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.

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.

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.

High temperature aging treatment was first conducted on the rejuvenated directionally solidified superalloy to simulate the re-service aging damage of turbine blades and the virgin directionally solidified superalloy respectively. Then re-service aging stability of γ′ phase in the virgin and rejuvenated directionally solidified superalloy was compared and analyzed, and the effect of different rejuvenation parameters on γ′ phase microstructure of the rejuvenated directionally solidified superalloy after the same re-service aging time was studied. The results show that although rejuvenation heat treatment can effectively restore creep microstructure to a nearly ‘‘as-new’’ condition, the re-service aging stability of γ′ phase in the rejuvenated directionally solidified superalloy is worse than that of the virgin directionally solidified superalloy, which is attributed to the decomposition of MC carbide. The rejuvenation heat treatment parameters have a great influence on re-service aging stability of the rejuvenated directionally solidified superalloy. The re-service aging rate of γ′ phase in the rejuvenated directionally solidified superalloy becomes higher, the higher the solution temperature, the shorter the holding time and the greater the cooling rate after solution higher. However, the increased primary aging temperature and holding time cause the decrease of the re-service aging rate of γ′ phase in the rejuvenated directionally solidified superalloy. The second aging condition has no obvious effect on the re-service aging stability of γ′ phase.

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.

The microstructure and mechanical properties of different heat-treated K4169 alloys after standard heat treatment (SHT), hot isostatic pressing + standard heat treatment (HIP + SHT) and hot isostatic pressing + heat treatment without homogenization (HIP + HTWH) were compared. The feasibility of heat treatment without homogenization of K4169 alloy after HIP was analyzed. A suitable heat treatment system for casting K4169 alloy was proposed. The results on microstructure show that the hot isostatic pressing (1170 °C/140 MP/4 h) can basically eliminate the Laves phase and δ phase of the alloy. Compared with the alloys after HIP + SHT, discontinuous short rod-like δ phase is existed at some grain boundaries of the sample without homogenization heat treatment (HIP + HTWH), which has no substantial influence on the uniformity of microstructure. The results on mechanical properties show that compared with the alloys after SHT, the yield strength at room temperature of alloys after HIP + SHT and HIP + HTWH is increased by 73 MPa and 91 MPa, and the stress-rupture life (704 °C / 448 MPa) is increased by 35% and 32% respectively. Although the dispersion of stress-rupture life and plasticity for alloys after HIP + HTWH are higher than that of HIP + SHT, the mechanical properties meet the requirements of AMS5383 for K4169 alloy. The HIP+HTWH heat treatment process has the practical application potential for K4169 alloy structure by comprehensive analysis of various factors such as reduction of process cost, the increase of production efficiency and the improvement of mechanical properties.

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.

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.

In this study, the third-generation rhenium containing single crystal superalloy was brazed by mixed powder filler, in which the mixed powder filler was consisted of nickel-based powder filler and the superalloy powder with the same composition of the base metal. SEM and EPMA were used to analyze the influence of the proportion of the third-generation single crystal superalloy powder in the mixed filler on the microstructure of the joint, and the high temperature stress rupture properties of the brazed joint with four kinds of solder were tested. The result indicates that the microstructures and phase compositions of the Ni-based powder filler and mixed powder filler are both consisted of γ-Ni, γ′, CrB, Ni₃B and M₃B₂ type boride, but the residue of the mixed powder filler is molten ball-type superalloy. With the thickness of brazing gap constant and increasing the ratio of the third-generation single crystal superalloy powder in the mixed filler, the precipitation of M₃B₂ type boride and low-melting point phases in the joint can be inhibited, and the distribution of borides becomes more uniform and the size becomes smaller, thus improving the uniformity of the composition and microstructure of the joint. When the proportion of alloy powder increased from 0% to 50%, the endurance life of the joint increased from 15 min to 34 hours. However, when the proportion of alloy powder increased to 60%, there are a lot of void defects in the joint, resulting in the endurance life of the joint decreased to 4 hours.

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.

Turbine blades of long-life civil aircraft and gas turbines are affected by high temperature oxidation during service, which greatly reduces the surface strength under complex working conditions and significantly shortens the service life. Therefore, oxidation resistance is one of the most specific properties that must be considered in the application of turbine blades. The influence of the different drilling processes for cooling holes on the oxidation behavior of Ni-based SX (single-crystal) superalloy at 980℃ and 1100 ℃ was investigated. The difference in the oxidation mechanism of the cooling holes under different drilling processes provided a basis for the establishment of the blade life model under service conditions. The results indicate that the film cooling holes processed by millisecond laser exhibit poor oxidation performance, and all oxidation kinetic curves basically obey the parabolic or linear law. In the initial oxidation stage of the millisecond laser specimen, the oxidation reaction is primarily determined by the growth pattern of outer NiO. Subsequently, a three-layer oxide layer（(Ni, Co)O-Spinel phase layer-α-Al₂O₃） gradually formed around the hole. There are relatively micro-holes under the internal α-Al₂O₃ layer and the γ'-free zone, which makes the oxide layer easy to exfoliate. Discontinuous α-Al₂O₃ is rapidly formed in the initial oxidation stage of the picosecond laser specimen, and then connected to each other to form the dense α-Al₂O₃ layer.

GH3536 superalloy was fabricated using Selective Laser Melting (SLM) to investigate the effect of process parameters including the laser power and scanning speed on the density, microscopic defects and surface quality of GH3536 samples. According to the measurement of density, it can be found that the density of samples increases rapidly when the laser energy density is less than 57.0 J/mm³, the density of samples fluctuates within the range of 8.30 g/cm³-8.35 g/cm³ as the laser energy density increases from 57.0 J/mm³ to 187.0 J/mm³, while the density of samples decreases slightly when the laser energy further increases. The conclusion is that the inadequate or excessive energy input reduces the density of samples. The metallographic observation shows that there are a large number of lack-of-fusion defects when the laser energy is insufficient. However, when the input laser energy is too much, many evenly distributed microcracks and gas pores appear inside of samples, indicating that defects are the main reason for low density of samples. The optimal process parameters of SLM-processed GH3536 alloy are determined by the statistical analysis of spatter particles which might cause irregular defects. Tensile properties of the sample fabricated under 175 W and 700 mm/s are tested at room temperature and the results show that the SLM-ed GH3536 superalloy has good tensile properties at room temperature.

The morphology and chemical composition evolution of mullite based refractory inclusions in FGH96 PM superalloy with powder state, hot isostatic pressing (HIP) and hot deformation (HF) were studied by means of artificial implantation of inclusions, optical microscopy (OM), scanning electron microscopy (SEM) and electrolytic etching. The mechanism of interfacial reaction between mullite based refractory inclusions and alloy matrix was revealed. The results show that in the powder state, the artificial mullite based inclusions are irregular particles, and there is no obvious change of morphology and composition in the inclusions after HIP process at high temperature and high pressure. A complex reaction layer is formed at the interface between inclusions and alloy matrix. The reaction layer is consisted of Al and Ti oxides. After thermal deformation of 1080 ℃/0.0004 s^-1 under the condition of 25% deformation rate, the main morphology and composition of the inclusions are not changed obviously. The reaction layer coated on the inclusion began to peel and elongate from the inclusion with the deformation of the superalloy matrix, and aggregated on the side close to the elongation direction with the flow deformation of the matrix. When the deformation degree is 50%, mullite inclusions and the externally coated reaction layer are broken and deformed to form an inclusion fragments and reaction layer. The inclusions in the composite form are distributed linearly, and the long axis is perpendicular to the compression direction. When the reaction layer coated outside the inclusion is stripped and the mullite inclusion is broken to form a new surface exposed to the superalloy matrix, the reaction continues to form a new reaction layer. The crushed mullite inclusion is still dominated by O, Al and Si, but it also contains a small amount of element in the superalloy such as Ni, Cr, Ti, Co and Mo.

The deformation behavior of the GH4133B Ni-base superalloy in hot working process was investigated by the isothermal compression tests carried out at the temperature of 940-1060℃ and the strain rate of 0.001-1.0 s⁻¹ with the height reduction of 50%. The microstructure of the deformed samples under different processing parameters was observed. Combined with Arrhenius hyperbolic sine equation and Zener-Hollomon parameter, the constitutive model of hot deformation of the alloy was established, and the hot working diagram was drawn. The activation energy of hot deformation of the alloy was 448 kJ/mol. the power dissipation reached its peak at 1020 ℃ and strain rate of 1 s⁻¹. Based on the establishment of constitutive model and processing map, the results of isothermal compression simulation and microstructure test analysis show that the best hot working deformation temperature of GH4133B nickel base superalloy is 1020-1060 ℃ and the strain rate is 0.01-0.1 s⁻¹.

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.

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 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.

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.

There is a problem about microstructure evolution and properties degradation for the superalloy turbine blades in long term service conditions. DZ406 alloy samples were pre-loaded to simulate the high temperature service environment of turbine blades. The thermodynamic coupling simulation conditions were 980 ℃/70 MPa, 980 ℃/110 MPa, 980 ℃/140 MPa and 980 ℃/180 MPa respectively. And then the samples were subjected to stress rupture property test at 980 ℃/275 MPa. The microstructure and 980 ℃/275 MPa rupture life of the samples under different service loading conditions were observed and analyzed. The results show that the heat treatment microstructure of DZ406 alloy is composed of carbides, residual γ +γ´ eutectic and regular γ´ phase. The morphology and size of carbides and eutectic have no obvious change with the increase of loading stress under simulated service conditions. The γ´ phase of the sample parallel to [001] direction presents different degrees of rafting, and the size of γ´ phase perpendicular to [001] direction obviously increases. The residual stress rupture life of the sample declines rapidly with the increase of service stress.

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 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.

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.

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.

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 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.

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 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.

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.

In view of the anisotropic characteristics of elastic constants of single crystal superalloys and other materials, this paper summarizes two main existing testing methods for measuring elastic moduli and Poisson’s ratio of single crystal superalloys: static method and dynamic method, and analyses the research status of elastic moduli and Poisson’s ratio of single crystal superalloys both at home and aboard. Also, the main problems and feasible solutions in current research both at home and abroad are summarized. And it is pointed out that there is no special testing standard for the elastic moduli and Poisson's ratio of single crystal superalloys. Compared with foreign countries, there is still an obvious gap in the testing and characterization technology in China, and effect of crystal orientation on elastic moduli and Poisson's ratio is often neglected in engineering applications. So it is necessary to estimate the influence of errors in measuring elastic constants of single crystal alloys by exiting testing standards. Meanwhile, this paper describes how to establish the quantitative relationship between crystal elastic moduli and arbitrary crystal orientation for single crystal superalloy DD6 through linear regression analysis of crystal orientation index and elastic moduli.

Surface integrity state after machining has an important effect on the service life of metal parts and components. The effects of four kinds of surface integration processing methods on the high-temperature fatigue properties of FGH95 alloy were investigated. These four surface processing methods were AR (grinding), GCSSP (grinding and cast steel shot peening), GCSP (grinding and ceramic shot peening) and GDSP (grinding and double shot peening). The surface roughness, residual stress distribution and micro-hardness were characterized by roughness tester, X-ray diffraction (XRD) stress tester and micro-hardness tester. The rotating-bending fatigue life with notched specimens (stress concentration factor, K_t = 1.7) was investigated. The results indicate that the fatigue life of specimens increased largely by GCSSP, GCSP and GDSP compared with AR specimens respectively. Furthermore, GDSP process can obtain the best surface residual stress field distribution, gradient distribution of micro-hardness, surface roughness and improvement of the high-temperature fatigue property.

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.

High-temperature structural materials are the key materials of aeroengine. Nickel-based superalloys are widely used in the blades, turbine discs, combustion chambers and other hot parts of advanced jet engines. However, the impurities are inevitably introduced into nickel-based superalloys during the process of physical metallurgy, vacuum casting and so on. With the continuous improvement of the performance requirement of superalloy parts, the impacts of impurities on the properties of superalloys have been paid more and more attention. As one kind of terrible impurities, sulfur still has a tremendous negative impacts on the properties of materials although its concentration is extremely low. Through integrating the experimental and the first-principles studies, this work comprehensively reveals the effect of sulfur on the structural evolution of nickel-based superalloys and its segregation behavior at the interface of superalloy substrate, oxides layer and coating. Moreover, the contributions of sulfur to the mechanical properties, oxidation resistance, hot corrosion properties and the coating performance are summarized and discussed thoroughly.

The effect of temperature on surface oxidation characteristics of nickel-base superalloy GH4169 powder was investigated by field emission scanning electron microscope (FE-SEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The results show that the surface of the GH4169 superalloy powder is partially oxidized at room temperature（RT）, and on the surface there are elemental states dominated by Ni, Cr, Ti and Nb, and hydroxide/oxide dominated by Ni(OH)₂, Cr₂O₃, TiO₂ and Nb₂O₅. With the temperature increasing (150～250 °C) , the peaks of Ni, Cr, Ti and Nb elements become weaker, the degree of oxidation is slightly increased and the surface of powder is partially oxidized. When the temperature reaches to 350 °C, the peaks of Ni, Cr, Ti, and Nb elements are all disappeared, and the surface of powder is fully oxidized. The oxide layer thickness is about 5 nm, and is mainly composed of Ni(OH)₂, Cr₂O₃, TiO₂and Nb₂O₅. The effect of temperature on oxidation characteristics of the GH4169 superalloy powder is significant, and the maximum treatment temperature of the GH4169 superalloy powder used for this study is no more than 250 °C exposed within 1 h under atmospheric conditions.

The research and development in liquid metal atomisation and forming technologies of high performance metallic materials with the emphases on gas atomised superalloy powders, spray formed superalloys, powder metallurgy TiAl alloys and spray formed high-speed steels at Beijing Institute of Aeronautical Materials are reviewed. The technology and equipment of argon atomisation and minus atmospheric pressure atomisation (i.e. atomisation in sub-atmospheric pressure atomising assembly) of superalloy powders were established. Major factors contributing to powder oxygen content, particle size and non-metallic inclusions have been identified. A variety of high-purity, fine-grained and high-quality spherical powders of superalloys were produced , which have been utilised in the research and production of hot section components, such as turbine disks in advanced aero-engines. Spray forming technologies of highly-alloyed materials were investigated and developed while taking the key technical issues for making sound performs into process consideration, such as formation and deposition of droplets, densification and shape control, and hot working of preforms. The relative densities of as-deposited performs of superalloys and high-speed steels could be higher than 99.0% after the optimisation of process parameters. Low cost and high performance spray formed superalloys and high-speed steels were developed. Spherical powders of TiAl alloys with high purity and low oxygen content were obtained using the argon atomization techniques, and high performance sheets were subsequently deformed.

The titanium alloy-superalloy dissimilar material composite structure can give full play to the respective advantages of the two materials and achieve complementary performance, which has important application prospects in the field of aeroengine manufacturing. In this paper, the (V-15Cr)+0Cr13 intermediate layer structure was designed for TC4-GH4169 composite structure, and was prepared by laser melting deposition technology. The effects of the laser power and the powder stacking method on the metallurgical quality of the interface of the laser melting deposited TC4-GH4169 dissimilar material were studied. The results show that the interface metallurgical control of the (V-15Cr)+0Cr13 composite interlayer is a key factor affecting the metallurgical quality of TC4-GH4169. For the powder feeding laser melting deposition process, when the laser power is 400 W, there is no effective metallurgical reaction between 0Cr13 and V-15Cr due to the low laser energy, resulting in interlayer peeling; when the laser power is 600 W, a small amount of brittle σ phase appears at the interface of (V-15Cr)/0Cr13; when the laser power is increased to 800 W, there is a greater dilution ratio between the 0Cr13 and V-15Cr cladding layers, and the continuously distributed σ phase with a thickness of about 20 μm is formed at the interface. By using powder presetting laser melting deposition process and focusing the laser on the surface of the V-15Cr layer, the dilution ratio between the 0Cr13 and V-15Cr cladding layers can be controlled at a reasonable level, the formation of the σ phase at the interface can be effectively avoided. The shear test results show that the fracture occurs in the V-15Cr alloy layer. The interfacial strength reaches 299 MPa and the strength coefficient reaches 0.61.

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.

Co-based superalloys casting ingots were prepared by vacuum smelting furnaces, and the influence of Ni content on the microstructure and lattice misfit of Co-based superalloys were studied by X-ray diffraction analysis (XRD) and scanning electron microscope (SEM). The effect of Ni content on the properties of Co-based superalloys was studied by high temperature compression test. The results show that the average size of the γ′ phase increases with the increment of Ni content. When the Ni content rises from 0% to 15%, the volume fraction of the γ′ phase in the alloy increases gradually, which peaks at 15% Ni content.After that the volume fraction of the γ′ phase decreases slightly when the Ni content increases to 20%.When the Ni content increases from0 to 10%, the lattice misfit between γ/γ′ phase decreases.While the misfit of the γ/γ′ phase increases slightly when the Ni content raises to 20%.The Ni content increases from 10% to 15%, the lattice misfit of the γ/γ′ phase begins to decreases again. Through the test of high temperature compression of the alloy, the yield strength of the alloy with 5% Ni content is the highest.

The evolution rule of γ′ phase in typical cross sections of DD6 single crystal superalloy turbine blade was investigated experimentally by SEM. The results show that comparing with the as-cast microstructures, the γ′ phase sizes of typical cross sections in the interdendrite regions of the heat-treated turbine blade are obviously refined, the γ′ phase sizes of the interdendritic (ID) region and dendritic core (DC) tended to be the same, and the γ′ phase size dispersion tended to decrease, the γ′ phases cubed degree increased. The sizes of as-cast and heat-treated γ′ phase in the dendrite core and interdendritic region of each cross section of the blade follow the normal distribution law. The size of γ′ phase in the section of the heat-treated blade is smaller than that of the tenon, and the size of the γ′ phase in the middle of the section is larger than that of the leading edge and trailing edge.