. Additionally, the thermal expansion coefficient, thermal conductivity, and fracture toughness of different samples were considered to guide the architectural design. Considering the CMAS corrosion resistance, thermal and mechanical performance of TBCs systematically, a TBC system with a multilayer architecture is proposed to provide a theoretical and practical basis for the design and optimization of the TBC microstructure.

The analysis of a failed elbow in a methanol synthesis tower is presented in this work. In order to examine the causes of failure, various techniques including visual inspection, optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy and a tensile test were carried out. The investigation results suggested that failure occurred due to stress corrosion cracking. The low content of molybdenum in this failed tube caused the decrease in pitting corrosion resistance. At the same time, an intergranular corrosion morphology was present in the inner wall of the tube, which was mainly caused by the sulfur present in the scale layer. Chlorine was also detected in the cracks. Moreover, the residual stress was inevitable in the vicinity of the weld due to the repair welding. In addition, the tensile test showed that the elongation of the material was lower than the relevant standards. Therefore, premature cracks initiated in the inner wall of the elbow, and then propagated along the thickness direction and also along the circumferential direction that led to final failure under the combined action of the above factors.

In this study, a new pore structure control method for plasma-sprayed thermal barrier coatings (TBCs) through the addition of unmelted, porous yttria-stabilized zirconia (YSZ) particles was investigated. Through a unique way of feeding powder, two powder feeders were used simultaneously at different positions of the plasma flame to deposit a composite structure coating in which a conventional plasma-sprayed coating was used as a matrix and unmelted micro-agglomerated YSZ particles were dispersed in the dense conventional coating matrix as second-phase particles. The effects of the distribution and content of second-phase particles on the microstructure, mechanical properties, and lifetime were explored in a furnace cyclic test (24 h) of the composite coating. The mechanical properties and lifetime of the composite coating depend on the content and morphology of the particles embedded in the coating. The lifetime of the composite structure coatings is significantly higher than that of the conventional coatings. By adjusting the spraying parameters, the lifetime of the composite coating prepared under the optimum process is up to 145 days, which is about three times that of the conventional coating. The results of this study provide guidance for the preparation of high-performance composite structure TBCs.

Thermal barrier coatings (TBCs) are usually subjected to the combined action of compressive stress, tensile stress, and bending shear stress, resulting in the interfacial delamination of TBCs, and finally causing the ceramic top coat to peel off. Hence, it is vital to detect the early-stage subcritical delamination cracks. In this study, a novel hybrid artificial neural network combined with the terahertz nondestructive technology was presented to predict the thickness of interface delamination in the early stage. The finite difference time domain (FDTD) algorithm was used to obtain the raw terahertz time-domain signals of 32 TBCs samples with various thicknesses of interface delamination, not only that, the influence of roughness and the thickness of the ceramic top layer were considered comprehensively when modeling. The stationary wavelet transform (SWT) and principal component analysis (PCA) methods were employed to extract the signal features and reduce the data dimensions before modeling, to make the cumulative contribution rate reach 100%, the first 31 components of the SWT detail data was used as the input data during modeling. Finally, a back propagation (BP) neural network method optimized by the genetic algorithm (GA-BP) was proposed to set up the interface delamination thickness prediction model. As a result, the root correlation coefficient R2 reached over 0.95, the various errors&mdash, including the mean square error, mean squared percentage error, and mean absolute percentage error&mdash, were less than or equal to 0.53. All these indicators proved that the trained hybrid SWT-PCA-GA-BP model had excellent prediction performance and high accuracy. Finally, this work proposed a novel and convenient interface delamination evaluation method that could also be potentially utilized to evaluate the structural integrity of TBCs.

Lead zirconate titanate ceramics, Pb(ZrxTi1-x)O3 (PZT), as the backbone material of piezoelectric enterprises can be effectively modified by yttria-stabilized zirconia (YSZ) using conventional solid-state sintering technology same as the former PZT ceramics. Experimental results showed that the mechanical strength and fracture toughness of PZT piezoelectric ceramics can be much improved by 43% and 21% respectively. More importantly, the reduction tendency of the major piezoelectric properties can be suppressed substantially. The piezoelectric coefficient d33 of the YSZ-modified PZT ceramic was barely changed and the electromechanical coupling coefficient kp remained high.

Rare-earth element doping has been extensively employed as one of the effective methods to enhance the durability of thermal barrier coatings (TBCs). In present study, ytterbia and yttria co-stabilized zirconia (YbYSZ) coatings and corresponding double-ceramic-layer (DCL) coatings comprised of a dense layer were produced by atmospheric plasma spraying. And the service capability including phase stability, thermal shock behavior and CMAS resistance were systemically evaluated. After heat treatment at 1500 °C for various durations, less monoclinic phase can be found in YbYSZ specimen, indicating excellent phase stability at high temperature. In the thermal shock test, the conventional YbYSZ coatings show a longest thermal shock lifetime, which increases by ~10% as compared with that of conventional yttria-stabilized ZrO2 (YSZ) coatings. CMAS corrosion resistance of DCL coatings was studied using an isothermal corrosion test at 1300 °C. The results show that YbYSZ systems with a dense layer performed a high resistibility to CMAS corrosion, and less damage can be observed in coatings as well as smaller infiltration depth within the same time.

Currently molten silicate deposition in thermal barrier coatings application is an ongoing challenge for material scientists. To some extent, it has already been the greatest weakness of traditional yttria partially stabilized zirconia material. Thus new material candidates and strategies that can mitigate calcium‑magnesium-alumina-silicate corrosion are urgently needed. To this end, a ‘model’ experiment involving high-temperature interactions between Yb2O3-Y2O3 co-stabilized ZrO2 ceramic powders and CMAS glass was conducted in this study. This study proposes a simple but effective methodology for comparing the transport behavior of Yb3+ and Y3+ during the interaction which provides further understanding of the anti-corrosion mechanism. After exposure at 1300 °C for various durations, less degradation was observed in YbYSZ samples. Further analyses ascribed the enhancement of CMAS-mitigating capability to the low diffusion rate of Yb3+, which was highly beneficial for maintaining the microstructure and phase stability. Additionally, the potential of YbYSZ as a CMAS-resistant material for TBCs was supported by the dramatically improved thermo-physical and mechanical properties of YbYSZ compared to those of conventional YSZ.

In Air Traffic Flow Management (ATFM), one key issue is to determine the Calculated Take Off Time (CTOT) for each flight. Due to the limited slot time resources, one single flight’s slot decision could be influenced by plenty of other flights. Few existing approaches in the previous literatures consider the interaction among various flights, so that the possible solution achieved will perform low stability and performance, especially under the condition of multiple measures. Aiming to solve the resource and flights coupling problems, in this paper, we present one heuristic method based on multi-dimension flight priority, with novel proposed methods of slot division and flight ranking. Meanwhile, in order to improve the optimality and flexibility of solutions, Estimation of Distribution Algorithm (EDA) is adopted. As one meta-heuristic algorithm, EDA is used to optimize the assignment sequence based on probability model, by which to provide an enhanced approach to solve slot allocation optimization problems. The numerical experiments have been conducted, the comparison results show that our approach has high calculation performance compared with conventional meta-heuristic algorithm-based approach, and better stability and applicability for re-allocation under the dynamic situation.

In this study, corrosion behavior of Yb2O3-Y2O3 co-stabilized ZrO2 (YbYSZ) was systematically investigated under CMAS melt attack. The result was found that YbYSZ exhibited a better CMAS resistance than yttria stabilized zirconia (YSZ), which was attributed to the excellent phase stability. The degradation of grain caused by CMAS attack was greatly related to the diffusion rate of element substantially. Yb3+ exhibited a low diffusion rate contributing to good phase stability during corrosion. A corresponding first-principles calculation further confirmed this conclusion. Besides, YbYSZ showed a higher thermal expansion coefficient and lower thermal conductivity as compared with YSZ counterpart.

Structural health monitoring of multilayer thermal barrier coatings (TBCs) is very vital to ensure the structural integrity and service performance of the hot-section components of the aero-engine. In this paper, we theoretically and numerically demonstrated that the terahertz time domain spectrum and the terahertz reflectance spectrum could be adopted to estimate the structure parameters, based on the finite difference time domain (FDTD) algorithm, 64 samples which were imported with three kinds of 64 sets structure parameters had been calculated to obtain the time domain and terahertz reflectance signals. To mimic the actual test signals, the original FDTD simulation signals were processed by adding the Gaussian white noise and wavelet noise reduction. To reduce the data dimension and improve the calculation efficiency during modeling, the principal component analysis (PCA) algorithm was adopted to reduce the dimensions of time-domain data and reflectance data. Finally, these data after multiple signal processing and PCA feature extraction were used to train the extreme learning machine (ELM), combining the genetic algorithm (GA) could optimize the PCA-ELM model and further improve the prediction performance of the hybrid model. Our proposed novel and efficient terahertz nondestructive technology combined with the hybrid machine learning approaches provides great potential applications on the multilayer TBCs structural integrity evaluation.

A double-ceramic-layer (DCL) plasma-sprayed YSZ coating comprised of a mullite-YSZ protective layer towards suppressing CMAS attack was prepared in this study. The resistance of DCL coating to molten CMAS at 1300 °C was systematically investigated through phase structure as well as microstructural analysis. It was clearly revealed that the DCL coating exhibited an enhanced CMAS resistance owing to the formation of CaAl2Si2O8 layer. After 4 hours of exposure, YSZ coatings have been significantly penetrated (at least 250 μm), whereas correspondingly no CMAS was found in DCL coatings; the penetration depth in DCL coatings increased to approximately 100 μm as the duration last up to 12 h. In addition, the DCL coating performed a larger contact angle than that of YSZ coatings within the same time, promoting the resistance to CMAS.

A novel approach was presented to characterize microstructural features of thermal barrier coatings (TBCs) using terahertz spectroscopy based on machine learning algorithms. In this study, the microstructures of yttria-stabilized zirconia (YSZ) atmospheric-plasma-sprayed (APS) thermal barrier coatings were regulated by choosing different kinds of spray powders, distances and power during processing. A terahertz time-domain spectroscopy system configurated transmission mode with an incidence angle of 0° was employed to estimate terahertz properties of porous YSZ ceramic coatings, including refractive index, extinction coefficient and relative time-domain broadening ratio. The variation tendency of terahertz properties of YSZ ceramic coatings with different microstructure features (porosity, pore to crack ratio, pore size) were investigated. Principal component analysis (PCA) method was adopted to reduce the dimensions of refractive index and extinction coefficient spectra data at the range of 0.6–1.4 THz and to ensure that different terahertz properties could be treated as inputs with similar weights during modeling. Three models (multiple linear regression (MLR), back-propagation (BP) neural network and support vector machine (SVM)) were set up to conduct regression analysis. As a result, according to the contribution rates of eigenvectors, the top one principal component of refractive index spectra data and the top two principal components of extinction coefficient spectra data were selected as the model inputs. The correlation coefficient comparisons showed that the characterization accuracy of PCA-SVM reached by over 95% and outperformed the other models. Finally, this study proposed that THz nondestructive technology combined with machine learning technique is efficient and feasible for microstructural features characterization and has profound implications for the structure integrity of TBCs evaluation in gas turbine blades.

The rollers used to convey steel strips in a continuous-annealing furnace were deformed after about 12 years of service, resulting in an unevenness of the rolled strips. In this study, failure causes of the furnace rollers were investigated in terms of degradation of microstructure and mechanical properties of the roller material. After a long period of high temperature service, the microstructure of the material has changed significantly. A large number of network-like carbides precipitated at the grain boundaries, and these carbides have been greatly coarsened. It was also found that a great number of σ-phase have formed on the coarsened carbides, and that the volume fraction of the σ-phase on the grain boundaries has exceeded 50%. In addition, creep cavities have been found in the grain boundaries. Especially in regions with dense grain boundaries, the cavities formed at the intersection of grain boundaries have been linked into chains, which tend to develop into cracks. The grain boundaries of the furnace roller material after service has been severely embrittled. Both tensile and impact fracture surfaces show brittle intergranular fracture characteristics. Compared to the unused material, the tensile strength and impact toughness of the failed roller decreased significantly due to the deterioration of the microstructure. Because of the degraded mechanical properties, the rollers are prone to deformation under the service loads, thus cannot guarantee the normal production of strip steels. The results of this study provide a reference for evaluating the remaining life of furnace rollers after long-term service at elevated temperatures.

In this study, yttria-stabilized zirconia (YSZ) coatings were deposited by atmospheric plasma spraying (APS) using feedstocks with two different particle sizes. The effect of particle size on the pore structure and failure mechanism of the coatings was investigated. The evolution of the pore structure of the two kinds of coatings during cyclic thermal shock test was described by quantitative metallography. The influence of pore orientation on the thermal stress of the coating system was analyzed by the finite element method. It was found that the coatings deposited using coarse particles show a high thermal shock life time. The orientation of the pores in the coatings prepared by different particle sizes was different. A structural parameter was proposed to effectively characterize the pore orientation of the coatings. Coatings prepared by coarse YSZ powder tend to form almost the same number of horizontal and vertical pores, while coatings prepared by fine powder tend to form horizontal ones parallel to the direction of the substrate. The simulation results revealed that the vertical pores can reduce the thermal stress in the coating. The results of this investigation are a benefit to the design and integrity of TBCs.

In this work, a terahertz time-domain spectroscopy (THz-TDS) system was used to measure the thickness of thermal barrier coatings (TBCs) and characterize the interface morphology of TBCs after erosion. Reflection mode, with an angle of incidence of 0, was used for inspection before and after erosion. The refractive index, thickness, and internal structure evolution tendency of the yttria-stabilized zirconia (YSZ) top coat were estimated under consideration of the interaction between the pulsed THz waves and the TBCs. The surface roughness of the top coat surface was considered for the errors analysis in the refractive index and thickness measurement. To reduce the errors introduced by the refractive index change after erosion, two mathematical models were built to assess the thickness loss. Then, the thickness loss was compared with results estimated by the micrometer inspection method. Finally, the basic erosion sample profile with Ra roughness was obtained, and the broadening of THz pulses were suggested as a possible measure for the top coat porosity change, showing that THz waves can be a novel online non-destructive and non-contact evaluation method that can be widely utilized to evaluate the integrity of TBCs applied to gas turbine blades.

Splat morphology is an important factor that influences the mechanical properties and durability of thermal barrier coatings (TBCs). In this study, yttria-stabilized zirconia (YSZ) coatings with different lamellar interface morphologies were deposited by atmospheric plasma spraying (APS) using feedstocks with different particle sizes. The influence of lamellar interface roughness on the cracking resistance of the coatings was investigated. Furthermore, the thermal shock and erosion resistance of coatings deposited by two different powders was evaluated. It was found that the particle size of the feedstock powder affects the stacking morphology of the splat that forms the coating. Coatings fabricated from coarse YSZ powders (45–60 μm) show a relatively rough inter-lamellar surface, with a roughness about 3 times greater than those faricated from fine powders (15–25 μm). Coatings prepared with fine powders tend to form large cracks parallel to the substrate direction under indentation, while no cracking phenomena were found in coatings prepared with coarse powders. Due to the higher cracking resistance, coatings prepared with coarse powders show better thermal shock and erosion resistances than those with fine powders. The results of this study provide a reference for the design and optimization of the microstructure of TBCs.