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• The 980 °C/300 MPa creep test results indicate that the creep lives and elongation of the three typical orientations at 980 °C are [1 1 1] orientation > [0 0 1] orientation > [0 1 1] orientation. The necking sections of [0 0 1], [0 1 1] and [1 1 1] orientation are circular and elliptical, respectively. Meanwhile, on the microscopic scale, the damage evolution caused by the expansion of the internal micropores in the single crystal alloy under the three orientations shows fourfold symmetry, double symmetry and triple symmetry. • During the creep process, fracture mechanism is related to the actuation of the slip system and the magnitude of the shear stress on the slip plane. Meanwhile, the damage evolution of nickel-based monocrystalline materials caused by the expansion of micropores is characterized by quadruple symmetry, double symmetry and triple symmetry, which is also attributed to the differences in the moving slip systems and explains the different cleavage planes of different orientations, where the creep life of the [0 1 1] oriented alloy is the shortest compared to the other orientations. • The anisotropic creep constitutive model and damage model based on the crystal plasticity theory can effectively reflect the difference in the creep deformation and damage evolution of a single crystal with different orientations. The simulation results are in agreement with the experimental results, which show that the theory can reflect the anisotropy of the characteristics of single crystal materials. Due to the anisotropy of the modulus of face-centered cubic cells, the nickel-based single crystal alloys exhibits substantial anisotropy at high temperatures. Their creep properties, especially the creep rupture lives, are related to the actuation of the slip system and the magnitude of the shear stress on the slip plane. The creep orientation sensitivity has been analyzed through creep experiments, as well as the microstructure and morphology of the fracture. On the macroscale, the necking sections of [0 0 1], [0 1 1] and [1 1 1] orientations are circular, elliptical and circular, respectively. Meanwhile, on the microscopic scale, the damage evolution caused by the expansion of the internal micropores in the single crystal alloy under the three orientations shows fourfold symmetry, double symmetry and triple symmetry, respectively. Based on the crystal plasticity theory, an anisotropic creep constitutive model and damage model are established to reflect the difference in creep deformation and damage evolution caused by orientation. The numerical simulations of the whole creep process of a second generation nickel-based single crystal superalloy show that the creep constitutive model and damage model can simulate the deformation and damage of the specimen under different orientations, and the creep life can be obtained. [ABSTRACT FROM AUTHOR]

The development of photocatalytic nano-purifiers with high electrons and holes separation efficiency and high-photocatalytic activity is essential in treating water and air pollution. In this paper, novel nano-purifiers with S-scheme faceted heterojunction created between BiOCl nanosheets (110) facets and TiO 2 hollow nanocubes (001) facets were successfully fabricated. In nano-purifiers, BiOCl nanosheets are enriched with oxygen vacancies capable of trapping electrons, which synergize with the unique S-scheme faceted heterojunction charge transfer mechanism to facilitate carrier separation and migration to a large extent. Herein, BiOCl(110) nanosheets/TiO 2 (001) hollow nanocubes nano-purifiers (BTHNs) were significantly enhanced in photocatalytic treatment of water and air pollution and were not inferior to other cleaning agents. The obtained 15BTHNs showed the best photocatalytic purification ability among the same series of products. 15BTHNs could degrade 99.9% of RhB in 70 min, which was 25 times higher than that of pure THNs, and effectively removed 44.8% of NO. Moreover, the reduction rate of Cr (Ⅵ) for 15BTHNs reached 99.9% in 90 min, with a kinetic constant 21.5 times higher than that of pure THNs. Active species trapping experiments revealed that four active species of BTHNs contributed to the RhB oxidation reaction in the following order:·OH>h+>·O 2 ->e-, and the contribution rates of 15BTHNs were 45.0%, 38.0%, 12.3%, and 4.7%, respectively. The appropriate ratios of oxidizing TiO 2 to reducing BiOCl in 15BTHNs allowed the generated active species to be fully utilized, achieving oxidation-reduction equilibrium as well as improving the photocatalytic efficiency. This work reveals that the S-scheme faceted heterojunction formed in the BiOCl/TiO 2 nano-purifier was a progressing approach for water and air cleaning. [Display omitted] • A novel nano-purifier was designed by coupling BiOCl nanosheets with rich O vacancies to TiO 2 hollow nanocubes. • An S-scheme faceted heterojunction was formed between TiO 2 (001) facets and BiOCl (110) facets. • 15BTHNs demonstrated superb oxidation-reduction bifunctional purification capability in both water and air treatment. • ·OH and h+ are the main active species in the photocatalytic oxidation reaction of the nano-purifiers. • This work sheds new light on the correlation between O vacancies, faceted modification, and S-scheme heterojunction. [ABSTRACT FROM AUTHOR]

• The characteristics of microstructure with different casting processes are described. • The tests are carried out on specimens cutting from blades instead of standard specimens. • The models of the grains have been established, inter-grain interaction has been analyzed. • Viscoplastic constitutive equation has been established considering the microstructure characteristics. • The prediction of K480 creep lives with different microstructures has been realized. Creep experiments were performed on miniature K480 nickel-based superalloy specimens at 835 °C and 400 MPa. These specimens were cut from turbine blades processed with different casting processes and pouring temperatures. The microstructure analysis, fracture morphology analysis, and grain size analysis were carried out by scanning electron microscopy (SEM), indicating that the influence of the moulding process and pouring temperature on the microstructure of the alloy is mainly reflected in the difference in the size of crystal grains, grain boundary precipitates and casting defects, which in turn affects the high temperature creep properties of the alloy. Based on crystal plasticity theory, a polycrystalline alloy viscoplastic constitutive equation considering the moulding process and pouring temperature parameters is established, meanwhile, the geometric models of the K480 alloy were established based on the observations of its microscopic structure under SEM. The study revealed the relationship between the casting process of the blade, the microstructure of the material, and the creep property of the specimen. The established plastic constitutive model can predict blade stress rupture life under different casting processes. [ABSTRACT FROM AUTHOR]

• Investigated the influence of sliver defects on the creep rupture life of nickel-based single crystal superalloys. • Revealed the damage mechanism of sliver defects on the creep life of single crystal superalloys through SEM and EBSD observations. • Developed creep constitutive equations for specimens containing sliver based on crystal plasticity theory, explaining the reasons for the decrease in sample life caused by sliver. • Predicted the damage tolerance of sliver defects with different orientations. Sliver defects are common casting imperfections in the preparation of single crystal blades, significantly impacting the high-temperature mechanical performance of blades and potentially leading to blade failure. A detailed study was conducted on the microstructure of sliver in the second-generation nickel-based single crystal superalloy CMSX-4, focusing on its influence on creep performance at 980 °C/250 MPa. Results indicate a substantial impact of sliver on the creep performance of single crystal superalloys, with a 26.37 % reduction in creep rupture time for samples with sliver compared to those without. Fracture analysis reveals that sliver primarily contributes to performance deterioration by promoting the extension of grain boundary microcracks through grain boundary sliding during the creep process, accelerating sample fracture. Utilizing crystal plasticity theory, a successful fit was achieved for the creep rupture life of samples with sliver, allowing the prediction of fracture life for samples with different orientations of slivers. Predictive results suggest that, for CMSX-4 alloy, the orientation of the sliver should be restricted to within 8°. [ABSTRACT FROM AUTHOR]

Understanding the thermal stability of ceramic matrix composites is one of the necessary prerequisites for their engineering application. This study aimed to investigate the stress response and failure mechanism of SiC-coated C f composite during thermal shock in an O 2 free environment, at temperature between 500 and 1800 °C. Composites with a single layer of SiC coating, and a reinforcing phase are carbon fiber yarns with a three-dimensional four-step braided structure. A meso-scale finite element model considering the orientation of fiber yarns was established to analyze thermal residual stress (TRS) and thermal shock stress (TSS) by transient analysis. Results indicated that the most dangerous position generated by the TRS was in the matrix close to the fiber yarn/matrix interface. Initial cracks first nucleated in the matrix, because the matrix was subjected to large residual compressive stress along the braiding direction, which is related to the distribution characteristics of the fiber yarns (braiding method). Fiber yarns with different orientation exhibited almost the same stress state, and interaction between fiber yarns resulted in a similar "twisted" state. For single fiber yarns, the principal axis and fiber yarn/fiber yarn interface were prone to failure. TSS in the composites rapidly increased during the initial cooling stage. A sudden change in temperature and stress gradient led to cracking and peeling at the composites/coating interface. Possible failure modes and mechanisms of the composites with and without the SiC coating are discussed. [ABSTRACT FROM AUTHOR]

• Based on continuous damage mechanics, a new damage evolution law of anisotropic nickel-based single crystal materials is proposed. • Based on the crystal slip theory, creep resistance τ r e s (α) is innovatively introduced and the modified creep constitutive model of nickel-based single crystal superalloy is presented. • An anisotropic creep life prediction model for single crystal superalloy was established. The combination of macroscopic creep deformation and microscopic crystal slip is realized. • The creep parameters A, n, Q and τ r e s (α) are obtained by fitting on the basis of the slip theory of finite deformation crystals and test results. • The creep behavior of anisotropic Ni-based single crystal superalloy is simulated, the accuracy of life prediction is within 1.2 times data dispersion band. The current study is centered on the creep anisotropy of a nickel-based single crystal superalloy across a wide temperature range and with orientations of [001], [011], and [111]. Based on continuous damage mechanics, a new damage evolution law of anisotropic nickel-based single crystal materials is proposed. Based on the crystal slip theory, creep resistance is innovatively introduced and the modified creep constitutive model of nickel-based single crystal superalloy is presented. Meanwhile, in order to facilitate engineering application, an anisotropic creep life prediction model for single crystal superalloy was established based on continuous damage mechanics and crystal plasticity theory. By establishing the relationship between deformation gradient and shear strain rate on the sliding system, the combination of macroscopic creep deformation and microscopic crystal slip is realized. According to the working state of single crystal blade, a wide range of temperature creep tests at different load points were carried out. The creep parameters A (temperature dependent parameter), n (apparent stress index), Q (apparent activation energy) and τ r e s (α) (creep resistance) are obtained by fitting on the basis of the slip theory of finite deformation crystals and test results. The creep behavior of anisotropic Ni-based single crystal superalloy is simulated by using a modified life prediction model considering creep resistance in finite element framework, and the numerical results are compared with the experimental results. The results show that the constitutive formula proposed in this paper can be used to simulate the mechanical properties of Ni-based single crystal superalloys at different orientations in the wide temperature range, and the constitutive formula also can accurately predict the creep life and creep deformation with different temperatures and directions. The life prediction error is in the range of 1.2 times. [Display omitted] [ABSTRACT FROM AUTHOR]

• A creep test piece of the PDL cooling structure applied in turbine blade is designed. • The creep macro–micro fracture mechanism of the PDL cooling structure is revealed. • A creep life prediction model of the PDL cooling structure is established. This article investigates the high-temperature creep macroscopic and microscopic fracture mechanism of the porous double layer (PDL) cooling structure through experiments, and predicts the creep life of the structure using the back propagation (BP) neural network model based on the bone point stress method. The high temperature creep fracture of the PDL cooling structure is determined by the macro structure characteristics and the microstructure properties. Impingement holes and effusion holes, as stress concentration region, provide a place for crack initiation. The crack growth rate of effusion plate is greater than that of impingement plate. When the creep crack extends to a certain length, the effusion plate breaks first, and then the impingement plate breaks instantaneously. At the interface between carbide and matrix, microcracks are prone to occur due to stress concentration and inconsistent deformation, thereby promoting the initiation and propagation of macroscopic cracks. The BP neural network model based on the bone point method has a good prediction result for the creep life of the PDL cooling structure, and the maximum prediction error is 9%. [ABSTRACT FROM AUTHOR]

• In the non-isothermal creep stage, the Δε increases exponentially with the increase of the T over. After this stage, the Δε has a tendency to fall, and the material shows a new second stage of creep. • The greater the cumulative plastic deformation of the material at the end of the overheating phase, the shorter the creep life. High temperature can provide more thermal activation energy, which makes atomic diffusion easier, thus promoting rafting of γ′ phase. • The residual creep life t res gradually decreases exponentially with the increase of T over. In addition, the greater the T over , the greater the creep rate after non-isothermal. • A new creep constitutive model was proposed based on the crystal plasticity theory. Nonisothermal service conditions are one of the main abnormal failure modes of aero-engines. The creep tests of a Ni-based directionally solidified superalloy under nonisothermal creep conditions (T over = 980 °C, 1000 °C and 1020 °C) and constant load (σ = 227 MPa) were analyzed by SEM. According to the creep tests, we calculate the key creep parameters. By studying tests interrupted at different stages of creep, the microstructure evolution law is obtained. Based on the above research, an improved constitutive model is proposed. The creep behavior under different T over is simulated and calculated. The simulation results are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

To study the degradation of directionally solidified turbine blades with different service times, four parts of four cross sections are selected to examine their microstructure through scanning electron microscopy. The width of the γ-phase channel, γ' volume fraction, types of carbides, and elemental composition are chosen to characterize the damage. Creep tests are carried out at four heights on the upper and lower parts of the turbine blades, and the residual creep life is determined. The degrees of degradation of the blades are examined based on the microstructures and creep test results of the samples with respect to various service times. The results indicate that the quantitative description of the microstructure is consistent with the experimentally obtained results for the remaining creep life. The relationships between the residual lives of the small samples and the width of the γ-channel and γ'-phase volume fraction are presented in a three-dimensional graph. Based on the creep damage model, a method for predicting the remaining life of the turbine blades in service is established. The predicted results of the remaining life fit well with the model results. • The study of serviced turbine blades can obtain first-hand information. • The volume fraction and size of the γ' phase are closely related to the mechanical properties. • The degradation degree of the same part of the blades increases with the large increase of service time. • There is a good correlation between the mechanical properties and the icrostructural features of the blades. • The quantitative description of the microstructure is consistent with the test results of the remaining creep life. • Based on the creep damage model, a method for predicting the remaining lives of turbine blades in service was established. [ABSTRACT FROM AUTHOR]