Search Results (468)

Based on molecular dynamics simulation, we conducted a comprehensive study on the tensile behaviors and properties of the $\gamma$(Ni)/${\gamma }^{\prime }$(Ni₃Al) superalloy with varying ${\gamma }^{\prime }$(Ni₃Al) phase volume fractions ($V\left({\gamma }^{\prime }\right))$ under high-temperature, high-strain-rate service environments. Our investigation revealed that the tensile behavior of the superalloy depends critically on the $V\left({\gamma }^{\prime }\right)$. When the $V\left({\gamma }^{\prime }\right)$ increased from 13.5 to 67%, the system’s tensile strength exhibited a non-monotonic response, peaking at $\mathrm{V}\left({\gamma }^{\prime }\right)$ = 40.3% before progressively decreasing. Conversely, the maximum uniform plastic strain decreased linearly and significantly when $V\left({\gamma }^{\prime }\right)$ increased. These results establish an atomistically informed framework that elucidates the composition–microstructure–property relationships in $\gamma$(Ni)/${\gamma }^{\prime }$(Ni₃Al) superalloys, specifically addressing how $V\left({\gamma }^{\prime }\right)$ governs variations in deformation mechanisms and mechanical performance. Furthermore, this work provides quantitative design paradigm for optimizing ${\gamma }^{\prime }$(Ni₃Al) precipitate architecture and compositional tuning in the Ni-based $\gamma$(Ni)/${\gamma }^{\prime }$(Ni₃Al) superalloy. Full article

GTD 111 has been employed in first-stage blades in different gas turbines. The study of microstructural evolution is essential for the lifetime assessment and development of turbine blades. The microstructural stability of a 130 MW gas turbine first-stage blade at 800 °C was studied. The microstructure’s evolution was analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermodynamic calculation. As thermal exposure time increases, the shape of γ′ precipitates changes from square to spherical. During thermal exposure, MC particles formed and coarsened along the grain boundaries, and primary MC carbide decomposed into the η phase and M₂₃C₆. The stability of MC carbide at the grain boundaries was lower than that within the grains. MC carbide precipitated at the grain boundaries tends to grow along the boundaries and eventually forms elongated carbide. High-resolution transmission electron microscopy (HRTEM) images indicate that the orientation of the γ′ precipitate changes during the coarsening process. The GTD 111 alloy can be deformed through dislocation shearing at 800 °C. The hardness value initially increases, then decreases with further exposure, which is related to the reduced precipitation strengthening by γ′ precipitates and the reduction in the hardness of the γ matrix. Full article

Molybdenum alloys as refractory alloys can provide strength levels at operating temperatures higher than that of Ni-base superalloys, yet their ductility is usually inferior to Ni-base alloys. Currently, commercialized Mo alloys are much fewer than Ni alloys. The motivation of this work is to explore opportunities of discovering useful alloys from the usually less investigated binary Mo-X systems (X = alloying element). With computational thermodynamics (CALPHAD), first-principles calculation, and mechanistic modeling combined, in this work a large number of Mo-X binary systems are investigated in terms of thermodynamic features and mechanical properties (yield strength, ductility, ductile-brittle transition temperature, creep resistance, and stress-strain relationship). The applicability of the alloy systems as solution-strengthened or precipitation-strengthened alloys is investigated. Starting from 92 Mo-X systems, a down-selection process is implemented, the results of which include three candidate systems for precipitation strengthening (Mo-B, Mo-C, Mo-Si) and one system (Mo-Re) for solid-solution strengthened alloy. In a composition optimization of Mo alloys to reach the properties of Ni-base superalloys, improving ductility is of top priority, for which Re plays a unique role. The presented workflow is also applicable to other bcc refractory alloy systems. Full article

The slurry aluminizing process is widely employed to enhance the oxidation and corrosion resistance of nickel-based superalloys used in high-temperature environments such as gas turbines and aerospace engines. This study investigates the effects of the concentration of Al vapors in the reactor chamber and the initial slurry layer thickness on the microstructure, chemical composition, and phase composition of aluminide coatings. Coatings were manufactured on Ni-based superalloy substrates using CrAl powders as an aluminum source and chloride- and fluoride-based activator salts. The effect of the initial thickness of the slurry layer was studied by varying the amount of deposited slurry in terms of mg_slurry/cm²_sample (with constant mg_slurry/cm³_chamber). The microstructure and phase composition of the produced aluminide coatings were evaluated by SEM, EDS, and XRD analysis. Slurry thickness can affect concentration gradients during diffusion, and the best results were obtained with an initial slurry amount of 100 mg_slurry/cm²_sample. The effect of the Al vapor phase in the reaction chamber was then investigated by varying the mg_slurry/cm³_chamber ratio while keeping the slurry layer thickness constant at 100 mg_slurry/cm²_sample. This parameter influences the amount of Al at the substrate surface before the onset of solid-state diffusion, and the best results were obtained for a 6.50 mg_slurry/cm³_chamber ratio with the formation of 80 µm coatings (excluding the interdiffusion zone) with a β-NiAl phase throughout the thickness. To validate process flexibility, the same parameters were successfully applied to produce platinum-modified aluminides with a bi-phasic ζ-PtAl2 and β-(Ni,Pt)Al microstructure. Full article

The demand for strategic elements, including nickel and cobalt, increases each year due to rapid technological advancements. However, due to their scarcity and environmental concerns, the development of sustainable recycling processes supported by green-energy technologies is becoming essential. In this study, a process relying on indirect bioleaching was used to recover nickel and cobalt from three different superalloy residue powders as a second source of metals, as part of a wider study to recycle superalloys within a waste process. A comparison between the three methods was carried out to analyse the bioleaching mechanisms of the target metals. Acidolysis was selected for further study due to its set-up simplicity and superior recovery rates. Variations in agitation speed of the lixiviant processing the Ni 30167 superalloy revealed that 270 rpm achieved the optimal active metal surface–oxidising agent interaction, with 60% and 70% dissolution rates after 24 h for nickel and cobalt, respectively. For the Re 30168 superalloy, extraction rates of 60% and 50% were obtained in 48 h for nickel and cobalt, respectively. The effect of hydrogen peroxide as an additive to improve metal solubilisation and overcome passivation, are discussed together with the challenges posed by the presence of iron, the materials’ elemental complexity, and its interaction with different oxidising agents. Full article

Aluminide coatings on nickel-based superalloys were synthesized via a high-temperature “clean” low-activity vapor-phase process. This process is environmentally friendly and meets manufacturers’ environmental protection requirements. Hence, it fulfils the Industry 4.0 requirements, where the reduction of environmental impact in the industrial sector is a key issue. Surface morphology, cross-section microstructure, and phase composition of the coatings were studied and compared by using an optical microscope and a scanning electron microscope (SEM) equipped with an energy dispersive spectroscope (EDS) and X-ray diffraction (XRD). Bare and coated superalloys’ lifetime was evaluated and compared via air exposure at 1100 °C. High-temperature low-activity aluminizing of the IN713, IN625, and CMSX4 superalloys enabled the obtainment of the desirable β-NiAl phase. The highest nickel content in the chemical composition of the IN713 superalloy among the investigated superalloys resulted in the highest aluminide coatings’ thickness. Moreover, the higher refractory elements concentration in the IN625 and CMSX4 superalloys than that in the IN713 superalloy may contribute to a thinner aluminide coatings’ thickness. Refractory elements diffused to the surface of the superalloy and formed carbides or intermetallic phases, which impeded outward nickel diffusion from the substrate to the surface and thereby inhibited coating growth. The obtained coatings fulfilled the requirements of ASTM B 875. Despite the fact that the coating formed on IN713 was thicker than that formed on IN625, the lifetime of both coated superalloys was comparable. Oxidation resistance of the aluminide coatings formed on the IN713 and IN625 superalloys makes them the favored choice for gas turbine applications. Full article

Laser additive manufacturing offers significant advantages for fabricating and repairing complex components. However, the complex solidification and remelting processes in nickel-based superalloys for additive manufacturing can introduce defects such as voids and cracks. Therefore, process parameters are crucial, as they significantly impact solidification and remelting, thereby affecting defect formation. In this study, laser-directed energy deposition was employed to evaluate the effects of our key process parameters on the formation of voids and cracks in a novel superalloy. The findings reveal that laser power and linear energy density significantly influence the void content and crack density. However, the influence of other process parameters on defect formation is relatively minimal. The optimal parameter space is characterized by a laser power range of 600~700 W, a linear energy density range of 60~90 J/mm and a powder feeding rate of 0.7~0.8 rpm. Moreover, the precipitation of fine MC-type carbides near the dendrites and grain-boundary misorientations within the range of 31~42° are associated with a higher propensity for crack formation. These insights provide a valuable reference for controlling the process parameters and understanding the cracking mechanisms in laser additive manufacturing of superalloys. Full article

This study investigated how long-term aging (750 °C and 950 °C) affects the microstructure and room-temperature tensile properties of the Ni-Co-Cr superalloy GH3617. Characterization (SEM, EDS, EBSD) showed that initial aging (750 °C, 500 h) formed discontinuous M₂₃C₆ carbides, pinning grain boundaries and improving strength. Prolonged aging (750 °C, 5000 h) caused M₂₃C₆ to coarsen into brittle chain-like structures (width up to 1.244 μm) and precipitated M₆C carbides, degrading grain boundaries. Aging at 950 °C accelerated this coarsening via LSW kinetics (rate constant: 6.83 × 10⁻² μm³/s), with Mo segregation promoting M₆C formation. Tensile properties resulted from competing γ′ precipitation strengthening (post-aging strength increased up to 23.3%) and grain boundary degradation (elongation dropped from 70.1% to 43.3%). Fracture shifted from purely intergranular (cracks along M₂₃C₆/γ interfaces at 750 °C) to mixed mode (cracks initiated by M₆C fragmentation at 950 °C). These insights support superalloy microstructure optimization and lifetime prediction. Full article

This study presents a bibliometric analysis of the evolution and research trends in the additive manufacturing (AM) of superalloys over the last decade (2015–2025). The review follows a structured methodology based on the PRISMA 2020 protocol, utilizing data from the Scopus and Web of Science (WoS) databases. Particular attention is devoted to the intricate process–structure–property relationships and the specific behavioral trends associated with different superalloy families, namely Ni-based, Co-based, and Fe–Ni-based systems. The findings reveal a substantial growth in scientific output, with the United States and China leading contributions and an increasing trend in international collaboration. Key research areas include process optimization, microstructural evolution and control, mechanical property assessment, and defect minimization. The study highlights the pivotal role of technologies such as laser powder bed fusion, electron beam melting, and directed energy deposition in the fabrication of high-performance components. Additionally, emerging trends point to the integration of machine learning and artificial intelligence for real-time quality monitoring and manufacturing parameter optimization. Despite these advancements, challenges such as anisotropic properties, porosity issues, and process sustainability remain critical for both industrial applications and future academic research in superalloys. Full article

This study proposes a novel unified constitutive model that systematically integrates the microstructure evolution and macroscopic stress–strain response during the hot deformation of a Ni-based superalloy. The proposed model incorporates a suite of microstructural variables, including damage fraction, recrystallization fraction, δ phase content, average grain size, and dislocation density. Furthermore, the model explicitly considers critical macroscopic stress state parameters, specifically the magnitude and orientation of maximum principal stress, hydrostatic stress component, and Mises equivalent stress. A comparative analysis of rheological curves derived from uniaxial tension and compression experiments reveals that the prediction errors of the proposed model are less than 3%. The model is subsequently implemented to investigate the evolution characteristics of the damage accumulation fraction and δ phase content under varying stress directions and initial δ phase contents. An advanced computational framework integrating the finite element method with the proposed constitutive model is established through customized subroutines. The framework exhibits exceptional predictive accuracy across critical regions of disk forging, as evidenced by a close agreement between computational and experimental results. Specifically, the relative errors for predicting recrystallization fraction and average grain size remain consistently below 8% under varying stress–strain conditions. Testing results from four representative regions demonstrate a good alignment of high-temperature tensile properties with the macroscopic stress–strain distributions and microstructure characteristics, thereby confirming the model’s reliability in simulating and optimizing the forging process. Full article

The hot deformation behavior of nickel-based superalloy 925 under different strain rates and elevated temperatures is inherently complex because of its strong dependence on strain, strain rate, and temperature. Constitutive modeling becomes essential to capture and predict this behavior accurately. In this study, two modified versions of the Kobayashi–Dodd (KD) and the Khan–Huang–Liang (KHL) models were introduced based on a detailed analysis of the alloy’s hot deformation characteristics, aiming to increase their predictive capabilities. The accuracy of the modified models, along with their original versions, was rigorously evaluated via the key statistical parameters correlation coefficient (R), average absolute relative error (AARE), and root mean square error (RMSE). The findings revealed that the modified KD and KHL models agreed well with the experimental data, indicating a remarkable fit. Both modified versions demonstrated high predictive accuracy, each achieving an R-value of 0.997. The modified KHL model reported an AARE of 3.07% and an RMSE of 7.49 MPa, whereas the modified KD model achieved an AARE of 3.19% and an RMSE of 6.64 MPa. These results confirm that the improved models offer superior performance in capturing the hot flow behavior of nickel-based superalloy 925, making them valuable tools for high-temperature forming process simulations and improving the overall performance of components. Furthermore, by enabling more efficient and optimized forming processes, these models contribute to sustainable manufacturing by minimizing material waste and optimizing energy usage, supporting global sustainability initiatives in line with SDG 9, SDG 12, and SDG 13. Full article

K417G superalloy is widely applied in gas turbine components such as blades, vanes, and nozzles. In this work, the oxidation behavior and mechanism of K417G alloy prepared by wide-gap brazing were investigated in air at 800, 900, 1000, and 1100 °C. Microstructures of the bonded joints differ in the wide-gap braze region (WGBR) and base metal (BM). The surface and cross-sectional morphology, composition, and structure of specimens were analyzed by XRD, SEM, and EDS after oxidation tests. The experimental data demonstrate that the WGBR (wide-gap brazed region) exhibits markedly superior oxidation resistance compared to the BM (base material) under elevated-temperature conditions exceeding 1000 °C. This performance disparity is quantitatively validated by oxidation kinetics analysis, where the weight gain curve of the WGBR demonstrates parabolic oxidation kinetics, as evidenced by its significantly lower parabolic rate constant relative to the BM. The oxide layers of the BM and WGBR are similar after oxidation at high temperatures of 800–900 °C, and they consist of an outermost layer of NiO, a middle mixed layer of Cr₂O₃, and an innermost layer of dendritic Al₂O₃. However, when the temperature is between 1000 and 1100 °C, the NiO on the surface of the BM spalls of due to thermal expansion coefficient mismatch in coarse-grained regions, resulting in oxidation mainly divided into outer layer Cr₂O₃ and inner layer Al₂O₃ and TiO₂. Under high-temperature oxidation conditions (1000–1100 °C), a structural transition occurs in the oxide scale of the BM, with the underlying mechanism attributable to grain-coarsening-induced oxide scale destabilization. Specifically, the coarse-grained structure of the BM (characteristic grain size exceeding 50 μm) is exhibited. Therefore, the WGBR demonstrates outstanding oxidation resistance, as evidenced by the formation of a continuous Al₂O₃ scale with parabolic rate constants of about 1.38 × 10⁻³ mg²·cm⁻⁴·min⁻¹ at 1100 °C. Full article

Aero-engine turbine vanes made from directionally solidified nickel-based superalloys often fail with crack formation from the external wall of cooling channels. Therefore, this study simulates the compressive load on the external wall of the vane and conducts a sequence of creep–fatigue evaluations at 980 °C to investigate the creep–fatigue damage mechanisms of a directionally solidified superalloy and to assess its life. It is found that at low strain ranges, creep damage is dominant, with creep cavities forming inside the specimen and fatigue sources mostly distributed in the specimen interior. As the strain range increases, the damage mechanism transitions from creep-dominated to creep–fatigue coupled damage, with cracks nucleating preferentially on the surface and exhibiting a characteristic of multiple fatigue sources. In the longitudinal (L) specimen, dislocations in multiple orientations of the {111}<110> slip system are activated simultaneously, interacting within the γ channels to form dislocation networks, and dislocations shear through the γ′ phase via antiphase boundary (APB) pairs. In the transverse (T) specimen, stacking intrinsic stacking faults (SISFs) accumulate within the limited {111}<112> slip systems, subsequently forming a dislocation slip band. The modified creep–fatigue life prediction model, incorporating strain energy dissipation and stress relaxation mechanisms, demonstrates an accurate fatigue life prediction under creep–fatigue coupling, with a prediction accuracy within an error band of 1.86 times. Full article

Directionally solidified (DS) superalloys have become a primary material choice for turbine blade applications. Due to the complex shape of the blades, certain regions inevitably experience stress axes oriented orthogonally to the crystal growth direction. Therefore, this study explores the creep characteristics of a DS superalloy in different orientations (transverse (T) versus longitudinal (L) with respect to grain growth direction) under intermediate and high temperatures (980 °C and 1070 °C), while simultaneously analyzing their respective deformation mechanisms and microstructural transformation behaviors. Experimental findings reveal pronounced orientation-dependent variations in creep performance, deformation modes, and microstructural development. Notably, the T specimen exhibits higher creep resistance at 980 °C, which can provide a basis for the design of some components that require high creep resistance and maintain small deformation. At 980 °C, L specimens primarily undergo γ′ phase shearing via antiphase boundaries (APBs) pairs, whereas T specimen exhibits APB pairs and superlattice intrinsic stacking faults (SISFs) shearing mechanisms. At 1070 °C, the L specimen exhibits dislocation shearing of γ′ alongside dislocation bypassing of tertiary γ′, while the T specimen demonstrates dislocation climbing within the γ channels. Additionally, the L specimen exhibits significant N-type rafting, while the T specimen shows significant Ostwald ripening characteristics, with an Ostwald ripening rate constant of 1.04 × 10⁻²⁰ m³/h. Full article

Nickel-based superalloys are extensively used in high-temperature applications because of their exceptional oxidation and corrosion resistance. However, their performance in aggressive environments containing molten salts, such as Na₂SO₄ and V₂O₅, remains a critical challenge. This study investigated the hot corrosion behavior of Inconel 718, Udimet 710, Nimonic 75, and Inconel 625, focusing on the role of the alloying elements in the corrosion layers and degradation mechanisms. The superalloys were exposed to 50/50 wt.% Na₂SO₄–V₂O₅ at 900 °C for 8, 48, and 96 h, and their corrosion resistance was evaluated through weight gain measurements, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). These results indicate that Mo is a key factor in accelerating degradation, with Inconel 625 exhibiting the highest weight gain owing to the formation of thermally unstable Mo-rich phases. Fe also negatively impacted the stability of the protective scale of Inconel 718, contributing to an increased corrosion rate. In contrast, Nimonic 75 exhibited the best resistance, forming more of the NiCr₂O₄ spinel phase through the reaction of Cr₂O₃ with NiO from the high Ni and Cr contents in the corrosive layers. These findings highlight the importance of alloy composition in optimizing corrosion resistance and suggest that using superalloys with lower Mo and Fe contents and higher Cr and Ni concentrations can significantly enhance the durability of superalloys in molten salt environments. Full article