The elevated pouring temperatures characteristic of nickel-based superalloys usually result in a diminished efficacy of intermetallic grain refiners in their refinement capabilities. The Thermally Controlled Solidification (TCS) technique employs an extremely low pouring temperature, thereby enabling the practical utilization of such refiners. This study elucidates the grain refinement mechanism of CrFeNb and Co3FeNb2 intermetallic refiners in the IN939 superalloy under TCS conditions. After the addition of refiners, the average grain size markedly decreased from 6981 μm to 129 μm. The in-situ formation of the C14 Laves phase on refiner particles serves as the primary heterogeneous nucleation site. A specific crystallographic orientation relationship (OR) between the C14 Laves phase and the γ matrix was identified through Kikuchi patterns and electron backscatter diffraction (EBSD) analysis: [101]γ // [101̅0]Laves, (1̅11)γ // (2̅112)Laves. Edge-to-Edge Matching (E2EM) calculations corroborate the superior nucleation capability of the C14 Laves phase. Moreover, the refiners possess high stability and effectively homogenize the microstructure of complex castings. This study introduces a refinement mechanism for intermetallic refiners and offers theoretical insights to inform the development and application of innovative grain refiners for nickel-based superalloys.

Nickel-based superalloys play a vital role in advanced aero-engines and gas turbines due to their exceptional high-temperature strength, oxidation resistance, and microstructural stability. The high content of alloying elements in these nickel-based superalloys significantly improves their strength, creep resistance and oxidation performance. This review summarizes the roles of various alloying elements in solid solution strengthening, precipitation strengthening and grain boundary reinforcement in nickel-based superalloys. Nevertheless, challenges such as elemental segregation during fabrication and limitations in high-temperature performance have hindered their widespread application. Therefore, microstructural evolution mechanisms during thermal deformation and the effects of heat treatment—including homogenization, solution treatment, and aging—on conventional and additively manufactured alloys are analyzed. The improvement of the high-temperature stability of nickel-based superalloys through improving the microstructure by the incorporation of ceramic particles is also discussed. In addition, high-throughput computing and machine learning-assisted design of alloy composition provide a new approach for achieving superalloys of high performance is emphasized. It is expected that this review will provide valuable guidance for the development of high-efficiency, high-performance nickel-based superalloys.

Adhesive deficiency, characterized by incomplete or insufficient adhesive application, is a common manufacturing defect in bonded structures. This study systematically investigates the impact of adhesive deficiency on the strength and durability of aluminum alloy adhesive joints through combined experimental and finite element analysis. The results demonstrate that joint strength is significantly influenced by the area, location, and dispersion of adhesive deficiency. Strength degradation increases with larger deficient areas, with reductions ranging from 12.7% with 10% deficiency at the front edge to 48.3% with 40% deficiency at the center. The location of deficiency follows the performance order: front edge > angle corner > side edge > center. Simulations show good agreement with experiments, with errors of about 5%. Additionally, under a fixed deficiency area, dispersed defects, such as two discrete zones, result in better strength retention than concentrated ones. Environmental aging tests further reveal that proper defect location and dispersion help mitigate long-term strength degradation. These findings provide valuable guidance for optimizing adhesive joint design and assessing defect tolerance in practical applications.

Through dual-defect engineering, a 2D/2D heterojunction composed of nitrogen-deficient-rich g-C3N4 and oxygen-deficient TiO2 (DCN/DTiO2) was successfully constructed. Comprehensive characterization reveals that the heterojunction possesses well-defined layered architecture with enhanced specific surface area, extended light absorption range, and remarkably facilitated charge carrier separation and migration. The synergistic effects between dual defects and 2D/2D interface significantly boost the photocatalytic activity. Consequently, the optimized 25 wt% DCN/DTiO2 achieves a stable hydrogen evolution rate of 2.80 mmol/g/h over 6 h and completes 93% tetracycline degradation within 60 min, providing an effective design strategy for highperformance bifunctional photocatalysts.

Magnesium alloys are promising lightweight structural materials because of their low density and high specific strength, but their hexagonal close-packed structure leads to limited room-temperature ductility and pronounced anisotropy. This review summarizes the multi-stage roles of rare-earth elements in grain refinement and microstructural stability of magnesium alloys, and identifies 3–8 μm as a representative fine-grained range frequently associated with favorable strength–ductility coordination. Grain size governs the deformation-carrying mode and plastic accommodation by redistributing the contributions of twinning, slip, precipitation, and grain-boundary effects. Rare-earth elements act continuously during solidification, solid-state processing, and thermomechanical deformation through grain boundary segregation, precipitate pinning, and dynamic recrystallization control, while also contributing to texture weakening. The stability of this fine-grained platform is further constrained by temperature, component scale, and service time. Even under low rare-earth conditions, however, microstructural synergy remains achievable through process optimization, precipitate homogenization, and dynamic recrystallization regulation. Overall, this work clarifies the scientific basis of fine-grain strengthening in Mg–RE alloys from the perspectives of grain-scale control, mechanism redistribution, precipitation–texture–grain boundary coupling, and engineering boundary conditions, providing theoretical support and practical guidance for the design of high-performance, low-rare-earth lightweight magnesium alloys.

Ni-based superalloys represent a critical class of advanced materials in modern industry especially for the fabrication of hot-section components in aero-engines and aerospace propulsion systems. These alloys typically exhibit excellent oxidation resistance, creep resistance and corrosion resistance under high-temperature conditions, making them a cornerstone of modern industrial technology. The performance of Ni-based superalloys lies in controlling their precipitation phases. Common precipitations include gamma ' phase, gamma '' phase, carbides, and TCP phases, where the gamma ' phase serves as the primary reinforcing phase. The size, morphology, distribution, and volume fraction of gamma ' precipitates strongly influence creep resistance, strength, and deformation behavior. Existing studies have generated substantial knowledge on alloy design, processing, and service behavior. However, a gamma '-centered synthesis that integrates precipitation, regulation, and degradation remains limited. This paper comprehensively reviews the precipitation mechanisms of the gamma ' phase in Ni-based superalloys, the factors affecting its characteristics, and its failure behavior under service conditions. The aim is to clarify the role of the gamma ' phase in these alloys and to provide theoretical guidance for their further development.

Co-Al-W-based alloys have been recognized as promising next-generation structural materials for high-temperature applications due to the formation of the γ′ strengthened phase. However, optimizing these superalloys through experimental studies is a significant challenge because of complex element interactions. This paper investigates the temporal processing and mechanisms of γ′ precipitates in novel Co-based superalloys using the phase-field method. By coupling the calculation of phase diagrams (CALPHAD) approach for the phase free energy and chemical mobility involving element interactions, and by calculating thermophysical parameters of alloys using first-principles, we developed a quantitative phase-field model for multicomponent systems. Using this model, the element diffusion path and γ′ evolution path are simulated in ternary diffusion couples and aging alloys, and the results align well with experimental observations. Furthermore, the effects of W content in Co-Al-W alloys on the coarsening kinetics and mechanisms of γ′ precipitates during long-term aging are systematically studied. It is found that increasing W content results in higher γ′ volume fraction and increased γ′ coarsening rate. The accelerated coarsening is primarily attributed to the shortened inter-particle spacing between γ′ precipitates, which is comprehensively analyzed through element diffusion distance and flux. Additionally, the model is extended to quaternary systems and successfully applied to Co-Ni-Al-W alloy. This study provides a novel method for the quantitative prediction of γ/γ′ microstructures and contributes to the alloy design and processing optimization of novel superalloys.

The effect of 3 wt% Ru addition on the recrystallization behavior of a Ni-based single crystal superalloy was systematically investigated. The results revealed that Ru addition significantly promoted the microsegregation of Al and Ta elements into the interdendritic region during solidification, leading to an increased volume fraction of gamma/gamma ' eutectic from 6.67% in the Ru-free alloy to 9.5% in the 3Ru alloy. These enlarged eutectic regions, which exhibited lower deformation resistance than the dendrite cores, acted as preferential sites for strain concentration during indentation deformation, resulting in a larger deformation zone with higher dislocation density beneath the indentation in the 3Ru alloy. Upon subsequent heat treatment at 1315 degrees C, the recrystallization preferentially nucleated within these highly deformed gamma/gamma ' eutectic areas via the particle stimulated nucleation (PSN) mechanism. Consequently, the alloy with 3 wt% Ru additions exhibited a larger recrystallized area and coarser recrystallized grains compared to the Ru-free alloy. This work demonstrated that Ru addition promoted PSNmediated recrystallization nucleation by increasing the gamma/gamma ' eutectic content at as-cast and enhancing deformation localization.

Interface engineering via trace boron (B) doping was utilized to improve the creep performance of a fourth-generation single crystal (SX) superalloy. The effects of 40 ppm B addition on microstructural evolution and the underlying strengthening mechanisms were systematically investigated by three-dimensional atom probe tomography (3D-APT) and transmission electron microscopy (TEM). For the first time, the study found that B segregation at the γ/γ′ interface increased the creep life from 181.18 h to 241.31 h under 1100 °C/150 MPa. Detailed 3D-APT analysis revealed that B doping increased the γ/γ′ lattice misfit by altering the elemental distribution between the γ matrix and γ′ phase, thereby accelerating the formation of dense dislocation networks during the primary creep stage. Meanwhile, the segregation of Re, Co and Mo in the γ matrix ensured the integrity of the γ′ rafts during creep. The synergistic effects of the above two mechanisms improved the secondary creep life by 45.8%. Furthermore, first-principles calculations demonstrated that B segregation at the γ/γ′ interface reduced interfacial free energy and strengthened interfacial bonding, which stabilized the γ/γ′ interface and suppressed the TCP phases growth. As a result, crack initiation was reduced and the tertiary creep life was prolonged by 23.9%.

This study systematically investigated the twinning transformation mechanism of topologically close-packed phases (μ phases) in a Ni-based single crystal superalloy during creep deformation. Two distinct types of twins were identified in the μ phase: misaligned (TB1-type) and symmetric (TB2-type) twins. The formation of the TB1-type twin occurred when shear stress acted along the [1¯101]μ direction within the (011¯2)μ crystal plane of the μ phase, initially generating stacking faults, which subsequently evolve into a TB1-type twin structure through atomic rearrangement. Interestingly, the transformation of TB2-type twins followed two separate pathways: (1) further shear deformation of TB1-type twins along the [1¯101]μ direction within the (011¯2)μ plane under external stress; (2) structural retention of P phase configurations resembling TB2-type twin boundaries during the P→μ phase transformation. These findings provide fundamental insights into the relationship between TCP phase transitions and creep behavior, offering valuable theoretical guidance for the design of advanced superalloys.

The gradient refinement mechanism of mixed intermetallic particles on equiaxed K492M superalloy was studied. The grain size of K492M superalloy added with mixed intermetallic (CrFeNb and Co3FeNb2) particles could be obviously refined from 3132.89 mu m to 608.51 mu m while the separate intermetallic (CrFeNb or Co3FeNb2) particles led to little refinement. This superior refinement performance was attributed to the synergistic effect of the mixed particles in promoting the formation of highly potent Ni9Nb phases at the interfaces between the gamma matrix and the intermetallic particles. Based on Edge-to-Edge model (E2EM) and orientation identification, the lattice misfit between the gamma matrix and Ni9Nb was about 0.27% with the orientation relationship: (200)gamma || (200) Ni9Nb, [001] gamma || [001] Ni9Nb. A gradient refinement mechanism was proposed to elucidate the role of mixed intermetallic particles. Both intermetallic particles facilitated the formation of Ni9Nb acting as the nucleation sites. However, CrFeNb particles preferentially formed Ni9Nb due to a higher thermodynamic driving force, followed by Co3FeNb2. Consequently, the mixed intermetallic particles provided a greater density of nucleation sites compared to separate additions, leading to enhanced grain refinement.

The dendrite growth behavior in DD3 single crystal blades under different secondary orientations was investigated. Microstructural analysis revealed a significantly smaller primary dendrite arm spacing (PDAS) in the blade body for the [210] orientation compared to the [100] orientation. For [210] orientation single crystal blades, the angle between the heat flow and the secondary dendrite arms was larger than the [100] orientation blades, causing a more complex dendrite growth path. Furthermore, melt flow induced lateral dendrite growth, promoting higher-generation branching during solidification. In addition, when the angle between the solute diffusion direction and temperature gradient changed, severe solute segregation occurred in [210] orientation, further leading to changes in the local undercooling and freezing range, which resulted in a decrease in PDAS. In other words, compared to [100] orientation, the decrease in PDAS of single crystal blades with [210] orientation was attributed to the synergistic effects of the dendrite growth path and solute element distribution during solidification process.

Magnesium alloys hold considerable promise for lightweight structural applications due to their low density and high specific strength. However, their intrinsic hexagonal close-packed crystal structure results in a limited number of active slip systems, inadequate high-temperature strength, poor creep resistance, and pronounced flammability. These inherent drawbacks significantly restrict their utilization in demanding high-temperature and severe service environments, such as those encountered in aerospace and transportation sectors. To overcome these performance limitations, alloying with rare earth elements has proven to be an effective strategy. This article provides a detailed analysis of the regulatory effects and underlying mechanisms by which rare earth elements influence the microstructure of magnesium alloys. It further examines the critical roles and mechanisms by which RE additions significantly enhance properties such as creep resistance, superplasticity, fatigue life, and flame retardancy. The discussion also extends to the synergistic effects achieved by composite alloying with elements such as Al, Zn, and Ag, or by the incorporation of nanoparticle/metallic particles, which collectively contribute to multiple strengthening mechanisms. Future research should focus on the design of Mg alloys with low or even zero heavy rare earth content, the in-depth elucidation of multiscale structure-property relationships, the integration of advanced processing technologies, and the development of lifetime prediction models under extreme environments. These efforts will be essential for promoting the reliable application of magnesium alloys in a wider range of high-temperature structural scenarios.

In this study, effects of aging at 750 °C for 250 h on microstructure, micromechanical and macromechanical properties of CoCrFeNiTa0.43 eutectic high entropy alloy were investigated in detail. After aging at 750 °C for 250 h, Ni, Ta-rich γ''-Ni3Ta phases with body-center tetragonal (BCT) structure precipitated from γ matrix. After aging, microhardness of CoCrFeNiTa0.43 alloy increases ∼2.5%. Meanwhile, room temperature compression tests indicated that aged CoCrFeNiTa0.43 alloy exhibited higher 0.2% yield strength than as-cast CoCrFeNiTa0.43 alloy (increased from 1068 MPa to 1340 MPa, i.e. increasing 25.5%), and aged CoCrFeNiTa0.43 alloy also maintained relatively high plasticity (with fracture strain>13%). The strengthening effect of γ''-Ni3Ta phases was mainly attributed to Orowan bypass mechanism, and the contribution of γ''-Ni3Ta phases to 0.2% yield strength was calculated to be 412.2 MPa by using the Orowan bypass model. Moreover, as compared with other eutectic high entropy alloys, aged CoCrFeNiTa0.43 alloy exhibited a relatively high yield strength and relatively high fracture strain.

Eutectic high-entropy alloys (EHEAs) have attracted significant attention due to their excellent strength-ductility synergy under quasi-static tensile loading. This favorable mechanical performance has intuitively led to the assumption that EHEAs also possess high fracture toughness, given their capacity for substantial plastic energy absorption during deformation. In this study, we decouple tensile ductility and fracture toughness in a dual-phase AlCoCrFeNi2.1 EHEA produced via laser powder bed fusion. Experimental results demonstrate that this EHEA exhibits excellent tensile behavior with a yield strength of 1320 MPa, a tensile strength of 1590 MPa and a uniform elongation of 10.5 %. Paradoxically, this EHEA exhibits a relatively low fracture toughness of 39 MPa m1/2. Fractographic analysis reveals a largely brittle fracture process, wherein the fatigue pre-crack propagates nearly straight with limited evidence of dislocation-mediated plasticity at the crack tip. Crack propagation is facilitated by microcracks that form at the phase boundaries and coalesce with the main crack along the lamellar direction. This embrittled behavior contrasts sharply with the coordinated deformation observed in both face-centered cubic (FCC) and body-centered cubic (BCC) phases during uniaxial tensile loading. Crystal plasticity simulations under varying stress states reveal that the local stresses within the FCC and BCC phases increase substantially under high stress triaxiality (i.e. with a pre-crack), reaching values approximately four times higher than those under low stress triaxiality condition (i.e. uniaxial tension). Such elevated local triaxial stress impedes dislocation slip across phase boundaries, promoting rapid crack propagation with minimal plastic deformation.

Nickel-based eutectic composites exhibit excellent high-temperature mechanical properties arising from the synergistic strengthening of carbide fibers and γ′ precipitates. However, the as-cast microstructures of composites contain coarse γ′ precipitates which significantly limit their high-temperature strength. While heat treatment is effective for refining γ′ phase, the concomitant carbide transformations and synergistic control of γ′ and carbides remain unclear. This study investigates the microstructural evolution during heat treatment and clarifies the mechanisms for enhanced high-temperature tensile properties. The results show that coarse γ′ phases formed during solidification can be completely dissolved during solution treatment at temperatures above 1300°C. Meanwhile, M6C carbides precipitate at grain boundaries, via two distinct pathways: MC decomposition and direct precipitation from γ matrix. Subsequent aging at 870°C promotes precipitation of fine γ′ phases and triggers the formation of Cr-enriched M23C6 carbides at grain boundaries through direct precipitation from the γ matrix. Tensile testing at 900°C reveals that the optimized heat-treatment enhances tensile strength by 12.2% and yield strength by 22.2% compared to the as-cast condition. This improvement originates from the precipitation strengthening by refined γ′ precipitates, grain-boundary strengthening by carbides, and a transition in dislocation–precipitate interactions from dislocation entanglement to Orowan bypassing and shearing of γ′ phase.

In this investigation, effects of substituting Mo for W and temperature on lattice constants of gamma and gamma ' phases and gamma/gamma ' misfits of second generation Ni based single crystal superalloys was investigated. The lattice constants of gamma and gamma ' phases in heat-treated W-rich and Mo-rich single crystal superalloys were measured by in-situ high temperature X-ray diffraction (HT-XRD) at temperature ranged from room temperature to 1150 degrees C. Meanwhile, both thermodynamic calculation and Vegard's law (considering thermal expansion coefficient) were used to calculate lattice constants of gamma and gamma ' phases and gamma/gamma ' misfits of two experimental alloys. Both experiment and calculation results indicated that substituting Mo for W obviously increased lattice constant of gamma phase, while its influence on lattice constant of gamma ' phase was limited, and thus substituting Mo for W significantly decreased gamma/gamma ' misfit. Meanwhile, the experimental results of HT-XRD indicated that absolute value of gamma/gamma ' misfits of two experimental alloys at 1100 degrees C were higher than those of at 1150 degrees C, which was in good agreement with evolution rule of gamma/gamma ' interfacial dislocation network spacings in two experimental alloys (after creep rupture at 1100 degrees C and 1150 degrees C).

Nickel-based single-crystal(SX)superal-loys are key materials used for turbine blades.With the increase in turbine inlet temperatures,continuous improvement in the creep rupture life is a major target for developing the next generation of SX superalloys.Currently,the design of SX superalloys primarily depends on the rhe-nium(Re)and ruthenium(Ru)contents.

A 22% variation in creep life was found at 950 degrees C/245 MPa in single-crystal blades with different secondary orientations. In the experimental and simulation results, it was seen that the movement of {111} <110> dislocations had caused the formation of the initial square micropores, which further led the crack to extend along the <110> orientation. The different secondary orientations had resulted in varied paths required for the crack to penetrate the specimen. At last, a model was constructed to clarify the action mechanism of the secondary orientation on creep life for single-crystal blades. [GRAPHICS] .