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The occurrence of recrystallization will greatly decrease the service life of superalloy blades. The dynamic recrystallization of a Ni-based single crystal superalloy under supergravity stress and high temperature was studied. When tested at 950 °C, only one recrystallization layer is formed on the surface, whereas this changes to two recrystallization layers when tested at 1050 °C. The supergravity produces a stress gradient in the sample, and the nucleation and growth of the recrystallized grains increase with the stress at both temperatures. This work helps to recognize the recrystallization behavior of superalloy under service conditions.

The difficulty in grain refinement during the casting of superalloy turbine guides is the primary factor of their low percent of pass. This study innovatively employs the electromagnetic oscillation (EMO) process during pouring and solidification using self-developed device to break through this problem. The effect of various process parameters on blade microstructure is also investigated. The result shows that implementing 300 A/20 Hz optimal EMO process produces uniformly fine equiaxed grains, reducing average grain sizes by 71.83% at the blade concave and 75.80% at the inlet edge. Yield and tensile strength increased by 22.34% and 27.15%, respectively, reaching a tensile strength of 1208.09 MPa. Elongation and section shrinkage also increased by 69.67% and 19.57%, respectively. The forced oscillation of melt caused by alternating magnetic field flushes and fragments dendrites, creating numerous nucleation sites, thus promoting grain refinement. The current intensity is linearly correlated with the electromagnetic force within the melt, influencing consequent oscillation effects. The optimal electromagnetic oscillation penetration depth, calculated at 42 mm, is determined by the number of oscillations and skin effect. This depth, calculated based on the inherent properties of the alloy, is instrumental in ascertaining the optimum current frequency for this model of turbine guides, applicable across different alloy compositions. The tensile deformation behavior of castings is altered by the grain refinement induced by the EMO process, enhancing tensile properties through the promotion of more homogeneous deformation and the inhibition effect of grain boundaries and one-dimensional defects on dislocations.

The sensitivity of grain boundary (GB) cracks often limits the high-temperature plasticity of superalloys. The 750 ℃ tensile deformation of fine-grained Ni-Co based wrought superalloys was observed in situ using a scanning electron microscope (SEM) equipped with an electron backscatter diffraction (EBSD) probe to clarify the texture formation and GB response. The GB stress concentration depends on the grain orientation and slip system alignment on both sides. This reflects the ability of GBs to cope with deformation incompatibility. This study provides valuable insights for predicting the failure of polycrystalline superalloys and offers new ideas for microstructure evaluation and GB design.

Abstract The enhanced performance of aerospace equipment drives parts development towards integration, complexity, and structural optimization. This advancement promotes metal near-net fabrication technologies like wire electrical discharge machining (WEDM) and 3D printing. However, the high initial surface roughness from WEDM or 3D printing poses significant challenges for the high-performance surface finishing required. To effectively reduce the surface roughness of the workpieces with high initial surface roughness, this paper proposes pulsed unipolar-polarisation plasma electrolytic polishing (PUP-PEP). The study examined the material removal mechanisms and surface polishing quality of PUP-PEP. This technique combines the high current density and material removal rate of the electrolytic polishing mode with the superior surface polishing quality of PEP through voltage waveform modulation. For an Inconel-718 superalloy part fabricated by WEDM, PUP-PEP reduced surface roughness from R a 7.39 μm to R a 0.27 μm in 6 min under optimal conditions. The roughness decreased from R a 7.39 μm to R a 0.78 μm in the first 3 min under pulsed unipolar-polarisation voltage, resulting in a remarkable 233% increase in efficiency compared to that with conventional PEP. Subsequently, the voltage output voltage is transformed into a constant voltage mode, and PEP is continued based on PUP-PEP to finally reduce the workpiece surface roughness value to R a 0.27 μm. The proposed PUP-PEP technology marks the implementation of ‘polishing’ instead of conventional rough-finish machining processes, presenting a new approach to the surface post-processing of metal near-net fabrication technologies.

This work investigates the effect of cyclic creep on the long-term oxidation of a directionally-solidified nickel-based superalloy DZ445 up to 1800 h. The stress application of cyclic creep refines the oxides, increases the oxidation weight gain, reduces the oxidation rate exponent, and decreases the activation energy. It enhances the content of Al2O3 and TiO2 in the outermost layer and in the sub-outer layer of CrTaO4 in the film. It delays the formation of the continuous innermost layer of Al2O3 and the sub-inner layer that is rich in Al2O3. The change of phase content and type in the oxidation layers could be ascribed to the diffusion kinetic effect of cyclic creep stress in the superalloy.

A deformed superalloy with γ′ content reaching 73% has been designed by ourselves. In this work, the problems of preparation and deformation caused by the high γ′ phase content were solved by the electron beam smelting layered solidification technique (EBS-LST) and hot extrusion. Initially, the superalloy with low segregation and fine microstructure was prepared by EBS-LST, followed by conducting hot deformation experiments at different temperatures and strain rates. The compression curves are corrected, and the constitutive model, recrystallization models and thermo-mechanical processing maps were established based on the corrected curves, and the recrystallization mechanisms were analyzed by TEM and EBSD. Finally, the suitable hot extrusion parameters were obtained indirectly through the hot processing map, and the designed alloy was hot extruded. The microstructure of the extruded alloy is free of cracks and is characterized by fine equiaxed grains.

The interfacial behaviors between protective coatings and substrate single-crystal superalloys significantly impact their service performances. This work focuses on the elements interdiffusion and microstructural evolution at the interface between a NiCrAlY coating and a series of high-Mo Ni3Al-based single-crystal superalloys, through the coupled phase-field simulations and DICTRA kinetics calculations of their model systems. The critical roles of Al and Cr played in the microstructural evolution at coating/superalloy interface have been confirmed, which requires the appropriate content decreases of Al and Cr in the coating at 1100 °C. However, the addition of Mo reduces the driving force of element diffusion from coating to substrate by increasing the activities of Al and Cr in superalloy. Moreover, increasing the Mo content in superalloy from 8 wt% to 10 wt% could also counteract the promoting effect of Al on Ni mobility and mitigate the γ′ coarsening and detrimental TCP precipitation. Therefore, the effects of Mo enable the reasonable increase of Al content in coating to better balance the interfacial stability and oxidation resistance of coated superalloy, besides its advantage in reducing the anisotropy of TCP precipitate. The obtained interfacial evolution mechanisms resulting from the phase transformation thermodynamics and element interdiffusion kinetics are expected to aid the coating design for advanced single-crystal superalloys servicing at ultra-high temperature.

Purpose – As an advanced manufacturing method, additive manufacturing (AM) technology provides new possibilities for efficient production and design of parts. However, with the continuous expansion of the application of AM materials, subtractive processing has become one of the necessary steps to improve the accuracy and performance of parts. In this paper, the processing process of AM materials is discussed in depth, and the surface integrity problem caused by it is discussed. Design/methodology/approach – Firstly, we listed and analyzed the characterization parameters of metal surface integrity and its influence on the performance of parts and then introduced the application of integrated processing of metal adding and subtracting materials and the influence of different processing forms on the surface integrity of parts. The surface of the trial-cut material is detected and analyzed, and the surface of the integrated processing of adding and subtracting materials is compared with that of the pure processing of reducing materials, so that the corresponding conclusions are obtained. Findings – In this process, we also found some surface integrity problems, such as knife marks, residual stress and thermal effects. These problems may have a potential negative impact on the performance of the final parts. In processing, we can try to use other integrated processing technologies of adding and subtracting materials, try to combine various integrated processing technologies of adding and subtracting materials, or consider exploring more efficient AM technology to improve processing efficiency. We can also consider adopting production process optimization measures to reduce the processing cost of adding and subtracting materials. Originality/value – With the gradual improvement of the requirements for the surface quality of parts in the production process and the in-depth implementation of sustainable manufacturing, the demand for integrated processing of metal addition and subtraction materials is likely to continue to grow in the future. By deeply understanding and studying the problems of material reduction and surface integrity of AM materials, we can better meet the challenges in the manufacturing process and improve the quality and performance of parts. This research is very important for promoting the development of manufacturing technology and achieving success in practical application.

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.

This work elucidates the interactions between Re and hydrogen at γ/γ′ interfaces, enhancing the hydrogen-embrittlement resistance of nickel-based single-crystal superalloy (Ni-SX). The H-charged Ni-SX exhibits severe embrittlement characterized by the appearance of parallel dislocation slip bands and micro-cracks, which could be effectively mitigated through improving the Re content. The segregation behaviors of hydrogen at γ/γ′ interfaces, as captured by hydrogen microprint technique, significantly diminish interfacial cohesion strength by reducing the local atomic bonding strength. Detailed characterizations of bonding charge density highlight that Re plays a crucial role in reducing hydrogen embrittlement susceptibility by suppressing the hydrogen-induced degradation of bonding strength.

The microstructure evolution under over-temperature （1070-1250 ℃） and tensile/compressive stress （30-90 MPa） conditions of IC10 alloy was analyzed to simulate the alloy deterioration process during over-temperature operation of gas turbine blades.The results show that the degeneration of secondary γ' phase in IC10 alloy during thermal exposure without stress includes spheroidizing， coarsening， and redissolution. As thermal exposure temperature and time increase， the shape of secondary γ' phase transforms from flower-like to rounded cubic and spherical， driven by the decrease of γ/γ' phase interface energy. The area fraction of secondary γ' phase decreases with the increase in temperature and the prolonging of time. The secondary γ' phase is completely redissolved after thermal exposure at 1225-1250 ℃ for more than 50 h. The size of secondary γ' phase increases with the increase in temperature and time. The coarsening of γ' phase conforms to the Lifshitz-Slozov-Wagner theory controlled by diffusion. Under the overtemperature and stress condition， the rafting of γ' phase gradually intensifies with the increase of temperature. The tensile stress promotes the N-type rafting of γ' phase perpendicular to the stress axis， while the compressive stress promotes the P-type rafting of γ' phase parallel to the stress axis. The γ' phase rafting process is faster under the tensile stress state than under the compressive stress. The microstructure of IC10 alloy under over-temperature and stress conditions can be used to evaluate the service conditions of the blade after service.

A method of quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) based on oxygen reaction mode was established for the accurate determination of trace impurity elements in superalloys. The effect of the collision/reaction mode on the removal of mass spectral interference was investigated. By contrast, the polyatomic mass spectral interference on the target element Cd can be effectively removed under oxygen dynamic reaction cell (DRC-O2) mode. The signal-to-noise ratio (SNR) peaked when the gas flow was 2 mL/min, and the detection limit was approximately three orders of magnitude lower than that under standard (STD) mode. In addition, the elimination mechanism of mass spectrometric interference was studied. It was found that for the element X (X=Rb, Nb, Mo, Cs, Ta, W or U), the conversion of the interferent species XO to the non-interferent species XOO is a spontaneous reaction when the bond energy of X−O bond is higher than that of O−O bond. Therefore, it is easier to generate ions of XOO species when there is adequate O2 present in the ion source, so as to eliminate XO interference. Based on these results, experiments were carried out to determine elements of Rb, Nb, Mo, Cs, Ta, W and U. The matrix simulated solutions containing high concentration of Mo, Nb, Ta, and W were used to evaluate the methodological parameters for the measurement of trace Cd, Ag, Au, and Hg impurities, respectively. The limit of detection (LOD) of the trance elements is 0.08-0.31 μg/g, the relative standard deviation (RSD) of the measurement is 2.3%-3.1% (n=6), and the spiked recovery is in the range of 98%-103%. The reliability of the method was further verified by certified superalloy reference materials. Finally, the trace impurities in three types of superalloy samples were measured. The results indicated that the proposed method can achieve rapid, reliable analysis with low detection limit. Besides, it can meet the measurement requirement of trace impurities when the main elements of Mo, Nb, Ta and W exist in superalloy.

The goal of this study is to investigate the impact of beam deflection pattern characteristics on microstructure and porosity formation during Powder Bed Fusion Electron Beam Melting (PBF-EB/M) processing of Inconel 718. Specifically, the complex interplay between “beam return time” and “beam jump distance” and their influence on heat accumulation, porosity, and grain formation is explored. The findings reveal that beam jump distance plays a critical role in the transition from columnar to equiaxed solidification, while beam return time is essential for achieving optimal heat accumulation and minimizing porosity. By controlling these two universal beam deflection pattern characteristics, a novel multi-spot scanning strategy was developed, enabling the formation of a fine-grained equiaxed microstructure. It is demonstrated that sufficient heat accumulation is essential for a pore-free bulk material and can be achieved by short beam return times or small beam jump distances. However, for equiaxed grain formation, a large beam jump distance, i.e., a wide distribution of melt pools, is required. Therefore, heat accumulation must be controlled by means of the beam return time if equiaxed grains are aimed for. Additionally, it is found that higher beam currents are beneficial for equiaxed grain formation, but the strongest impact on the columnar to equiaxed transition is attributed to the beam movement pattern itself. This approach offers insights into microstructure control and process reliability, regardless of the specific PBF technique employed, and enables application-specific microstructure design of Inconel 718.

Owing to their unique high-temperature mechanical properties and outstanding high-temperature oxidation resistance, superalloys have become key materials in aviation, aerospace, petrochemical, metallurgy, electric power, automotive, and other industrial fields. Due to the structural complexity and high manufacturing cost of the hot sections of aeroengines, vessel engines, and gas turbines, the development and practicality of superalloy welding technology are critical to satisfying the design and maintenance requirements of hot sections. In this work, the research progress of superalloy fusion welding is described. Its advantages and application scope, such as arc welding, electron beam welding, and laser welding, are elaborated. Common types of welding cracks are introduced, and the mechanisms and influencing factors of solidification cracks, liquation cracks, strain-age cracks, and ductility-dip cracks are summarized. The primary techniques to enhance the weldability of fusion welding are also examined in terms of heat input, material composition, microstructure, and welding residual stress. The requirements for the temperature-bearing level of superalloys in industrial development are constantly increasing; thus, the types of superalloys are also being iteratively updated. They have evolved from deformed superalloys to ordinary cast polycrystalline superalloys to novel superalloy materials such as directional solidification and single-crystal superalloys. Thus, continuously conducting welding research on emerging superalloys, traditional nonweldable superalloys, and dissimilar materials that are extremely incompatible with metallurgy is necessary. Because the composition and microstructure of the base material have an important bearing on weldability, it is necessary to strengthen the composition design of emerging superalloys and conventional nonweldable superalloys in future works. Moreover, it is critical to pay attention to the improvement of welding process technology and pre- and post-weld treatment methods. In particular, research on detection and elimination measures of welding residual stress should be strengthened, which is one of the most effective approaches for lowering the weld crack-sensitivity of superalloys. This is of great importance for synergistically enhancing the welding performance of superalloys. Moreover, monitoring and simulation techniques for the welding process can be used to perform in-depth research on scientific issues such as molten pool flow and welding heat and mass transfer during the fusion welding process. This is of great scientific value for promoting the development of fusion welding technology. Based on the foundation of enhancing welding processes, future work on automation and intelligence of welding processes should also gradually deepen, which is one of the important directions to improve welding stability and reliability and promote the widespread application of superalloy fusion welding.

The study investigates the effects of oxygen-sulfur content, holding temperature, and time on the wettability and interfacial reactions between DD5 superalloy and Al2O3-based ceramic shells through non-in-situ sessile drop experiments. Lowering the oxygen-sulfur content in the DD5 master alloy, as well as reducing the holding temperature and time, leads to an increase in the wetting angle and a mitigation of interfacial reactions. Improved wettability promotes interfacial reactions, while intensified interfacial reactions further spread the alloy melt, enhancing its wettability. The main products of the interfacial reaction between the DD5 alloy and Al2O3-based ceramic shells are Al2O3 and Si, with the process being influenced by the presence of Al. When the oxygen-sulfur content is controlled within 6 ppmw, the wettability will undergo a characteristic transformation, resulting in a sharp increase in the wetting angle. It demonstrates that the ultra-pure DD5 master alloy plays a crucial role in reducing wettability and interfacial reaction, as well as slowing down the tendency of the hetero-crystal formation. Therefore, it is of great engineering significance to further reduce the content of oxygen-sulfur impurity elements in DD5 superalloy.

Abstract Additive Manufacturing (AM) is revolutionizing aerospace, transportation, and biomedical sectors with its potential to create complex geometries. However, the metallic materials currently used in AM are not intended for high‐energy beam processes, suggesting performance improvement. The development of materials for AM still faces challenge because of the inefficient trial‐and‐error conventional methods. This review examines the challenges and current state of materials including aluminum alloys, titanium alloys, superalloys, and high‐entropy alloys (HEA) in AM, and summarizes the high‐throughput methods in alloy development for AM. In addition, the advantages of high‐throughput preparation technology in improving the properties and optimizing the microstructure mechanism of major additive manufacturing alloys are described. This article concludes by emphasizing the importance of high‐throughput techniques in pushing the boundaries of AM materials development, pointing toward a future of more effective and innovative material solutions.

Superalloys play a critical role in aerospace applications due to their exceptional mechanical properties at high temperatures. The application of magnetic fields to regulate superalloys presents novel avenues for optimizing microstructures, controlling solidification defects, and enhancing their high-temperature properties. This paper provides a comprehensive review of research findings on the influence of magnetic fields on the microstructure and properties of superalloys. It systematically elucidates the effects of different types and intensities of magnetic fields on alloy solidification. Moreover, this paper extensively explores the effects of various types of magnetic fields on the phase composition, microstructure, and properties of superalloys, including Ni-based and Co-based alloys, as well as high-entropy alloys. The underlying mechanisms behind the impact of magnetic fields on these alloy types are thoroughly analyzed. Finally, the last section offers a brief summary of the current development status and prospects of magnetic field-regulated superalloys.

This paper investigates the distribution pattern of welding porosity defects in annular weld seams of superalloy during laser welding. The results reveal that the initial portion of the annular weld seam exhibits a higher density and larger size of porosity defects compared to the ending portion. At a laser power of P = 360 W, the numerical simulation combination showed that the A1 region's average cooling rate is 8.767 × 103 °C/s and the A2 region is 8.151 × 103 °C/s that the thermal conduction effect at the initial welding position leads to an elevation in the base metal temperature in the subsequent unwelded region, thereby reducing the solidification rate of the molten pool in the latter half of the weld seam and effectively decreasing the porosity rate at the weld seam. Furthermore, the study demonstrates that elevating the base metal temperature can effectively modify the cooling rate of the molten pool, thereby influencing the formation of porosity defects. At a laser power of P = 360 W, increasing the base metal temperature to 600 °C reduces the cooling rate of the molten pool from 8.767 × 103 °C/s at a base metal temperature of T = 20 °C to 7.451 × 103 °C/s, leading to a decrease in the porosity rate from 3.357% to 0.022%. At a laser power of P = 672 W, increasing the base metal temperature to 600 °C reduces the cooling rate of the molten pool from 6.781 × 103 °C/s at a base metal temperature of T = 20 °C to 5.056 × 103 °C/s, leading to a decrease in the porosity rate from 8.214% to 0.002%. The increase in laser power brings more heat input, so the solidification rate of the molten pool decreases, but the porosity increases significantly. However, increasing the base temperature can effectively suppress the porosity defects under different laser powers. The research further reveals the relationship between welding porosity rate and cooling conditions, providing a control strategy for achieving low porosity rate welds.

Nickel-based single-crystal superalloys are designed for extreme conditions due to their superior corrosion and creep resistance properties. However, these pose challenges in the subsequent recycling after reaching their end-of-life. Molten magnesium (Mg) can rapidly corrode the stable spent nickel-based superalloys and selectively dissolve nickel (Ni). This waste-free process represents an effective method for recycling spent superalloys and accomplishing metal regeneration. This study investigates the mechanism of selectively dissolving Ni from DD5, a nickel-based single-crystal superalloy, by optimizing process temperature, time, and Mg content in an inert atmosphere. Vacuum distillation was employed to separate the resulting Mg, residual superalloy (i.e., the material left post-extraction), and Ni-rich alloy (i.e., the metal product selectively extracted). The findings revealed that the residual superalloy after selective Ni dissolution is characterized by a porous skeleton structure with pore sizes predominantly ranging from 2 to 30 nm and a low compressive strength which is 1/10 of the original DD5 superalloy.

Carbon nanofibers (CNFs) and graphene nanosheets (GNs) are introduced to obtain nano-sized TiC particles in a novel additive manufactured Ni-Co-based superalloy. The double strengthening effects of reaction-induced TiC and remaining CNFs/GNs are conceptualized in the present paper. The CNFs and GNs act as heterogeneous nucleation sites for the formation of uniformly distributed TiC nanoparticles, which inhibits the crack and homogenize the microstructure. Interestingly, the existence of remaining GNs/CNFs is revealed via 3D atom-by-atom tomographic reconstruction technology for the first time. This unique combination of nanoparticles and residual CNFs/GNs nanofillers has great potential to develop superalloys with excellent properties.

As major forming elements of γ′ strengthening phase, Al and Ti are critical for achieving superior properties of Ni-based superalloy. However, Al + Ti over 6 wt% leads to poor printability and cracking during additive manufacturing. In this work, the printability and properties of a nickel-based superalloy with Al + Ti reaching 7 wt% is synchronously improved via alloying minor Sc, the mechanism behind that is revealed by investigating the effects of Sc on the grain size, precipitation, and tensile fracture behavior of that nickel-based superalloy. This work provides a promising alternative method for optimizing the performance of superalloys prepared by additive manufacturing.

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.

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.

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 additive manufacturing of high-γ′ precipitation-rate superalloys presents both benefits and challenges. For the fabrication of dense and crack-free K417G superalloy, this study utilized laser metal deposition (LMD) in conjunction with induction heating, conducting a comprehensive experimental exploration. The findings demonstrate that a medium energy density promotes densification. The microstructure of deposited K417G includes γ matrix, γ′ precipitation, MC carbides, and γ/γ′ eutectic. The cracking mechanism during the LMD process is intricately related to process parameters. Insufficient energy density leads to the formation of unmelted powder, resulting in localized oxidation and subsequent oxide-induced cracking. In other scenarios, it manifests as liquation cracking. Moreover, an increase in preheating temperature to between 700 °C and 900 °C induces additional ductility-dip cracking. However, by raising the preheating temperature to 1100 °C and maintaining a moderate energy density, crack-free deposits can be achieved. Such conditions not only mitigate thermal stress, but also minimize phase transition stress by preventing repeated γ′ dissolution and precipitation, resulting in a more homogeneous γ′ dimensions distribution. This study confirms the printability of K417G superalloy and enhances the technological understanding of using LMD in conjunction with induction heating to prepare non-weldable superalloys.

To cater to the diverse requirements of industrial applications, it is crucial to conduct a comprehensive investigation into the influence of laser shock peening (LSP) with and without coating (LSPwC) on the microstructure and mechanical properties of materials. This study employs various methods to compare and analyze the effects of LSP and LSPwC on the microstructure and mechanical properties of GH4169 alloy. One notable contrast between LSP and LSPwC lies in the formation of oxide layers and microcracks on the surface of LSPwC-treated samples. Tensile tests subsequently reveal that LSP enhances the tensile strength, whereas LSPwC diminishes it. The reduced strength in LSPwC-treated samples can mostly be attributed to the oxide layer and microcracks resulting from laser-induced heat, as determined through failure analysis. After the removal of the oxide layer, the strength undergoes a significant improvement with LSPwC treatment, surpassing both the strength and ductility levels observed in GH4169 treated with LSP alone. These improvements can be attributed to a combined effect involving the removal of the oxide layer and microcracks, the formation of a gradient hardened layer, and the presence of dense slip bands.

In this work the effect of crystal structure perfection on the creep resistance of single crystal superalloys. The CMSX-4 and CMSX-4®Plus with increased Re content is analyzed. Single crystal rods are made by directional solidification process at the withdrawal rates 3 and 5 mm/min. The evaluation of microstructure and crystal structure perfection are carried out by light microscopy and X-ray diffraction Ω-scan methods. Creep tests are performed according to ASTM E-139-11 standard at the temperature of 982°C. Mathematical models for the creep resistance of the models are developed for both investigated superalloys. The influence of the crystal structure on the the investigated superalloys are built and the steady state creep rates are determined. Creep strength of both superalloys are compared. The results show that the CMSX-4®Plus nickel superalloy exhibits nearly two times higher creep resistance compared to the conventional CMSX-4 one.

In view of the excellent corrosion resistance and high temperature strength of TiVNbTa refractory high entropy alloy, and the potential application prospect of the TiVNbTa RHEA/Inconel 600 joining component, the diffusion bonding properties were studied. Diffusion joining of the two materials under conditions ranging from 850 ℃ to 1150 ℃ were carried out, the joints achieved at 850~1000 ℃ were submitted for microstructure examining, and the joints joined at all temperatures were used for shearing test. The results indicate that except for the joints obtained at 850 ℃, which only contain a lot of Ni-rich interface layers, all other joints have a multi-layer interface structure of "Inconel 600/Ni-based diffusion layer/Cr-rich layer/Ti-rich layer/Ni-rich layer/TiVNbTaNi (Fe, Cr) diffusion layer/TiVNbTa RHEA". The Ni-rich layer is a Ni2Ti type intermetallic compound with rhombohedral crystal structure, and the Cr-rich layer is a Cr2X type intermetallic compound with hexagonal crystal structure. The joint achieved at 950 ℃ has the highest shear strength, which is 357 MPa. The fracture mainly occurs in the weak interfacial area of Ni2Ti in the joint, and the crack propagates through the multi-layer interface. The analysis of the joints formation mechanism shows that during the diffusion joining process, Ti, V, Nb, and Ta atoms diffuse from the RHEA side to the Inconel 600 side, while Ni, Fe, and Cr atoms diffuse from the Inconel 600 side to the RHEA side. The diffusion of Ti and Ni atoms is intense. The segregation of Cr and Ni elements occurs under the driving source of interfacial chemical reactions. The diffusion of Nb and Ta atoms is hindered by the formation of Ni2Ti type interfacial layers, resulting in delamination.

Joining of dissimilar superalloys is indispensable in the field of advanced manufacture, achieving a high-quality joint while minimizing thermal damage to substrates during diffusion bonding is a critical but challenging pursuit. A low-temperature and rapid diffusion bonding strategy enabled by pulsed current was proposed to resolve this challenge. Attributed to the enhanced interfacial plastic-deformation and carbide-precipitation, pulsed current rapidly achieved a nanovoid-free and tight joint of GH3536 and GH5188 superalloys at a low temperature of 850 °C for 5 min. Meanwhile, the rapid joining process prevented the interfacial carbides from coarsening and allowed their elimination in a short-term heat-treatment. The carbide dissolution, recrystallization of highly-deformed grain and cross-interface grain growth during heat-treatment significantly enhanced the joint performance, the heat-treated joint exhibited a high ultimate strain of 25.5 % and a tensile strength comparable to the raw GH3536.

The high temperature oxidation resistance is crucial to assure the reliability of nickel-based superalloy parts serving at elevated temperature. Hastelloy X is a solid solution strengthening superalloy featured by decent mechanical properties and excellent high temperature oxidation resistance, having the potential to replace the commonly used nickel-based superalloy Inconel 718 in appropriate high-end manufacturing fields. In this work, a comparative study on mechanical properties and high temperature oxidation behaviour of Hastelloy X and Inconel 718 fabricated by laser directed energy deposition was carried out. Under the same processing parameters, the as-built Hastelloy X consisted of columnar and cellular γ phase with dispersed carbides, but Inconel 718 contained columnar γ phase with dispersed carbides and γ′ phase. At ambient temperature, Hastelloy X showed better ductility but inferior strength and hardness. Additionally, the isothermal oxidation tests at 1000 and 1100 °C demonstrated that the oxidation kinetics curves of both as-built superalloys followed the parabolic law. Hastelloy X owned a better high temperature oxidation resistance, which could be attributed to the uniformly distributed dense Cr2O3 and the relatively slight exfoliation of oxides in the oxide scales.

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.

During the production of single-crystal superalloy blades, a kind of channel-type defect, named “quasi-freckle”, was found on the casting surface, which is similar to typical freckles in macroscopic appearance but different in microstructure. In the as-cast microstructure of the quasi-freckle channels, the γ/γ’ eutectic is significantly accumulated and can be dissolved during the solution heat treatment. Since no disoriented grains were detected, the quasi-freckles have a basically identical crystal orientation with the matrix. The quasi-freckle channels actually appear as thermosolutal convection traces in the directional solidification process of single-crystal casting. Because the convection was not strong enough to break dendrite arms, the single-crystal consistency of the castings was not destroyed. However, with the deterioration of the solidification condition and the increase in solutal convection, quasi-freckles often develop into typical freckle defects.

Complex oxide–carbonitrides (MgO-Ti(CN), Al2O3-Ti(CN), and MgO·Al2O3-Ti(CN)) are the most common non-metallic inclusions presented in cast and wrought superalloys. In this work, a coupled kinetics model was proposed to predict the complex oxide–carbonitride inclusion’s precipitation behavior during the solidification of superalloys. This model takes into account thermodynamics, micro-segregation, heterogeneous nucleation in the inter-dendritic liquid, and growth controlled by the diffusion of solute elements and kinetics of interfacial reaction. The results demonstrated that both the cooling rate and nitrogen content take significant effects on the final size of complex oxide–carbonitride inclusions, as the former controls the total growth time and the latter determines the initial precipitation temperature. In comparison, the particle size of primary oxides shows a negligible impact on the final size of complex inclusions. The practice of an industrial vacuum arc remelting confirmed that the inclusion size variation predicted by the present model is reasonably consistent with the experimental results.

Co-precipitation of γ′ and γ′′ is the main strengthening mechanism that provides superior high-temperature strength in directly aged Alloy 718 aerospace parts. Control of their morphology, fraction, and configuration might allow exposure to more demanding operation environments in next-generation aircraft engines. The density of geometrically necessary dislocations introduced during hot deformation has been shown to significantly affect the co-precipitate morphology of γ′ and γ′′ in materials free of the δ-phase. However, the combined effects of geometrically necessary dislocation density and lower Nb content due to higher δ-phase fractions on co-precipitation behaviour and strengthening remain unknown. We verify these effects by hardness testing as a proxy for high-temperature strength in materials with 4.1 % δ-phase fraction. Deformation at 950 °C yields a remarkable increase of 12 % in hardness after direct ageing, explained by the prevalence of complex co-precipitate configurations. Deformation at 1000 °C decreases the δ-phase fraction and geometrically necessary dislocation density but achieves up to 19 % volume fractions of γ″, leading to a predominance of monoliths and duplet co-precipitates and a better direct ageing response. Atom probe microscopy reveals the flux of elements during co-precipitation. We recommend a δ-annealing treatment before the final forging step for manufacturing stronger Alloy 718 aerospace parts.

Abstract Evaluating and understanding the effect of manufacturing processes on the creep performance in superalloys poses a significant challenge due to the intricate composition involved. This study presents a machine‐learning strategy capable of evaluating the effect of the heat treatment process on the creep performance of superalloys and predicting creep rupture life with high accuracy. This approach integrates classification and regression models with domain‐specific knowledge. The physical constraints lead to significantly enhanced prediction accuracy of the classification and regression models. Moreover, the heat treatment process is evaluated as the most important descriptor by integrating machine learning with superalloy creep theory. The heat treatment design of Waspaloy alloy is used as the experimental validation. The improved heat treatment leads to a significant enhancement in creep performance (5.5 times higher than the previous study). The research provides novel insights for enhancing the precision of predicting creep rupture life in superalloys, with the potential to broaden its applicability to the study of the effects of heat treatment processes on other properties. Furthermore, it offers auxiliary support for the utilization of machine learning in the design of heat treatment processes of superalloys.

Hot deformation behaviour of Inconel X-750 superalloy was investigated using the hot compression test in the temperature range of 950–1150 °C and strain rate of 0.001–1 s−1. After excluding the effect of friction and adiabatic heating from obtained flow curves, three constitutive equations and processing maps were developed. The hyperbolic sine with an activation energy of 461 kJ. mol−1 could confidently predict the flow stress pattern of the alloy with a correlation coefficient (R) of 0.99 for both sub and super-solvus temperatures. The processing map also accurately depicts two domains with high values of power efficiency η greater than 34%. Among these, the temperature range of 1090–1150 °C and strain rates between 0.01–0.1 s−1 are optimum and safe to obtain a fully dynamically recrystallized (DRXed) structure. The microstructure of the other domain with a high η value has not depicted a recrystallized structure and the high-power efficiency value was associated with dynamic precipitation of gamma prime (γ′) at temperatures within the range of 980–1100 °C and strain rates lower than 0.01 s−1. Finally, the correlation between processing maps, flow curves and microstructural observations was analyzed authoritatively. The MC precipitation takes deformation into trouble in the temperature range of 1050–1100 °C and strain rates higher than 0.01 s−1 due to Zener drag pining effect.

A study on the film characteristics of a Cr2O3-forming nickel-based superalloy is conducted. A triplex structure is observed, in which Ta–Ti layer is developed between the external Cr2O3 and inner Al2O3 layer. When the exposure time increased, Ti atoms are divorced from the Ta–Ti layer, filling the voids inside the Cr2O3 layer, which improve the density of the external Cr2O3 layer and retard the inward penetration of the nitrogen. As a result, the degree of internal nitrides is reduced. Consequently, the synergy effect of Ta and Ti in the Cr2O3 forming alloy is beneficial to improve the oxidation resistance.

This study investigates the microstructural evolution and its effect on the fatigue performance of a novel nickel-based powder superalloy FGH4113A (WZ-A3) after long-term aging at 760 °C and 815 °C. The results show that long-term aging both at 760 °C and 815 °C has no significant effect on the grain size and morphology of the alloy. After aging at 760 °C for up to 2020 h, the size of the γ′ phase remains unchanged, and its morphology transitions from nearly square to nearly spherical. During long-term aging at 815 °C for 440 h, γ′ phase coarsening and spheroidizing occur simultaneously. With prolonged aging time, the size and spheroidization degree of the γ′ phase further increase. During long-term aging up to 440 h at 760 °C, the dispersed granular MC and M6C carbides dissolve and re-precipitate. By 2020 h of aging, flocculent carbides precipitate and non-continuous M6C and M23C6 accumulate at grain boundaries. After long-term aging at 815 °C for 440 h, flocculent carbides begin to precipitate within the grains. By 2020 h of aging, a large amount of flocculent carbides precipitate with significant coarsening and enrichment of the grain boundary carbides. Due to the insignificant coarsening of the γ′ phase as well as the enrichment and precipitation of the grain boundary carbides, the fatigue performance of the alloy decreases slightly after long-term aging.

The water-assisted laser trepanning method has been proven to improve the quality of laser drilling; however, the effect of water temperature on this process is currently unclear. In order to investigate the influence of water temperature on the quality of holes produced via water-assisted laser trepanning in superalloys, this study used the controlled variable method to investigate the effects of three water temperatures—low temperature (2 °C), normal temperature (20 °C), and high temperature (70 °C)—on the following factors: spatter, hole diameter, taper angle, hole sidewall morphology, and recast layer. The results show that the spatter around the hole reduced, the hole entrance/exit diameter increased, and the roughness of the hole’s sidewall decreased with an increase in single-pulse energy. However, the effect of single-pulse energy on the recast layer was not obvious. As the temperature of the water increased, the hole entrance/exit diameter increased, and the roughness of the hole’s sidewall decreased. When the single-pulse energy was 1.0–1.9 J, using a lower water temperature produced a hole with a smaller taper angle. Compared with a water temperature of 20 °C, the movement of the melt film on the hole’s sidewall accelerated when the water temperature was 70 °C; as a result, more molten material could be removed from the hole, resulting in a decrease in the thickness of the recast layer. However, when the water temperature was 2 °C, the heat-affected zone and the thickness of the recast layer decreased more significantly. The results of this study provide technical support for the optimization of water-assisted laser drilling.

The microstructure and 650 °C tensile properties of a compositionally graded IN718-René41 (718-R41) superalloy fabricated by laser blown-powder directed energy deposition (DED-LB/M) are investigated to understand structure–property relationships and baseline tensile properties. Digital Image Correlation (DIC), in situ neutron diffraction, and conventional characterization techniques are performed to study the as-built and heat-treated states. The applied heat treatment generates static recrystallization and equiaxed grains in 718-rich compositions, while R41-rich compositions remain partially or un-recrystallized possibly influenced by a higher MC carbide fraction (>0.5%). The yield strengths of the 718 and R41 sections in the heat-treated state are comparable to wrought forms but the graded compositions show weakness due to unoptimized heat treatment. Diffraction elastic constants first decrease and then increase along the 718-R41 composition gradient, while a small difference is observed between the as-built and heat-treated states and γ, γ′ phases. Overall, the compositionally graded region shows a smooth transition in the elastic properties. Grain-level load transfer from the (220) to (200) grains shows compositional dependence, and qualitatively agrees with DIC-measured macroscopic yield strength. Within the (200) grains, the γ/γ′ phases deform elastically until the γ phase yields and afterwards, the γ′ phase takes load from the γ phase.

The Inconel 718 superalloy demonstrates the potential to fabricate high-temperature components using additive manufacturing. However, additively manufactured Inconel 718 typically exhibits low strength, necessitating post-heat treatments for precipitate strengthening. This study investigated the microstructures and mechanical properties of the Inconel 718 superalloy fabricated via laser powder bed fusion. The room-temperature and high-temperature tensile properties of the Inconel 718 alloy samples following various post-heat treatments were evaluated. The results indicate that the as-built samples exhibited columnar grains with fine cell structures. Solution treatment resulted in δ phase formation and grain recrystallization. Subsequent double aging led to finely distributed nanoscale γ′ and γ″ particles. These nanoscale particles provided high strength at both room and high temperatures, resulting in a balanced strength and ductility comparable to the wrought counterpart. High-temperature nanoindentation analyses revealed that the double-aging samples exhibited very high hardness and low creep rates at 650 °C.

The paper investigates various methods of microfinishing and arrives at the best technique to produce a very smooth surface. Various setups, with and without oscillation, were developed, together with a microfinishing attachment used on conventional lathes and milling machines. The workpiece material used was an amorphous nickel–phosphorus Ni–P alloy. The surface roughness parameters, such as Sa, Sv, and Sp, were measured with the TalySurf CCI6000 instrument. For the measurement of the surface protrusions, an “analysis of islands” technique was used at various levels of cut-off. The 2BA method—machining below the workpiece axis with oscillation—turned out to be the most effective method applied because it had the highest density of protrusions while having the smallest value of surface roughness. Non-oscillation with the machining zone below the axis also becomes effective, indicating that repositioning can compensate for a lack of oscillation. Already, the very compact surface structure achieved with minimized depths in the valleys by the 2BA method supported the improvement in tribological performance and increase in load-carrying capacity, together with lubricant retention enhancement. These results show that the microfinishing process can be optimized by parameter tuning, and also, non-oscillating methods could come to be a practical alternative, probably reducing the complexity of equipment and cutting costs. Further studies need to be aimed at the scalability of these methods and their application to other materials and fields.

A combined stamping–bulging forming process was proposed to achieve high-precision forming of large-diameter, ultra-thin-walled, superalloy welded S-type corrugated diaphragms. The underlying principle is to enhance the diaphragm’s forming accuracy by increasing the plastic deformation region and reducing springback. Using the ABAQUS version 6.14 finite element analysis software, finite element models were constructed for the stamping, hydraulic bulging, and combined stamping–bulging forming processes of the welded S-type metal corrugated diaphragms. A comparative analysis was conducted on the forming processes of the welded S-type metal corrugated diaphragms under the three forming methods, focusing on equivalent stress, distribution of wall thickness, and forming accuracy. This analysis determined the optimal forming process and the corresponding process parameters for superalloy welded S-type metal corrugated diaphragms. The results show that under a constant drawing force, as the bulging pressure increases, the plastic deformation of the straight sections of the diaphragm becomes more pronounced, resulting in improved shape accuracy. The combined stamping–bulging forming process guarantees the highest degree of shape accuracy for the diaphragm. The optimal process parameters were identified as a 30 t force and a 5 MPa pressure, with a maximum shape error of 0.02 mm. Concerning a plate thickness of 0.3 mm, the maximum deviation rate was found to be 6.7%, which represents a 30% improvement over traditional stamping processes. The maximum wall thinning rate was found to be 3.3%, a 1% reduction compared to traditional stamping processes, confirming the process’s feasibility.

Ru is crucial in improving creep properties in Nickel-based single-crystal superalloys. The effect of Ru content on the creep behavior of nickel-based single-crystal superalloy was studied. Ru exhibits unprecedented mechanical properties, increasing the creep life at 1120 °C but decreasing it at 1180 °C. This is due to the competition in the stress concentration formed between the topologically close-packed phases and the creep cavity. They are both related to the dissociation of the γ′ phase. The effect of oxidation caused by the addition of Ru is lower than these two factors. This work helps to recognize the comprehensive effect of Ru and can provide guidance for alloy design in the future.

The interfacial microstructures and corrosion behavior of tungsten heavy alloy/superalloy dissimilar joints brazed with various Cu–Ti based multicomponent amorphous alloys were investigated by time-varying chemical bath immersion tests and electrochemical measurements. The longitudinal analysis of corrosion behavior differences in different regions of dissimilar joints was conducted, and the horizontal analysis of the influence of compositional variation in filler materials on corrosion behavior was investigated. Importantly, the brazed joint with CuTiNiZrV filler material (CT3 joint) exhibited the noblest Ecorr (−0.911 VSCE) and the highest charge transfer resistance (1610.5 Ω cm2). From the compositional and microstructural effects on the corrosion resistance, the enhancing anti-corrosion performance was mainly attributed to the tailoring of the microstructures and corrosion potential of the brazing seam, and the formation of protective compact oxide film (Fe2O3-NiO-CoO-VO).

In order to study the influence of the vacuum arc remelting process (VAR) on the grain structure of the ingot and provide initial condition for the prediction and analysis of the subsequent process such as homogenization and billet forging, an efficient and accurate three-dimensional (3D) cellular automata method was developed for the VAR process, and all parts of the algorithm were rigorously verified, and it can be combined with the MeltFlow-VAR. An ingot of 718 alloy was smelted through experiment for calculation verification and proved the accuracy of the predictions. A new method for discretization of Euler angles to obtain orientation index is proposed and verified, which is more flexible and higher computationally efficient than previous algorithms. Aiming at the problem of a large number of cells and calculation time on large-scale VAR ingot in the future, a hybrid parallel scheme is designed, and it is expected to realize large-scale calculations on the supercomputer system. Finally, the effect of different cell sizes on the calculation results was also studied, and the grain size at the edge of the ingot was not affected by the cell size.

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.

Since fatigue cracks nucleate and initiate generally at the surface of the rotary components such as blades and discs, the surface condition is the most important factor affecting the fatigue life. Surface scratches are suitable sites for stress concentrations and therefore the nucleation stage of fatigue cracks will be shortened. In the present work, the influence of surface roughness on the low cycle fatigue life behavior of nickel-based superalloy Rene®80 at the temperature of 900°C was evaluated. Results of low cycle fatigue tests (LCF) under strain-controlled condition at 900°C for R = εmin/εmax = 0 and strain rate of 2×10 –3 s –1, at a total strain range of 1.2% showed an inverse relationship between fatigue strength and surface roughness of the specimens. In this study, increasing the surface roughness of Rene®80 from 0.2 μm to 5.4 μm led to the decline in the final LCF life from 127 cycles to 53 cycles which indicated a 58.3% reduction in fatigue life at the same condition. Fractography evaluation also exhibited that fatigue cracks initiated from the notch in the rough specimens, whereas in the smooth specimen fatigue cracks nucleated from the internal imperfections and carbides.

Gradient MCrAlY coatings exhibited good oxidation resistance during cyclic oxidation at 1200 °C. The interdiffusion behavior between the coating and substrate at 1200 °C exhibited distinct differences compared to that below 1100℃. In this study, the interdiffusion behavior in the gradient MCrAlY/superalloy system was investigated at 1080 °C/1200 °C after cyclic oxidation. To exclude the effect of aluminization on diffusion behavior, interdiffusion behavior between MCrAlY coatings and nickel-based superalloys was also studied at 1080 °C/1200 °C under oxygen-free condition. Based on experiment and thermodynamic calculation, temperature-dependent interdiffusion relationships between Al and Cr were established. The results showed that the diffusion fluxes of Al and Cr were close at 1080 °C. The diffusion flux of Cr could exceed that of Al at 1200 °C, resulting in the formation of the Cr-rich γ phase. The secondary γ' phases precipitated during the cooling of Cr-rich γ phase from 1200 °C. Furthermore, the calculations indicated that increasing Cr in the substrate reduced the diffusion driving force of Al from coating to substrate. This study clarified the role of Cr in interdiffusion and proposed a strategy to reduce the precipitation of TCP phases in gradient MCrAlY/superalloy system at 1200 °C by designing a wide Cr-rich γ phase zone.

Joining single crystal superalloy with polycrystalline superalloy has important applications in the aerospace industry. Here, the IC10 single crystal superalloy to GH536 polycrystalline superalloy was diffusion brazed using a BNi-2 filler alloy. The effects of bonding temperature and time on the microstructure evolution and mechanical properties of the GH536/IC10 joints were investigated in detail. The results elucidated that the joint brazed at a lower temperature and time (i.e., 1050 °C/30min) was composed of diffusion affected zone (DAZ), athermal solidification zone (ASZ), and isothermal solidification zone (ISZ). The secondary precipitates formed in DAZ were Cr-rich borides, Cr–Mo borides, and Cr–Mo–W borides. The ASZ was made up of Cr-rich borides, Ni-rich borides, Ni–Cr borides, and Ni-based solid solutions. These borides with high hardness were the potential source of cracks and caused the joints to fracture under a lower load. Raising bonding temperature and time gradually eliminated Ni-rich borides in ASZ and Cr-rich borides in DAZ, and improved the shear strength.