In order to investigate the effect of low-angle grain boundary（LAGB） on the high-temperature creep behavior of a second-generation nickel-based single-crystal（SX） superalloy, the high-temperature creep fracture and interrupted experiments are carried out at 1100 ℃/137 MPa using plate-shaped samples with different grain boundary misorientations. The results show that after standard heat treatment, fine MC carbides are formed at the LAGB with the misorientation of 7° in alloy GB-7, while blocky M₆C carbides are formed at the LAGB with the misorientation of 12° in alloy GB-12. The high temperature creep life of the investigated alloys decreases with increasing the misorientation degree. The creep life of alloy GB-12 is only 40% of that of the single crystal alloy. Further investigation reveals that LAGB migration occurrs in both the GB-7 and GB-12 alloys during high-temperature creep, but the migration distance of the GB-12 alloy is lower than that of the GB-7 alloy. Blocky M₆C carbides in alloy GB-12 hinder the grain boundary migration, leading to strain concentrations at the LAGB region. Cracks tend to initiate at the low-angle grain boundary either inside GB-12 alloy or on its surface, leading to a significant reduction in its creep life. This study can provide guidance and data support for improving the tolerance of LAGBs in high-temperature creep.

The creep properties of a corrosion resistant single crystal superalloy at 760 ℃/800 MPa, 980 ℃/250 MPa and 1120 ℃/130 MPa are investigated. The creep fracture microstructure, fracture characteristic and dislocation morphology under different conditions are analyzed using scanning electron microscopy（SEM）and transmission electron microscopy（TEM）. The results indicate that the alloy exhibits good creep performance at 760 ℃/800 MPa, 980 ℃/250 MPa and 1120 ℃/130 MPa, with its creep curves showing similar three-stage creep characteristics. As temperature increases and stress decreases, the creep lives of the initial and acceleration stages becomes shorter, while the creep life of the steady-state stage increases. Compared to 980 ℃/250 MPa and 1120 ℃/130 MPa, the creep rate during the initial stage is faster at 760 ℃/800 MPa. Under 760 ℃/800 MPa conditions, the γ′ phase retains its cuboidal morphology. The dislocation tangles forming in the matrix channels and stacking faults forming from some dislocation cutting γ′ phase have a reinforcing effect. The creep fracture morphology of the alloy involves cleavage-like and ductile dimple mixed fracture. At 980 ℃/250 MPa and 1120 ℃/130 MPa, the alloy exhibits obvious rafting behavior and topological inversion of γ′ phase and γ phase has finished. A high-density dislocation network forming at the γ/γ′ interfaces have a reinforcing effect. No stacking faults are observed to form. Dislocations cut into the γ′ phase during the later stage of creep.The creep fracture morphology is dominated by ductile dimple fracture. At 1120 ℃/130 MPa, a small amount of lamellar σ phases precipitate along specific directions in the alloy, indicating good microstructural stability.

To meet the lightweigh requirements, the structure of castings is evolving towards thin-walled designs. Therefore, it is necessary to study the evolution characteristics of the microstructures and mechanical properties of thin-walled structures made of nickel-based superalloys. Firstly, a thin-walled casting with wall thicknesses of 1, 1.25 mm and 1.5 mm is designed. Gravity casting experiments are conducted under two different process conditions, and the microstructural analysis and mechanical property tests are carried out for two types of castings, respectively. The values of microstructural characteristics are determined, including secondary dendrite arm spacing（SDAS）, grain morphology and average grain size, as well as the size and volume percentage of the γ′ phase at different wall thicknesses of the castings under different cooling conditions. The corresponding hardness and tensile strength also are measured by experiments. The results show that SDAS increases by more than 29.9% as the wall thickness of the casting increases from 1 mm to 1.25 mm and 1.5 mm. The tensile strength of the casting fluctuates with the increase in wall thickness when the flask temperature is 900 ℃. However, the tensile strength of the casting increases as the wall thickness increases when the flask temperature is 25 ℃. The variation range of the castings cooling rates are determined through numerical simulation. The cooling rate range of castings with a sand mold temperature of 900 ℃ ranges from 16.0 ℃/s to 28.2 ℃/s while those produced with a sand mold temperature of 25 ℃ exhibit a cooling rate range of 26.2 ℃/s to 58.5 ℃/s.

The directionally solidified superalloy DZ125 is widely used as turbine blades in aero-engines. This work investigates the influence of phosphorus（P）on the microstructure, mechanical properties and crack susceptibility of DZ125 alloy. The results indicate that P primarily segregates at grain boundaries in DZ125 alloy and has little effect on γ′ phases, γ+γ′ eutectic and carbides in the alloy. When P content reaches 0.008% （mass fraction, the same below） P-rich phases form in the interdendritic regions during casting, which subsequently dissolve back into the matrix during heat treatment.When the P content is no more than 0.0039%, P shows no obvious effects on the room-temperature tensile properties or the stress rupture life at 980℃/235 MPa. However, it has a significant impact on the stress rupture life at 760℃/805 MPa: the alloy with 0.0039% P exhibits a 37% decrease in stress rupture life at 760℃/805 MPa compared to the alloy with 0.0013% P, due to the segregation of P at grain boundaries weakens the grain boundaries. When the P content reaches 0.011%, the intergranular cracks appear in the DZ125 alloy hollow turbine blades during directionally solidified process. The main reason for the increase of crack susceptibility is excessive enrichment of P at grain boundaries and precipitation of P-rich phases nearby grain boundaries, which leads to grain boundary weakening and crack initiation.

As a critical strategic material for aero-engines and industrial gas turbines, the composition/process design, optimization and process control of superalloys remain at the core of industry concerns. The present work focuses on addressing practical challenges in the development and production of superalloys and their components. It identifies key influencing factors in typical processes within the manufacturing workflow and employs a combination of advanced characterization techniques such as synchrotron radiation and high-throughput experimental methods. This integrated approach enables the design and optimization of critical process parameters for superalloy manufacturing, thereby providing foundational support for enhancing process technology, product performance, research and development efficiency, and reducing costs. Taking representative manufacturing processes involving liquid-solid and solid-solid phase transformations as examples, we explore precision tailoring strategies and validation methods for key stages including master alloy melting/remelting, synergistic particle size/morphology control in gas atomization, shrinkage porosity control during casting solidification, powder storage/desorption treatments, powder consolidation through hot isostatic pressing（HIP） and heat treatment procedures. In addition, optimal usage conditions are investigated for auxiliary materials or consumables integral to superalloy production, particularly ceramics, isothermal forging dies and brazing repair materials. Notably, the research on process tailoring reveals significant phenomena: （1）the impact of oxygen existence forms in cast and powder metallurgy alloys; （2）the influence of the initial microstructural state of alloys on the phase transformation temperature during HIP consolidation and heat treatment; （3）the formation and control of abnormal phases and defects in cast, powder metallurgy and additive manufacturing alloys, along with repair materials for brazing and ceramic refractories. The aforementioned findings establish a theoretical foundation for optimizing and tailoring superalloy process parameters and achieving precise manufacturing control, while also providing feasible technical pathways for industrial implementation.

Optimizing the directional solidification process of nickel-based superalloys is pivotal for enhancing the quality of hot-end castings in aero-engines. Traditional process optimization methods have heavily relied on empirical trial-and-error approaches, whereas numerical simulation technology is increasingly emerging as a pivotal tool. This paper presents a comprehensive review of the latest advancements in numerical simulation pertaining to the directional solidification process of nickel-based superalloys. It emphasizes modeling methodologies, simulation outcomes, and their practical applications in process optimization and defect control（such as stray grains and freckles） across various multi-physics fields, encompassing temperature fields, fluid flow and solute transport, stress-strain fields, and microstructural aspects（grains and dendrites）. A synthesis of current research reveals that numerical simulation studies still grapple with several shortcomings: a high degree of dependence on approximate boundary conditions in models; inadequate refinement and limited global optimization capabilities within process windows; incomplete numerical representations of certain crystalline defects and complex defect interactions; and substantial computational resource demands for high-fidelity microstructural simulations. To tackle these challenges, future research trends are anticipated to concentrate on deepening and integrating multi-physics and cross-scale coupling models, leveraging artificial intelligence-driven simulation and optimization, enhancing the precise characterization of solidification mechanisms in multi-component alloys, and strengthening experimental-simulation collaborative validation systems through the integration of in-situ characterization techniques with simulations. By advancing in these areas, numerical simulation technology is poised to play a pivotal role in achieving precise control over the morphology and properties of complex castings, while effectively mitigating defects.

High-temperature high-entropy alloys（HEAs）show potential to surpass traditional Ni-based alloys through multi-principal element synergy and microstructural regulation. This review systematically examines three systems: high-entropy superalloys（HESAs）, refractory HEAs（RHEAs） and refractory high-entropy superalloys（RSAs）. HESAs emulate the γ/γ′ dual-phase structure of Ni-based alloys, achieving comparable strength at 800-1000 ℃. RHEAs utilize refractory elements to form high-melting-point solid solutions with superior performance above 1200 ℃. RSAs innovate with BCC/B2 nanobasket structures, outperforming Ni-based alloys across 25-1200 ℃. Current challenges include poor room-temperature ductility, oxidation resistance and phase stability, demanding breakthroughs in multi-scale microstructure control, dynamic phase transformation mechanisms and high-throughput design. Future directions prioritize multi-objective composition optimization, advanced processing, cross-scale characterization, and service-condition evaluation systems to guide extreme-environment applications like aeroengine components and nuclear reactors, etc.

IN718 superalloy is extensively utilized in the aerospace and nuclear industries due to its outstanding oxidation resistance, heat-corrosion resistance, good structural stability, fatigue performance and safety reliability. It is one of irreplaceable materials for the hot-end components of next-generation advanced aircraft engines. Recently, laser powder bed fusion（LPBF） technology has developed as an innovative rapid prototyping technique, transcending the limitations of traditional shaping methods and structural designs. This technology has realized one-step laser near-net shaping of complex thin-walled structures, demonstrating substantial application potential. However, during the laser additive manufacturing process, the thin-walled surfaces are exposed to high laser input energy, which can readily induce warping, deformation, and even cracking, significantly impacting the service performance of these structures. To address these challenges, this work provides an overview of the working principle and recent advancements in LPBF technologies. It systematically analyses the multi-scale microstructural evolution and precipitation phase behavior of IN718 superalloy thin wall fabricated by LPBF. Special emphasis is placed on the initiation, propagation mechanisms and mitigation strategies for metallurgical defects, including optimized thin-walled structural designs, laser forming process parameters and alloy composition. In addition, the strengthening mechanisms underlying the mechanical properties of IN718 superalloy thin wall at both room and high temperatures are analyzed and discussed. Finally, the work summarizes the existing challenges such as insufficient critical performance under harsh conditions and future development directions of superalloy thin wall fabricated by LPBF, including establishment of laser forming process databases specialized for superalloy thin wall, investigation of solidification defect formation and novel control strategies in superalloy thin wall fabricated by LPBF, and optimization of the chemical composition design for high-performance superalloy thin-walled components.

Traditionally, the creep performance of superalloys are characterized under isothermal and constant-stress conditions. However, in the service environments of aero-engines, internal cooling introduces notable through-thickness temperature gradients within turbine blade materials. Consequently, examining the creep behavior of single-crystal alloys under such temperature gradients holds considerable engineering significance. This study conducts a series of temperature-gradient creep experiments based on a Ni₃Al-based superalloy. Temperature gradients of 10⁵ K/m and 5×10⁴ K/m are imposed. The results indicate that temperature gradients exert a substantial influence on specimens creep rupture life. Specifically, compared to isothermal creep, the application of a 10⁵ K/m gradient leads to an almost 46% extension in creep life, whereas a 5×10⁴ K/m gradient results in about 30% improvement. Fractographic and microstructural analyses reveal enhanced anisotropy on the fracture surface under temperature gradients. Furthermore, the oxidation behavior varies markedly across different temperature zones: the high-temperature region exhibits a denser, thinner oxide layer, whereas the low-temperature region displays a porous, thicker oxide layer. In the 10⁵ K/m gradient specimen, the low-temperature area exhibits a rafted γ′ structure, while the high-temperature area shows a de-rafted morphology, suggesting differing strain rates between these regions.

Stress rupture tests are conducted on DD10 alloy specimens with two distinct wall thicknesses at conditions of 1000 ℃/200 MPa and 1100 ℃/100 MPa. The stress damage characteristics of these specimens and the reasons for the thin-wall effect are analysisd. The findings reveal that, under both test conditions, the stress rupture life of thinner specimens is markedly shorter compared to thicker ones, indicating a pronounced thin-wall effect in DD10 alloy. Although the reduction in effective bearing area due to oxidation does expedite the creep process to some extent, the variation in effective stress increase across different wall thicknesses is minimal, within a range of just 6%. This suggests that the augmentation in effective stress stemming from oxidation is not the primary catalyst behind the thin-wall effect. Microstructural observations of the surface and longitudinal sections of the fracture reveal that, under both test conditions, the cavities and cracks in thinner specimens are smaller in size than those in thicker specimens. Furthermore, the relationship between the stress intensity factor（K） and crack length（l） indicates that, for cracks of equivalent size in specimens with varying wall thicknesses, thinner specimens exhibit a higher stress intensity factor at the crack tip, rendering the crack more prone to propagation. Consequently, thinner specimens have a shorter critical size for crack instability expansion. The disparity in this critical size among specimens with different wall thicknesses is pinpointed as a crucial factor contributing to the thin-wall effect.

Based on the hot-ended casing of K4169 superalloy as the research object, aiming at the defects such as liquid splashing, oscillation and entrained air in the linear filling process of traditional superalloy counter-gravity casting, particularly, considering the complex variable cross-section structure of the casing castings, the work explores the influence of pressurization speed on filling of such structure through hydraulic simulation experiments. The results reveal that for the variable cross-section structure, a lower pressurization speed leads to more stable liquid filling. Orthogonal experiments are conducted to ascertain the optimal filling process parameter of the casing model such as a pouring temperature of 1460 ℃, a shell temperature of 900 ℃ and an average pressurization speed of 4 kPa/s. Based on the casing model’s structure, linear and nonlinear filling pressure curves are designed, and both numerical simulations and experimental studies are performed to compare two filling methods. When comparing two filling processes with the same filling time, the nonlinear filling exhibits a 16.77% decrease in average gate speed compared to the linear filling, resulting in a more stable filling process and production of fewer overall defects in the thin wall areas of the casing. Casings filled using the linear method exhibit numerous crack defects across various regions, leading to a relatively high overall defect rate. In contrast, casings filled using the nonlinear method devoid of crack defects and contain only a few micro-pores. Non-destructive testing results also support the notion that casing castings filled by the nonlinear method have fewer defects, which validates that the nonlinear filling effectively reduces the type and quantity of defects in casing castings.

The high-temperature mechanical properties of cast nickel-based superalloy K4222 enhance through alloying of Hf. This work investigates the effect of adding mass fraction of 0.72% and 1.5%Hf on the microstructure and high-temperature stress rupture properties of the alloy. The results reveal that the addition of Hf not only increases the MC carbide content in the alloy, but also facilitates the formation of eutectic （Ni₅Hf + γ） phases. After heat treatment, M₂₃C₆ carbides are dissolved at high temperature and MC carbides are degraded, resulting in an overall reduction in the carbide content of each alloy and the elimination of eutectic phases. However, a small amount of Ni₅Hf phase remains in the 1.5%Hf alloy. Meanwhile, the results show that Hf can greatly improve the stress rupture life of the alloy. Compared with 0%Hf alloy, the stress rupture life of the 0.72%Hf and 1.5%Hf alloys increases 101.4% and 211.2% under the condition of 899 ℃/172 MPa, respectively. The improvement of Hf content will reduce the rupture plasticity of K4222 alloy to a certain extent, but 0.72%Hf still maintains good level. Further analysis shows that the addition of Hf can change the morphology of carbides, increase the grain boundary strength, reduce the occurrence of carbide cracking and intergranular cracks, and thus improve the high-temperature creep strength of the alloy.

Heat treatment is the most critical thermal process determining the properties of powder metallurgy（PM）superalloy components, with FGH96 currently being one of the most prevalent PM Ni-based superalloys. This work investigates the effects of two distinct solution heat treatment cooling methods—full air cooling quenching and combined air-oil cooling quenching—on the microstructure and properties of FGH96 alloy ring parts. The results indicate that both cooling methods yield equivalent grain sizes, ranging from grade 6.5 to 7. Notably, full air-cooled rings exhibit more homogeneous distribution of secondary γʹ phase. In contrast, rings subjected to combined air-oil cooling exhibit coarser secondary γʹ phases, with reduced quantity on the inner side compared to the outer side, attributable to internally diminished cooling rate. During the later stage of quenching, ring parts undergoing full air cooling experience a slower cooling rate than those using combined air-oil cooling. Furthermore, fine γʹ phases, possessing sizes between the secondary and tertiary γʹ phases, precipitate along the grain boundaries using full air cooling method, leading to grain boundary strengthening. This enhances tensile strength but reduces elongation and plastic elongation at 68 h in high-temperature creep tests. Additionally, due to the more uniform cooling rate throughout the ring during full air cooling quenching, the surface residual stress reduces with more uniform distribution, thereby augmenting dimensional stability during subsequent machining processes.

Based on hot compression tests of GH738 superalloy, encompassing deformation temperatures ranging from 980 ℃ to 1100 ℃ and strain rates of 0.001-0.1 s⁻¹, deformation activation energy（Q）, temperature-compensated strain factor（lnZ）, power dissipation efficiency（η） and instability factor（$ \xi (\dot{\varepsilon })$） are calculated. Subsequently, a response surface model is established, utilizing hot deformation processing parameters as input variables and targeting Q, lnZ, η and $ \xi (\dot{\varepsilon })$ as output metrics. This model facilitates the optimization of the superalloy’s heat deformation processing parameters. The results show that the superalloy’s flow stress exhibits considerable sensitivity to variations in these parameters, which significantly impact Q, lnZ, η and $ \xi (\dot{\varepsilon })$. Notably, the established response surface model demonstrates exceptional prediction accuracy, with average absolute relative errors of 0.494%, 0.564%, 0.919% and 13.484% for Q, lnZ, η and $ \xi (\dot{\varepsilon })$, respectively. Employing multi-objective optimization—aiming for low Q and lnZ coupled with high η and $ \xi (\dot{\varepsilon })$—the optimal deformation processing parameters are determined to within the range of 1092-1100 ℃ deformation temperatures and 0.001-0.0056 s⁻¹ strain rates. Microstructural analysis conducted under these optimized parameters further validates the accuracy of the multi-objective optimized results.

The machine learning technology has broad prospects in the field of aerospace materials and plays an important role in material selection, design, and optimization. Firstly, a brief discussion was made on the advantages and potential of machine learning technology in the aerospace field, outlining the technological developments, algorithm categories, features, and limitations. The conventional or potential applications of machine learning in scientific exploration, especially in complex material data formats, are introduced. Secondly, the research status of machine learning in aviation materials is mainly focused on, discussing the recent progress in utilizing machine learning to assist in the research of high-temperature alloy materials, high-strength structural materials, thermal protection coating materials, as well as functional and smart materials. The strategies and methods of machine learning-driven aviation material research are elucidated. Finally, the challenges encountered in machine learning-assisted aerospace material research and development are examined. Facilitating the transformation of aerospace material research towards the fourth paradigm of data-driven materials science necessitates efforts in promoting the open sharing of data resources, integrating domain knowledge and physical laws more deeply into machine learning models, and ensuring feature consistency across different data types.

The mechanical properties and thermodynamic stability of nickel-based single-crystal superalloys are largely dependent on the charateristics of the precipitated phase interface. In this work, density functional theory（DFT）is utilized to investigate the influence of alloying elements, specially Co, Cr, Mo, W, Re and Ta, on the mechanical properties of γ-Ni/γ′-Ni₃Al interface. Following a convergence analysis to the optimal computational model, our findings reveal that Re and W exhibit the most significant strengthening effects within both the γ and γ′ phases. Notably, Re stands out for its substantial enhancement of Young’s modulus（27 GPa and 11 GPa）and shear modulus（16 GPa and 6 GPa） in the γ and γ′ phases, respectively, while Ta demonstrates a unique proficiency in augmenting the bulk modulus of 21 GPa and 14 GPa in the γ and γ′ phases, respectively. Analysis of interfacial tensile properties indicates that the Re-doped system exhibit the highest ideal tensile strength（approximately 25 GPa）and deformation energy（approximately 1.84 J·m⁻²）. Furthermore, the strengthening impact of alloying elements on interface tensile properties diminishes in the order: Re＞W＞Cr＞Mo＞Ta＞Co＞undoped. Analyses of differential charge density and density of states reveal that the strengthening mechanisms of theses alloying elements are attributable to the augmentation in the chemical bonding strength between doped atoms and their nearest-neighbouring host atoms. Electron orbital characteristics indicate that these alloying elements contribute to retarding interfacial fracture by maintaining local structural stability. A series of results provide ideas for the development of novel nickel-based single-crystal superalloys.

Optical microscopy（OM） and scanning electron microscopy （SEM） methods are employed to investigate the effect of various load conditions—including a constant load of 200 MPa, an average stress of 200 MPa with a stress amplitude of 130 MPa, and an average stress of 150 MPa with a stress amplitude of 130 MPa—on the microstructural evolution of DZ411 alloy. The experimental findings reveal that the dendrite structure remains relatively unchanged under high temperatures and stress conditions. When compared to a constant load, DZ411 alloy subjected to cyclic loading exhibits a reduced number of interdendritic pores, which are also smaller in size. In the absence of loading, the γ′ phase undergoes rafting to form a sheet-like structure. Notably, cyclic loading exhibits a more pronounced promotion effect on the rafting growth process of the γ′ phase than directional constant loading. Additionally, cyclic loading facilitates the merging and growth of small γ′ phase particles, leading to the formation of longer sheet structures as more γ′ phases become interconnected. Furthermore, under cyclic loading, the size and morphological differences among γ′ phase particles become more pronounced.

To address the very high cycle fatigue（VHCF）issue of GH4169 nickel-based superalloy, which is widely utilized in aero-engines, a fatigue specimen subjected to 20 kHz ultrahigh frequency vibration is designed and tested utilizing a piezoelectric ultrasonic fatigue testing system. At room temperature, the P-S-N curves for VHCF of GH4169 nickel-based superalloy are obtained under various survival probabilities of 5%, 50%, and 95%. The experimental findings reveal that the GH4169 material’s curve exhibits a downward trend when the fatigue life attains 10⁷ cycles, indicating the absence of a fatigue limit and the persistence of fatigue failure. Fracture analysis results indicate that the majority of VHCF cracks initiate from the surface or subsurface of the specimen, with both single-source and multi-source cracking observed. The cracking modes encompass surface sliding cracking and non-metallic inclusion-induced sliding cracking.

The service life of single crystal turbine blades, which serve as pivotal components in aero-engines, is intricately tied to their surface integrity. To fulfill performance standards, these blades typically undergo shot peening to meet for reinforcement. This study meticulously examines the impact of surface morphology and various surface integrity indicators—including roughness, near-surface microstructure, hardness, and residual stress—on DD6 single-crystal superalloy before and after undergoing shot peening treatments of varying intensities (0.15, 0.2 mmA, and 0.25 mmA). Utilizing a surface profilometer, scanning electron microscope, microhardness tester, and stress tester, we comprehensively analyze these factors. The results show that shot peening diminishes the original machining marks on the DD6 superalloy’s surface, with surface roughness escalating from 0.507 μm at 0.15 mmA to 0.883 μm at 0.25 mmA. A gradient plastic severe deformation layer emerges near the surface, its depth progressively increasing from 45 μm at 0.15 mmA to 98 μm at 0.25 mmA. Furthermore, the surface hardness value rises steadily, from 490HV in the original specimen to 738HV at 0.25 mmA, with the hardened layer’s depth also augmenting, from 50 μm initially to 260 μm at 0.25 mmA. Notably, the alloy attains its peak residual compressive stress of approximately –821.2 MPa on the surface when subjected to a blasting intensity of 0.2 mmA.

The creep rupture properties of DD419 single crystal superalloys, fabricated at varying pouring temperatures were examined under conditions of 850 ℃/650 MPa, 1050 ℃/190 MPa and 1100 ℃/130 MPa. SEM, EDS and TEM were used to analyze the microstructure and component segregation to study their effects on the durability. The results show that as the pouring temperature decreases, the primary dendrite spacing of the alloy widens, the eutectic content and the number of micropore increase, and the γ′ phase size diminishes. Under high temperature/low stress（1100℃/130 MPa）, the γ′ phase size exerts a more pronounced influence on durability than do micropore and residual eutectic content. The finely dispersed γ′ phase enhances the alloy’s durability under all three test scenarios, with the alloy poured at 1500 ℃ exhibiting optimal durability. At intermediate temperature/high stress condition（1050℃/190 MPa）, the γ′ phase is intersected by numerous dislocations, and dispersed γ′ phase may contribute to dislocation pile-ups. Concurrently, the alloy maintains good elongation at different pouring temperatures; however, as the pouring temperature decreases, section shrinkage decreases under all three test conditions. Pouring temperature has a negligible impact on the the alloy’s fracture morphology. Specifically, the γ′ phase near the fracture surface of the specimen tested under 850 ℃/650 MPa condition remains cubic morphology, with a mixed -mode fracture mechanism. Under other durability parameters, the γ′ phase assumes a rafted configuration, leading to an all-micropore aggregation fracture mechanism.

As the turbine inlet temperatures of aero engines continue to rise, there is an urgent need to develop a new generation of single-crystal superalloys and their thermal protective coatings for turbine blades. In order to meet the stringent requirements for the comprehensive performance of high-temperature structural materials in the complex service environments of aero engines, the intelligent design research of single crystal superalloys and thermal protection coatings has been gradually carried out at home and abroad in recent years under the promotion of material integrated computational engineering and material informatics. This paper reviews the latest research progress in the design of novel single-crystal superalloys and thermal protective coatings by utilizing multi-scale computational simulations and machine learning methods. The findings confirm that multi-scale computational simulations offer robust theoretical support for understanding the strengthening and toughening mechanisms of single-crystal superalloys, as well as the oxidation resistance and diffusion protective mechanisms of thermal protective coatings. Additionally, the study highlights the reliability and significant potential of machine learning in constructing intrinsic "composition-structure-property" relationship for high-temperature structural materials. This approach paves an intelligent and efficient new pathway for the rapid development of next-generation high-temperature single-crystal superalloys and thermal protective coatings.

With the global energy transition and increasing environmental requirements, hydrogen-mixed gas turbines as a high-efficiency and low-emission energy conversion equipment has been widely concerned. This paper reviews the development status of hydrogen-mixed gas turbines domestically and internationally, analyzes the characteristics of hydrogen combustion in gas turbines, explores the impact of hydrogen combustion on complex components and the application of high-temperature materials, and analyzes the performance requirements for hot-end component materials operating under high temperature, high pressure, and corrosive conditions, as well as the main challenges and potential solutions in current material development. The effects of water vapor and hydrogen embrittlement during hydrogen combustion on gas turbine alloys and thermal barrier coatings are discussed in detail.Water vapor accelerates the oxidation and corrosion of alloys, leading to a decline in mechanical properties. Furthermore, hydrogen embrittlement significantly affects the toughness and durability of alloys, increasing the risk of crack propagation and fracture. In terms of the problems, future research should focus on multi-field coupling simulations and accelerated corrosion tests, considering the factors such as temperature, pressure, and different atmospheres to establish realistic environment simulators to evaluate alloy and coating performances. Additionally, the combined effects of hydrogen and water vapor on high-temperature alloys and thermal barrier coatings should be emphasized. This includes investigating the diffusion mechanisms of hydrogen in alloys, interactions with lattice defects, and the microscopic processes leading to hydrogen embrittlement. Building oxidation models in high-temperature water vapor environments, clarifying the dissociation and adsorption mechanisms of water vapor at high temperatures, the hydroxylation of protective oxide films Al₂O₃ and Cr₂O₃, and the growth behavior of non-protective oxides（e.g., spinel） are also essential.

The thin-wall effect of single crystal superalloys refers to the phenomenon that when the thickness of the sample and the part is less than 1 mm, the lasting life is reduced, the creep rate is increased and other mechanical properties are significantly attenuated. With the development of the internal cooling structure of advanced aero-engine single crystal blade parts, the structural thickness of some areas decreases, making it a typical thin-walled structure. Thus, it is of great engineering significance to consider the thin-wall effect in the thin-wall region during the design and manufacture of blades. Creep performance is one of the most important properties of superalloys for turbine blade application. This paper summarizes the thin-wall effect in creep performance of the superalloys as well as some advanced experimental equipment in the study of thin-wall effect. Research on thin-wall debit effect of superalloys can be divided into two categories, one is the cause of thin-wall debit, including the relative enhancement of oxidation, more significance in anisotropy, changes in microstructure and the initiation or growth of defects, and the factors that influence the thin-wall debit effect including experimental conditions（temperature, stress, etc.）, the processing methods（casting, machining）, geometric shape （rectangular cross-section, ring cross-section, film cooling holes）. Research on thin-wall debit effect is within the scope of engineering application, as a part of “component level/analog component level” in “building block” verification and evaluation technology, thin-wall debit effect research under service environment or near-service environment conditions is more valuable for application. For this purpose, a variety of advanced experimental equipment platforms have been developed to simulate one or several coupled service conditions（high temperature, high pressure, corrosion/erosion, centrifugal loading） of the blade in the engine. Future research on thin-wall effects should be carried out under conditions closer to actual service conditions by preparing specimens according to the actual blade manufacturing process and conducting experiments on the equipment that simulates the service environment.

The spot-welding defects of highly alloyed Ni-base superalloy GH4065A were investigated by using SEM and EBSD analysis methods. Effects of the welding defects on fatigue life and fracture behavior were studied by comparing thin plate samples with a central hole that were non-welded, densely welded and sparsely welded respectively. The results show that the lack-of-fusion defect, solidification crack and liquation crack are the main welding defects responsible for significant reductions in low-cycle fatigue life as well as combined low and high cycle fatigue life. These welding defects result in a transition of the fatigue crack initiation site from the inner surface of the central hole in the non-welded sample to the welding spot in the welded sample, leading to 44%-83% reductions in low-cycle fatigue life at 700 ℃/700 MPa. For the combined low and high cycle fatigue conditions（with a stress amplitude of 700 MPa for the low cycle loading part and 100 MPa for the high cycle loading part）, the welding defects not only alter the site at which fatigue cracks initiate, but also make the crack propagation mode more intergranular. This results in dramatic decreases of over 85% in the fatigue life of welded samples at both 600 ℃ and 700 ℃. Due to shorter distance between the welding spot and the central hole, densely-welded samples exhibit a slightly lower level of fatigue life under low-cycle loading conditions compared to sparsely welded samples. However, the fatigue life difference between them becomes negligible when subjected to combined low and high cycle loadings.

Advanced materials technology is the forerunner in the development of high-tech aerospace equipment and the key foundational technology supporting the modern industry. It has penetrated into all aspects of national defense construction, national economy and social life, and has become a technological highland and national defense focus that countries all around the world are competing to develop. This article focuses on analyzing the current technological status and development trend of the advanced structural materials in the aerospace field, elaborating on the aspects of high-performance polymer and their composites, high-temperature and special metal structural materials, lightweight high-strength metals and their composites, and advanced structural ceramics and their composites. The analysis results show that the current development and production of aerospace structural materials in China still face various difficulties, such as too much follow-up research and imitation, lack of independent innovation, severe technological blockade, and technical bottlenecks need to be broken. Meanwhile, the prospects for future research and development are proposed, and the significance of establishing the complete technology system of production-learning-research-application is highlighted.

With the proposal of the "dual carbon”goals, using hydrogen as zero-carbon alternative fuel has become an important trend of the aviation industry in the future. In recent years, the hydrogen-fueled aero-engines have garnered significant attention. Superalloys are the most widely used materials in the hot section components of gas turbine engines. The purpose of this review is to provide reference for the research and development of superalloys for hydrogen-fueled aero-engines future use by understanding the effects of hydrogen-related environment on superalloys currently across various fields. Internal/external hydrogen environments, hydrogen permeation（charging）methods, measurement of hydrogen concentration/distribution or stable existence temperature, the influence of hydrogen on tensile strength, the impact of hydrogen on creep/stress rupture and fatigue properties, and the fracture mechanism of hydrogen embrittlement are described. The degradation factors of mechanical properties of superalloys with different composition, manufacturing process, original microstructure, alloying degree and different application fields under hydrogen-related environment are summarized. In general, mechanical properties tests in the external hydrogen environment exhibit more significant hydrogen-assisted mechanical degradations than that in internal hydrogen environments. Superalloys with higher alloying degree exhibit more pronounced hydrogen embrittlement, while the tendency of properties decrease（creep/rupture, fatigue and tensile）in hydrogen at elevated temperature is much less than that at room temperature. The prospects for the mechanical performance evaluation of current superalloys in hydrogen-related environments for hydrogen-fueled gas turbine and the development of new alloys suitable for hydrogen environments are provided. Hydrogen-fueled gas turbine aero-engines may encounter cryogenic temperature hydrogen environment for liquid hydrogen storage, hydrogen environment for cooling, high-temperature/high-pressure hydrogen environment for gas compression, and the impact of combustion products–water vapor（humid）at elevated temperature. Diffusion or permeation of hydrogen in superalloys, the embrittlement and corrosion of alloys in high-pressure hydrogen environments, oxidation and corrosion behavior in high-temperature humid environments, as well as the degradation and protection mechanism for alloys and coatings in the aforementioned multiple coupling environments shall be concerned. It is necessary to establish hydrogen combustion environment experimental facility that closely simulates service conditions to conduct research on the impact of hydrogen-related environment on superalloys and their components. It is also essential to establish a mechanical performance database and standards for currently used key materials in hot section components such as turbine blades and disks for hydrogen related environments, and properly develop new high-temperature structural materials suitable for hydrogen combustion conditions, which will provide support for the application of hydrogen fueled gas turbine aero-engines.

Superalloys are predominantly employed to crucial aviation hot-end components such as turbine rear casings, diffusers, and pre-swirl nozzles. The investment casting technology supersedes “casting + welding” forming approaches, which reduces the number of parts and processing procedures, offers improved reliability and mass reduction. Therefore, investment casting is a pivotal technology for aviation component manufacturing. However, the casting of complex thin-walled components encounters challenges with dimensional accuracy, impacting engine aerodynamic performance and assembly precision, which has become a bottleneck problem restricting the manufacturing quality of key structural components of aero-engines in China for a long time. This article reviews the current advancement in the dimensional accuracy control for superalloy investment castings at home and abroad. A forward-looking analysis and discussion on development trends are conducted, particularly focusing on digital and intelligent technologies. There is an urgent need to build a digital twin platform for investment casting in the future and to develop more advanced accurate, quantitative and intelligent prediction methods for dimensional deformation and die profile design theory.

Additive manufacturing provides a new way to develop high-performance superalloys and components. A γ′- strengthened CoNi-base superalloy suitable for additive manufacturing was developed, and a crack-free block material was prepared by optimizing the parameters of electron beam melting（EBM） technology. The experimental results show that the lowest porosity of the alloy is about 0.14% when the scanning speed is 2000 mm/s. The microstructures of the as-printed CoNi-base alloy are columnar grains growing along the <001> direction, the average grain width is about 235 μm, and the volume fraction of γ′ phase is about 30%. After hot isostatic pressing and solution aging treatment, the porosity of the alloy is further reduced to about 0.09% with unobvious change of columnar grains. The average size of γ′ phases is about （70±18）nm with the volume fraction of about （32±3.6）%. The results of room temperature tensile tests show that the additive manufactured γʹ-strengthened CoNi-base superalloy exhibits excellent strength and ductility, showing a good potential of industrial application.

In view of the shortage of conventional design methods of pressure curve in the anti-gravity precision casting and taking the structural characteristics of the casting with variable cross-sections into account, automatic calculation of cross-sectional areas was implemented for the casting and gating system by the secondary development of CAD software, and quantitatively describing the variable feature of cross-sections of casting was realized. Based on Bernoulli and flow conservation equations, the relationship between the filling pressure and the rising speed of metal liquid level was deduced. A new design method of pressure curve based on the automatic calculation of cross-sectional areas of the casting was proposed. The simulation results of anti-gravity casting for nickel-based superalloy demonstrate that, compared with the pressure curve of the conventional design method, the new curve can reduce the peak value of filling speed from 0.611 m/s to 0.439 m/s at the minimum cross-sectional area, the falling range of which is 28.15%. It meant that the new method can effectively avoid the shock and splash of liquid metal, meanwhile, shorten the filling time, then the filling process is fast and stable. The hydraulic experiment and pouring experiment show that the new pressure curve has a smoother filling liquid level and can effectively avoid casting defects. Therefore, it proves the effectiveness of the new pressure curve design method and provides a basis for rational design of anti-gravity pressure curve.

K403 nickel-base superalloy is widely used in the manufacture of aero-engine turbine blades because of its excellent properties at room temperature and high temperature. In order to solve the problem of turbine blade crack defects caused by long-term service in complex working conditions, in this work, two different processes of （tungsten inert gas, TIG） welding and laser cladding were used to repair the blade cracks, and the microstructure and properties of the repaired region were studied. The influence of TIG welding and laser cladding repairing on microstructure, mechanical properties and failure behavior was analyzed. The results show that the microcracks tend to occur near the repair interface using the TIG welding repairing process, which are mainly caused by carbides and low melting point eutectic structure. The grain and structure of the repaired area by laser cladding repair technology are more uniform, and the microcrack defects can be easier to control. The comprehensive mechanical properties of the samples repaired by laser cladding are obviously higher than those repaired by TIG welding repairing process, and the samples repaired by laser cladding have better process stability. The tensile strengths of the samples using the laser cladding repair process and the TIG welding repair process at room temperature have reached 87.44% and 69.22% of the strength of K403 base material, respectively. According to the failure analysis results, the tensile fracture at room temperature in the repaired region presents mixed fracture characteristics, and the tensile fracture at high temperature presents intergranular fracture characteristics. Microcracks in the repaired area, local liquid phase deficiency defects and carbide structure are the main reasons of failure. The laser cladding technology has the advantages of heat source concentration and smaller heat affected zone, which can effectively restrain the defects and refine the microstructure. Therefore, the laser cladding repair process is used to repair the edge plate crack damage generated during the blade test run. After fluorescence and kerosene-chalk detection, the repairing process meets the relevant reuse requirements.

Nickel-based superalloys are important structural materials in turbine engines and gas turbines, but their conventional fabrication processes are complex, costly and have poor raw-material-utilization rate. The electron beam powder bed fusion（EBPBF） technology is a new solution for forming superalloys, which can realize near net forming of complex structural parts. During more than ten years of development, EBPBF technology has realized the high-quality formation of superalloy materials and components represented by Inconel 718 and Inconel 625, and has continuously extended its capability to form crack-free, high-γ'-phase-portion difficult-to-weld nickel-based superalloys, and can even directly prepare single-crystal nickel-based superalloy components. In this paper, the relevant literatures on EBPBF nickel-based superalloys in recent years are reviewed, and the current research status from the perspectives of printability, process optimization, property characterization of EBPBF nickel based superalloy components are analyzed and summarized, and also the future research work is proposed.

Nickel-based superalloy is an essential material to prepare hot-end components in aero-engines and gas turbines, due to its excellent mechanical properties under high temperature. Additive manufacturing（AM） is one of the most important techniques to fabricate superalloy components with complex geometry. In this paper, the research progress of microstructure and defects of AMed superalloy is reviewed. Based on the existing literature, tensile properties of GH3536, GH3625 and GH4169 are summarized. Typical applications of AMed superalloy components in aero-engines and gas turbines are presented. Finally, for the problems in existing investigations, it is suggested that the future research can focus on materials design, heat treatment/hot isostatic pressure process optimization, single crystal preparation, real-time monitoring technique development and internal surface treatment technique innovation.

Pt/Ir thin film thermocouples were prepared on the surface of the GH5188 special-shaped high temperature superalloy, and the thin film thermocouples were placed on the flame flow table to test the transient temperature of the surface of the special-shaped high temperature superalloy. After four cycles of high temperature and high-speed flame burning, the total test time reached 8700 s, the Pt/Ir thin film thermocouple can still obtain stable temperature data. The success of this test indicated that Pt/Ir thin film thermocouples have taken an important step towards engineering application. Aiming at the engineering application of thin film thermocouples, the project team investigated the thin film preparation technology, interface control, integrated preparation, signal and system, etc., broke through 13 key technologies, and realized the engineering application of Pt/Ir thin film thermocouples. The breakthrough of this experiment makes China have the ability of temperature measurement under the condition of blade simulation service.

In this paper, TWL12 + TWL20 inorganic salt aluminum coating was sprayed on the surface of Ni-based P/M superalloy. The microstructure changes of inorganic salt aluminum coating and P/M superalloy after high temperature oxidation at 700, 750 ℃ and 800 ℃ were studied by XRD, SEM, EPMA and TEM. The results show that after high temperature oxidation, the surface structure of the coating peels off, and the aluminum in the coating diffuses with the substrate to form a transition layer composed of oxidation zone, diffusion layer and interdiffusion zone. The oxidation zone is the outermost layer, where is mainly enriched with O and Al elements to form Al₂O₃ layer. The diffusion layer mainly contains Ni and Al elements, forming NiAl phase and α-Cr phase dispersed in it. Finally, the interdiffusion zone rich in Ti, Cr, Co, Ta and other elements exists between the diffusion zone and the matrix, which is mainly composed of Ni₂AlTi phase matrix and σ phase dispersed in it. The analysis shows that the thickness of transition layer changes with the increase of oxidation temperature, it is mainly manifested by the increase of the width of the interdiffusion zone, the increase of the size of α-Cr phase in the diffusion layer and σ phase in the interdiffusion zone, and the growth trend of σ phase along the vertical transition zone is intensified. The oxidation weight gain curve shows that the transition layer exhibits good oxidation resistance during high temperature oxidation at 750 ℃ and 800 ℃ after the surface structure of the coating falls off, it indicates that the TWL12 + TWL20 inorganic salt aluminum coating has the potential to provide high temperature oxidation coating protection for advanced P/M superalloy used in aeroengines.

The low cycle fatigue（LCF） properties of DD6 single crystal superalloy were investigated at 700 ℃ and R of 0.05. SEM was used to study the fracture surface and fracture microstructure. The results show that the LCF life of the alloy decreases with the increase of strain amplitude. LCF properties of the alloy are excellent under asymmetrical cyclic loading. The alloy has no transition fatigue life during LCF tests at all total strain amplitudes. LCF fatigue damage can be dominantly contributed to elastic damage and the plastic deformation is very minimal. The plastic damage increases with the increase of total strain amplitude. The crack initiation site, the fatigue crack propagation area and the final fracture zone can be observed in the fracture surface and all specimens is similar to quasi-cleavage fracture. The fatigue cracks are initiated from the micro-pores on the surface, sub-surface or far from the surface. Far from the surface crack fractures have fish-eye feature. The fatigue crack propagates perpendicularly to main stress at first and then along {111} plane. Typical fatigue striation, cleavage steps and river pattern characteristic are formed on fatigue crack propagation zone. The cleavage plane, slip band and tearing ridge are seen in the final fracture zone. Fracture microstructure analysis shows that the γ′ phase morphology far from the fracture surface still maintains cubic shape, and the slip bands are visible seen near the fracture surface, and secondary cracks are formed along slip bands.

Large size nickel-based single crystal twin turbine guide vanes（TGVs）were prepared by grain continuator（GC）technology. Directional solidification was performed in a high-rate-solidification（HRS）Bridgman vacuum furnace. Then, the macro-etching test was carried out to reveal the single crystal integrality of TGVs. Scanning electron microscopy（SEM）, electron backscatter diffraction（EBSD）technology, and high temperature stress rupture experiment were applied to evaluate the actual properties of TGVs. Simultaneously, the professional finite element modeling（FEM）ProCAST software was used to simulate the directional solidification process of single crystal TGVs. The experimental results show that the formation of stray grain（SG）defect can be avoided effectively, and integrity large size single crystal twin TGVs can be prepared successfully by adopting GC technology. However, the low angle grain boundaries（LABs）defects are formed inevitably, and the boundaries angle between primary crystal and GC crystal in Vane 1 are 1.5° and 2.7° respectively. Despite the mechanical performance at high temperature degrades slightly（stress rupture life loss less than 15%, and elongation loss less than 7%）, the service performance of TGVs is still satisfied perfectly. According to the solidification process results of the large size twin TGVs simulated by ProCAST software, it is found that the initial solidification path of TGVs is optimized, meanwhile, and the undercooling condition at the leading edge of TGVs is improved by adding the GC structure. In addition, the nucleation probability of SG defect is reduced significantly, and the formation of SG defects is avoided effectively.

The surface roughness, residual stress and micro-hardness of K4169 alloy specimens were characterized by roughness tester, X-ray diffraction（XRD）stress tester and micro-hardness tester. The results indicate that median fatigue lives of the specimens increased by 10.2-43.9 times after SP treatments compared with untreated specimens. Furthermore, the number of fatigue source decreased to only one and the site of fatigue source transferred from the surface to the subsurface. The harden layer with the depth of 0.10-0.32 mm and the surface residual stress of −941-−1023 MPa are obtained. The depth of harden layer increased with the increasing of peening intensity. The grooves obtained from the grinding disappeared and the surface stress concentration intensity decreased largely after SP. The improvement of fatigue life is mainly ascribed to the enhancement of surface integrity induced by SP.

The effect of specimen thickness on the very high cycle fatigue （VHCF） properties of DD6 nickel-based single crystal superalloys for turbine blades with hollow air-cooled structure was investigated. Based on the finite element method （FEM）, a thin-walled vibration fatigue specimen with a thickness of 0.5 mm was designed with a natural frequency of 1425 Hz, which was a suitable test efficiency for VHCF test. The VHCF test was carried out by electrodynamic shaker at room temperature, and a VHCF S-N curve up to 10⁹ cycles was obtained. Comparing with the rotational bending fatigue and vibration fatigue test data of conventional size specimens, the results show that the fatigue strength of DD6 single crystal superalloy continues to decrease after 10⁷ cycles and the fatigue strength is decreased about 25%, from 10⁷ to 10⁹ cycles; The high cycle fatigue strength of the thin-walled specimen is basically the same as the standard rotary bending fatigue strength of the same material, and slightly lower than the conventional vibration fatigue strength. The cracks in the thin-walled specimen initiate on the surface of the dangerous section, showing the characteristics of line source. There are two propagation planes in the fatigue growth zone, showing the characteristics of cleavage like.

Creep characterization of different diameter silica bar core during directional solidification of the single crystal superalloy was investigated by suspension method. The scanning electron microscope (SEM) was employed to observe the microstructure of the surface and transversal section of crept silica bar. The energy dispersive spectroscopy (EDS) and X-ray diffraction technology were used to analyse and determine the composition of the reaction product. The experimental results show that the crept deformation amount increases with prolonging of creep time and decreasing of the diameter of the silica bar. When the creep time is 60 min, the diameter 0.5 mm silica bar has the largest creep deformation, and the average deformation is 30 mm, while the 2 mm silica bar is 24 mm. The interfacial reaction of SiO₂ with C and Al, which are deposited on the silica bar surface due to the elevated temperature and low vacuum, induces the formation of porous layer. The volume fraction of the porous reaction products leads to the different crept deformation amount of different diameter silica bars. The creep deformation amount of silica bars has a linear relationship with the volume fraction of surface reaction products.

Nickel-based superalloy (GH4169) and Si₃N₄ ceramics were connected by AgCuTi composite active filler and high purity W foil which acts as interlayer. The effects of temperature on the microstructure evolution and mechanical properties of GH4169/ Si₃N₄ brazed joint were systematically studied. The results show that the effective connection of GH4169/Si₃N₄ brazed joint can be realized by using AgCuTi+W composite filler. The microstructure of the joint is GH4169/TiNi₃+TiCu+TiCu₂+Ag(s, s)+Cu(s, s)+W+TiN+Ti₅Si₃/Si₃N₄. When the brazing temperature is low, the Ti element in liquid filler diffuses to less of the ceramic interface with the filler, and no obvious reaction layer is formed; when the brazed temperature increases to 880 ℃, Ti is enriched on the ceramic side, forming a thickness of 2 μm TiN and Ti₅Si₃ reaction layer. At this time, the shear strength of the joint is the highest, reaching 190.9 MPa. With the increase in brazing temperature, the content of Ti-Cu compound, which is a brittle compound, increases and the mechanical properties of the joint are greatly reduced. The fracture results show that during the shear process, the crack initiates in the interlayer, and then diffuses into the Si₃N₄ ceramic matrix, and finally breaks on the side of Si₃N₄ ceramic.