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Nickel-based superalloy GH4169 has gained significant prominence in aerospace and power-generation sectors due to its exceptional resistance to fatigue, creep and corrosion at high temperatures. However, wear on the contact surface remains a concern during its operational lifespan, as it can lead to crack initiation and reduce the service life of the alloy. Therefore, this study aims to comprehensively investigate the dry-sliding wear behaviors of the GH4169 superalloy under various conditions, including temperatures, applied loads and sliding speeds via a ball-on-disc tribometer. The results obtained from the study indicate that the wear rate of the GH4169 superalloy is initially high at room temperature. However, as the temperature increases to 525 °C, the wear rate significantly decreases. Subsequently, with further temperature increase to 650 °C, there is a slight rise in the wear rate. However, the findings regarding the friction coefficient present a conflicting trend compared to the wear rate. Under the same testing conditions, the wear rate of the GH4169 superalloy at 525 °C and 650 °C demonstrates a significant reduction of 21% (0.0774 × 10–4 mm3/N.m) and 19% (0.0785 × 10–4 mm3/N.m), respectively; when compared to room temperature (0.0935 × 10–4 mm3/N.m). Besides, at room temperature, the wear track depths measure approximately 34 ± 2 µm and 55 ± 3 µm for applied loads of 20 N and 60 N, respectively. These values indicate a significant wear depth under ambient temperature conditions. On the other hand, at 525 °C, the wear track depths are slightly lower compared to those at RT. The measured depths at 525 °C amount to approximately 25 ± 2 µm and 38 ± 2 µm for applied loads of 20 N and 60 N, respectively. At high temperatures and low applied loads, the wear mechanism of the GH4169 superalloy is mainly abrasion. However, at low temperatures and high applied loads, the wear mechanism becomes more complex, involving abrasion as well as oxidation, delamination, softening and melting. This study offers valuable insights into how different wear testing parameters impact the tribological characteristics of the GH4169 superalloy. [ABSTRACT FROM AUTHOR]

Corrosion exposure study was conducted on the commercial nickel-based K411 superalloy in a simulated gas turbine operating environment (air + 2 vol% SO2) at 900 °C up to 2000 h. The corrosion behavior of the alloy was quantificationally analyzed from both morphological and chemical points with SEM, XRD, EDS, and EPMA. The results show that the formation of fine TiN inside the oxide layer can be strongly accelerated with the introduction of SO2. Sulfide is assumed as diffusion channels for gas molecules that accelerate internal nitridation. Large-volume variation caused by the TiN formation leads to a stress gradient, which induces Cr and Ni elements from inside to the surface of the alloy. The oxide scales release the compressive stresses generated by internal nitridation through forming protrusions on the surface, which is a potential risk for alloy failure. The corrosion behavior of K411 superalloy is controlled by a combination of oxidation, sulfidation, and internal nitridation whereby the relevant corrosion mechanism has been given. [ABSTRACT FROM AUTHOR]

Surface integrity—comprising abrasive embedding, work hardening, and residual stress—is crucial for the performance of nickel-based superalloy components milled by abrasive waterjet (AWJ). Effective evaluation of this integrity is therefore essential. First, the effects of pure waterjet and small-size AWJ on the milled surface were analyzed, with abrasive embedding as a key indicator. It was found that small-size AWJ significantly reduced both the number and depth of abrasive particles embedded. Next, single-factor experiments determined the influence of AWJ process parameters on abrasive embedding, leading to the identification of optimal modification schemes (modification scheme 1 and modification scheme 2) for minimizing the number and depth of abrasives. Recommended processing parameters are waterjet pressure = 100 MPa, and step-over distance = 0.38 mm. Finally, it was observed that both modification schemes decreased surface hardness while significantly increasing residual compressive stress compared to the unmodified surface. These findings offer a theoretical and practical foundation for achieving high surface integrity in the milling of nickel-based superalloys using AWJ. [ABSTRACT FROM AUTHOR]

By regulating Inconel718‐xRene88DT (x = 0–100%) alloy powder, microstructure evolution and microsegregation of as‐deposited samples fabricated by direct energy deposition (DED) are investigated. The novelty of this approach lies in the systematic regulation of the alloy composition to study its impact on microstructure and microsegregation, which is an important prerequisite to improving the performance of DED superalloys. It is found that the as‐deposited microstructure mainly consists of predominant γ columnar dendrites directionally growing along the deposition direction. With the increase of Rene88DT proportion, thelayered structure tends to be more obvious, and the amount and size of γ′ phase increases. The content of the Laves phase is in decline. As a result of the microsegregation, the needlelike δ (Ni3Nb) and lath‐shaped η (Ni3Ti) precipitate in the interdendritic regions when the proportion of Rene88DT is above 60%. The various microstructures, microsegregation, and their correlations at different proportions of Rene88DT DED samples are discussed. The relationship between composition and microstructure evolution is investigated based on the alloying mechanism, which can guide alloy design and process optimization for enhanced properties in AM‐built Ni‐based superalloys. [ABSTRACT FROM AUTHOR]

This paper focuses on the difficulties in high-quality and high-efficiency micro-milling nickel-based superalloy micro thin-walled parts. The second-generation Non-dominated Sorting Genetic Algorithm (NSGA-II) is improved. A central composite experiment is designed, and a surface roughness prediction model is developed for micro-milling thin-walled parts. A prediction model for surface residual stress on thin-walled parts is developed using an L9(34) orthogonal simulation experiment. Using the NSGA-II algorithm, the four cutting parameters (spindle speed, feed per tooth, axial cutting depth, and radial cutting depth) are optimized to achieve low surface roughness and high material removal rate, while stable cutting and surface compressive residual stress are considered constraints. Finally, the high-quality and high-efficiency micro-milling of the Inconel 718 cross-shaped thin-walled parts is realized. [ABSTRACT FROM AUTHOR]

The electrochemical machining post-processing of additively manufactured nickel-based superalloys was studied to solve the contradiction between material processing efficiency and accuracy. The research results show that the surface of the fabricated specimens presented an uneven undulating morphology due to the overlapping of the cladding tracks and the stacking of the cladding layer in the process of laser directed energy deposition. After electrochemical machining post-processing, the levelling degree of the specimen surface gradually increased with the processing. However, at the same time, the levelling efficiency of the electrochemical machining post-processing gradually decreased due to the gradual decrease of the current density difference between the peaks and valleys on the specimen surface. The current efficiency remained basically unchanged at 67.6% throughout the electrochemical machining post-processing. This study provides experimental basis and theoretical foundation for the development of new combined machining technology of nickel-based superalloys based on laser directed energy deposition and electrochemical machining. [ABSTRACT FROM AUTHOR]

Microstructure, tensile property and creep performance of a novel powder metallurgy nickel-based superalloy FGH4113A were systematically studied under two different prepared conditions. The experimental results show that the yield strengths and ultimate tensile strengths of the designed superalloy of A3-HIP and A3-HEX excess 1200 and 1650 MPa at room temperature, respectively, and still reach 900 and 1050 MPa at 800 °C. The 0.2% creep lifetime of A3-HEX is longer than that of A3-HIP. Prior particle boundaries are responsible for inferior creep property of A3-HIP. FGH4113A shows excellent tensile property, which is better than that of René104 and RR1000. The strengthening mechanism shows that superior strength of FGH4113A is attributed to precipitation strengthening. [ABSTRACT FROM AUTHOR]

The flow behavior and deformation mechanisms of the [001]-oriented single-crystal nickel-based superalloy PWA1483 are investigated under quasi-static compressive and tensile loading conditions at 750°C. We found that the tensile yield strength is larger as compared to the compressive strength, and the serrated flow only appears on the compressive stress–strain curves. Microstructural observations uncover that stacking fault shearing and microtwinning are prone to initiate in PWA1483 during tensile deformation, and the appearance of the Protevin–Le Châtelier effect in compression derives from the abrupt frequent bursts of the two mechanisms on a mesoscale, rather than the simple occurrence of these procedures. [ABSTRACT FROM AUTHOR]

The tensile behavior of single-crystal superalloys was investigated at room temperature (RT) and 850 °C, focusing on various secondary orientations. Transmission electron microscopy (TEM) and quasi in situ electron backscatter diffraction (EBSD) were employed to study the deformation mechanisms across length scales. Deformation at 850 °C enhanced the tensile ductility of the samples, evidenced by the more uniform coverage of dislocations across the γ and γ′ phases, and the fracture mode switched from pure cleavage at room temperature to mixed mode due to accelerated void growth. The influence of secondary orientations on mechanical properties is insignificant at room temperature. However, the ductility of the different secondary orientation samples shows significant variations at 850 °C, among which the one with [001] rotated 37° demonstrated superior ductility compared to others. [ABSTRACT FROM AUTHOR]

Short-time oxidation exposures of the Ni-based TROPEA single crystal superalloy was implemented to determine the nature and quantities of transient oxides in the 680–1000 °C temperature range. Experiments were carried out in situ in the SEM with reduced air pressure (150 Pa, P O 2 ~ 31.5 Pa) compared to atmospheric conditions (105 Pa, P O 2 ~ 2.1 104 Pa). TEM characterization after oxidation showed the complexity of the oxidation products developed. Aluminum underwent internal oxidation between 680 and 1000 °C. During the limited duration of oxidation, the TROPEA alloy only formed a continuous alumina layer at 1000 °C. At 680 and 850 °C, the low diffusion rate and small amount of Al in the Ni-based single crystal led to the formation of a significant amount of transient oxides such as (Ni,Co)O, compared to the desired chromia or alumina protective oxides. The lower the temperature, the smaller the size of the internal Al2O3 precipitates and the larger the transient oxide amount, which would lower the resistance of TROPEA to Type II hot corrosion. In contrast after a transient period shorter than 22 h, during which multiple transient oxide developed, the oxidation resistance would be ensured at 1000 °C by the formation of a continuous Al2O3 scale. [ABSTRACT FROM AUTHOR]

New developments in nickel-based superalloys and production methods, such as the use of additive manufacturing (AM), can result in innovative designs for turbines. It is crucial to understand how the material behaves during the AM process to advance the industrial use of these techniques. An analytical model based on reaction–diffusion formalism is developed to better explain the solidification behavior of the material during laser metal deposition (LMD). The well-known Scheil–Gulliver theory has some drawbacks, such as the assumption of equilibrium at the solid–liquid interface, which is addressed by this method. The solidified fractions under the Scheil model and the pure equilibrium model are calculated using CALPHAD simulations. A differential scanning calorimeter is used to measure the heat flow during the solid–liquid phase transformation, the result of which is further converted to solidified fractions. The analytical model is compared with all the other models for validation. [ABSTRACT FROM AUTHOR]

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Microstructure degradation and phase transformations are critical concerns in nickel-based superalloys during thermal exposure. Understanding the phase transformation mechanism requires the detailed mapping of the distribution of each phase at different degradation stages and in various precipitation sizes. However, differentiating between phases in large areas, typically on the scale of millimeters and often relying on scanning electron microscopy (SEM) techniques, has traditionally been a challenging task. In this study, we present a novel and efficient phase mapping method that leverages multiple imaging detectors and modes in SEM. This approach allows for the relatively rapid and explicit differentiation and mapping of the distribution of various phases, including MC, M23C6, γ′, and η phases, as demonstrated in a typical superalloy subjected to aging experiments at 800 °C. [ABSTRACT FROM AUTHOR]

Nickel-based superalloys have been widely used in the aerospace industry, and regulating the reinforcing phases is the key to improving the high-temperature strength of the alloy. In this study, a series of aging treatments (650 °C, 750 °C, 850 °C and 950 °C for 8 h) were designed to study different thermal deformation behaviors and microstructure evolutions for a novel nickel-based superalloy. Among the aged samples, the 950 °C aged sample achieved the peak stress of ~323 MPa during the thermal deformation and the highest microhardness of ~315 HV after thermal compression, which were the greatest differences compared to before deformation. In addition, the grains of the 950 °C sample exhibit deformed fibrous shapes, and the grain orientation is isotropic, while the other samples exhibited isotropy. In the 850 °C and 950 °C high-temperature aging samples, the γ′ precipitate (about 20 nm in size) is gradually precipitated, which inhibits the movement of dislocation in the grain during compression, thus inhibiting the occurrence of dynamic recrystallization and improving the high-temperature mechanical properties of the alloy. [ABSTRACT FROM AUTHOR]

Ni-based superalloys are widely used in aerospace applications. However, traditional constitutive equations often lack the necessary accuracy to predict their high-temperature behavior. A novel constitutive model, utilizing Taylor series expansions and partial derivatives, is proposed to predict the high-temperature flow behavior of a nickel-based superalloy. Hot compression tests were conducted at various strain rates (0.01 s−1, 0.1 s−1, 1 s−1, and 10 s−1) and temperatures (850 °C to 1200 °C) to gather comprehensive experimental data. The performance of the new model was evaluated against classical models, specifically the Arrhenius and Hensel–Spittel (HS) models, using metrics such as the correlation coefficient (R), root mean square error (RMSE), sum of squared errors (SSE), and sum of absolute errors (SAE). The key findings reveal that the new model achieves superior prediction accuracy with an R value of 0.9948 and significantly lower RMSE (22.5), SSE (16,356), and SAE (5561 MPa) compared to the Arrhenius and HS models. Additionally, the stability of the first-order partial derivative of logarithmic stress with respect to temperature ( ∂ l n σ / ∂ T ) indicates that the logarithmic stress–temperature relationship can be approximated by a linear function with minimal curvature, which is effectively described by a second-degree polynomial. Furthermore, the relationship between logarithmic stress and logarithmic strain rate ( ∂ l n σ / ∂ l n ε ˙ ) is more precisely captured using a third-degree polynomial. The accuracy of the new model provides an analytical basis for finite element simulation software. This helps better control and optimize processes, thus improving manufacturing efficiency and product quality. This study enables the optimization of high-temperature forming processes for current superalloy products, especially in aerospace engineering and materials science. It also provides a reference for future research on constitutive models and high-temperature material behavior in various industrial applications. [ABSTRACT FROM AUTHOR]

An Inconel 740H nickel-based alloy was fabricated via wire arc additive manufacturing. The as-welded and heat-treated samples were analyzed to investigate their phase composition, microstructure, crystal structure, and mechanical properties. After heat treatment, the sample exhibited a columnar crystal zone microstructure consisting of a γ matrix + precipitated phase, the remelting zone metallographic structure was a γ matrix + precipitated phase, and the HAZ metallographic structure was a γ matrix + precipitated phase. Transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) were used to show that the welded sample exhibited many dislocations, a few inclusions, and carbides, nitrides, and γ' precipitates in its crystal structure. In contrast, the crystal structure of the heat-treated sample exhibited a lower number of dislocations and significantly higher carbide and γ' precipitate content. Moreover, the mechanical performance of these samples was excellent. This heat-treatment process improved the sample strength by about 200 MPa, leading to better high-temperature mechanical properties. This work is anticipated to offer theoretical and experimental support for using additive manufacturing methods in the manufacturing of nickel-based superalloy components. [ABSTRACT FROM AUTHOR]

Shrinkage porosity is a common issue in nickel-based superalloy 718 turbine blade investment castings, potentially compromising the mechanical properties of the final component. This study utilized finite element simulation to explore the impact of mold dwell time preceding the melt pouring process on the filling, solidification, and shrinkage defects in Inconel 718 superalloy turbine blade investment casting. The simulation results indicate that as the mold dwell time increases from 0 to 420 s, the shell temperature decreases from 1000 to 860 °C, while the total shrinkage volume and frequency rise from 2.6154 to 2.9398 cm3. This phenomenon mainly arises from the decrease in shell temperature and the evolution of solid fraction within the superalloy casting. For mold dwell times of 180 s, 300 s, and 420 s, the shell temperature directly declines to 900–950 °C, 850–940 °C, and 830–890 °C, respectively, before ascending to around 1200 °C during melt pouring. Subsequently, the microstructure of both as-cast and heat-treated superalloy 718 castings underwent observation and comparison. [ABSTRACT FROM AUTHOR]

The creep behaviors of a novel polycrystalline nickel-based superalloy are investigated at a wide applied stress range of 500-950 MPa and temperature ranging from 650 to 750 °C. And the microstructure and deformation mechanisms are also analyzed. The results indicate that all creep curves of the novel nickel-based superalloy are mainly consist of the primary and accelerated stages, whereas the steady-state stage is not obviously observed. The minimum creep rate increases and the corresponding creep life decreases with the applied stress increasing at constant temperature. The relative longer creep life at 650 °C could be attributed to the coupling of stacking faults in the interior of γ' and deformation twinning. [ABSTRACT FROM AUTHOR]

This paper develops a thermodynamic entropy-based life prediction model to estimate the low-cycle fatigue (LCF) life of the nickel-based superalloy GH4169 at elevated temperature (650 °C). The gauge section of the specimen was chosen as the thermodynamic system for modeling entropy generation within the framework of the Chaboche viscoplasticity constitutive theory. Furthermore, an explicitly numerical integration algorithm was compiled to calculate the cyclic stress–strain responses and thermodynamic entropy generation for establishing the framework for fatigue life assessment. A thermodynamic entropy-based life prediction model is proposed with a damage parameter based on entropy generation considering the influence of loading ratio. Fatigue lives for GH4169 at 650 °C under various loading conditions were estimated utilizing the proposed model, and the results showed good consistency with the experimental results. Finally, compared to the existing classical models, such as Manson–Coffin, Ostergren, Walker strain, and SWT, the thermodynamic entropy-based life prediction model provided significantly better life prediction results. [ABSTRACT FROM AUTHOR]

Unified Mechanics Theory’s (UMT) entropy-based damage parameter, also known as the “Thermodynamic State Index” has been proven to be consistent and useful in predicting the fatigue life of different metal alloys. In recent times, studies have also demonstrated its applicability towards creep damage in nickel-basedsuperalloys under a limited set of conditions. However, the usefulness of the “Thermodynamic State Index” in estimating damage at different temperatures, and creep loads for different metal alloys has not been evaluated yet. In this paper, creep in INCONEL 600 alloy is modeled using Norton’s creep law modified with entropy-based damage (Thermodynamic State Index). The model is calibrated to predict both damage and creep strains for any given input of stress, temperature, and time. The available database on INCONEL 600 is used in parts to both calibrate and validate the prescribed model. The damage evolution for different cases is compared and imminent conclusions are drawn. [ABSTRACT FROM AUTHOR]

Casting failures are caused by the thermal stress and hydraulic pressure of the molten metal during the investment casting process due to the insufficient high-temperature strength of the ceramic shell. This work investigated how the high-temperature flexural strength of aluminosilicate ceramic shells varies with temperature, different types of back-up sands, manufacturing processes, and the thickness of back-up coats by a three-point bending test. The results showed that flexural strength at room temperature is half of the high-temperature flexural strength at 1000 °C, almost equal to that at 1200 °C, and about three to eight times higher than that at 1400 °C. In comparison with the fused silica, aluminosilicate shells have inadequate high-temperature flexural strength at 1400 °C, regardless of mullite and bauxite as back-up sands. In addition, the mullite shell prepared by the automated robotic arm has higher flexural strength than one made through the manual operation process. Finally, the high-temperature flexural strength of the bauxite shell is unaffected by the increasing thickness of back-up coats. This study provides a guide to improve the high-temperature flexural strength of aluminosilicate shells and a theoretical foundation for reducing defects in castings. [ABSTRACT FROM AUTHOR]

The microstructures and mechanical properties of a γ′-strengthened nickel-based superalloy, GH4099, produced by laser powder bed fusion, at room temperature and 900 °C are investigated, followed by three various heat treatments. The as-built (AB) alloy consists of cellular/dendrite substructures within columnar grains aligning in <100> crystal orientation. No γ′ phase is observed in the AB sample due to the relatively low content of Al +Ti. Following the standard solid solution treatment, the molten pool boundaries and cellular/dendrite substructures disappear, whilst the columnar grains remain. The transformation of columnar grains to equiaxed grains occurs through the primary solid solution treatment due to the recovery and recrystallization process. After aging at 850 °C for 480 min, the carbides in the three samples distributed at grain boundaries and within grains and the spherical γ′ phase whose size is about 43 nm ± 16 nm develop in the standard solid solution + aging and primary solid solution + aging samples (SA and PA samples) while the bimodal size of cubic (181 nm ± 85 nm) and spherical (43 nm ± 16 nm) γ′ precipitates is presented in the primary solid solution + secondary solid solution + aging sample (PSA samples). The uniaxial tensile tests are carried out at room temperature (RT) and 900 °C. The AB sample has the best RT ductility (~51% of elongation and ~67% of area reduction). Following the three heat treatments, the samples all acquire excellent RT tensile properties (>750 MPa of yield strengths and >32% of elongations). However, clear ductility dips and intergranular fracture modes occur during the 900 °C tensile tests, which could be related to carbide distribution and a change in the deformation mechanism. [ABSTRACT FROM AUTHOR]

Engine components, particularly exhaust valves, are manufactured by a specific forming process known as electric upsetting, which contributes to microstructures with finer grains which enhance the performance of these components. To this end, it is necessarily required to describe the grain evolution behaviors of heat-resistant alloys during the electrical-thermal-mechanical coupling forming process. The grain evolution behaviors of Ni80A superalloy including dynamic recrystallization (DRX) kinetics models and mesoscale cellular automaton (CA) model are solved from the acquired stress–strain curves in resistance heating isothermal compression tests. Following which, a multi-field and multi-scale coupling FEM model is established by embedding the multi-scale grain evolution models into the electrical-thermal-mechanical multi-field coupling compression model. Then the grain evolution behaviors in isothermal compressions with processing conditions are reproduced by simulations. The results reveal that during the isothermal compressions, recrystallized grains intend to bulge and generate around the original grain boundaries, representing as 'necklace' microstructures inhomogeneously distributed in the matrix, and then such grain morphology is gradually replaced by refined and equiaxed DRX grains. For a fixed strain, grain size decreases with decreasing temperature and increasing strain rate. Finally, the EBSD characterization results show that the developed FEM model can well describe the grain evolution behaviors of Ni80A superalloy in electrical-thermal-mechanical coupling compression process. [ABSTRACT FROM AUTHOR]

The tribological properties of γ-TiAl alloys under sliding condition have been well established, but the mechanisms for fretting wear, especially at elevated temperature, remain to be further clarified. In the present study, the tribological behaviors and mechanisms of a γ-TiAl alloy were investigated under an elevated temperature fretting condition. The wear scars, debris, and tribolayers were studied with scanning electron microscope, energy dispersive spectrometer, and Raman spectrometer. The structural and mechanical properties of the tribolayers were investigated utilizing transmission electron microscope and nanoindentation tests. The results demonstrated that the severe adhesive wear, delamination, and abrasive wear in the early stage of fretting resulted in high wear rate of the γ-TiAl alloy. As fretting progresses, the formation of tribolayers with nanograins and excellent mechanical properties improved the fretting wear resistance of the γ-TiAl alloy. Due to the protective effect of the adhesively transferred γ-TiAl, the wear rate of the nickel-based superalloy counterpart was significantly lower. [ABSTRACT FROM AUTHOR]

Vacuum electron-beam welding (EBW) was used to join the precipitation-strengthened GH4169 superalloy and a new nickel-based superalloy IC10 to fabricate the turbine blade discs. In this study, a solid solution (1050 °C/2 h for GH4169 and 1150 °C/2 h for IC10) and different heat-exposure temperatures (650 °C, 750 °C, 950 °C and 1050 °C/200 h, respectively) were used to study the high-temperature tensile properties and microstructure evolution of welded joints; meanwhile, the formation and evolution of the second phases of the joints were analyzed. After EBW, the welded joint exhibited a typical nail morphology, and the fusion zone (FZ) consisted of columnar and cellular structures. During the solidification process of the molten pool, Mo elements are enriched in the dendrites and inter-dendrites, and that of Nb and Ti elements was enriched in the dendrites, which lead to forming a non-uniform distribution of Laves eutectic and MC carbides in the FZ. The microhardness of the FZ gradually increased during thermal exposure at 650 °C and reached 300–320 HV, and the γ′ and γ″ phases were gradually precipitated with size of about 50 nm. Meanwhile, the microhardness of the FZ decreased to 260–280 HV at 750 °C, and the higher temperature resulted in the coarsening of the γ″ phase (with a final size of about 100 nm) and the formation of the acicular δ-phase. At 950 °C and 1050 °C, the microhardness of FZ decreased sharply, reaching up to 170~190 HV and 160~180 HV, respectively. Moreover, the Laves eutectic and MC carbides are dissolved to a greater extent without the formation of γ″ and δ phases; as a result, the absent of γ″ and δ phases are attributed to the significant improvement of segregation at higher temperatures. [ABSTRACT FROM AUTHOR]

Trace elements such as boron (B) and zirconium (Zr) can increase creep resistance in nickel-based superalloys. This study investigates the change of microstructures on the grain boundary (GB) in phase-controlled nickel-based superalloys through the addition of trace elements. The basis alloy without B and Zr has distributed micrometer-sized (Nb, Ti)C and Cr23C6 carbides at the GBs. Zr is detected alongside Nb and Ti within certain (Nb, Ti)C carbides and its addition increases the fraction of (Nb, Ti)C or (Nb, Ti, Zr)C carbides. B affects the formation of precipitates constructed by nanometer-sized precipitates, which are Cr23C6 carbides, Cr23(C, B)6 boro-carbides, and Cr-rich borides, surrounded by γ' phases. This film structure, which includes nanometer-sized precipitates surrounded by γ' phases, forms more continuously with the addition of B and Zr. It is constructed with precipitates of (Nb, Ti)C carbides and Cr23(C, B)6 boro-carbides surrounded by γ' phases. Numerous nanometer-sized precipitates (i.e., (Nb, Ti)C and Cr23(C, B)6) are distributed alternately within the film structure. The effect of the addition of B and Zr is such that nucleation sites of each precipitate are formed simultaneously and alternately along the GBs. The experimental results were discussed by correlating them with the predicted fraction of stable phases depending on the temperatures of these alloys, using the JMatPro program. [ABSTRACT FROM AUTHOR]

Accurate determination of thermo‐mechanical properties in precipitation hardenable materials using an electro‐thermal mechanical testing (ETMT) system is a well‐established challenge. The non‐uniform distribution of temperature resulting from heating based on the joule effect (i.e., resistivity heating) leads to heterogeneous deformation along the gauge length, owing to the temperature dependency of mechanical properties, which makes their direct measurements complicated. This study presents an evaluation of four different miniaturised sample geometries that were tested to achieve an optimised sample with acceptable uniform strain and temperature distributions in the gauge volume. In‐situ displacement mapping, using digital image correlation (DIC), was utilised to calibrate the optimised sample dimensions with the aim of forcing the deformation to the hottest region of the gauge lengths during the tests. Tests were carried out on Inconel 718 (IN718) at 720°C, an optimal temperature for the precipitation of γ″, the primary strengthening particle in this alloy. The results showed that only in the case of the geometry proposed in this study (i.e., a sample with a short gauge length [~2 mm]) did the deformation acceptably localise at the centre, compared to other geometries. A correction methodology is developed that equates the strain measured using DIC over the 2 mm gauge length of the modified sample geometry with the strain measured using the linear variable differential transformer (LVDT) integrated to the ETMT, making future tests on IN718, and other precipitation hardenable materials, possible without the need for the use of a DIC system. [ABSTRACT FROM AUTHOR]

This study applied plasma transferred arc (PTA) welding to fabricate hard cladding layers by using nickel-based superalloy (NCR7) and niobium carbide (NbC) powders as filler material. The resultant composite claddings were coated onto ductile iron and then analyzed to understand the effect of different quantities of NbC on the solidification structures of the cladding layers and on the characteristics of the interface between the cladding layers and the ductile iron. Cutting tests were also conducted to assess the morphology and mechanism of flank wear on PTA NbC/NCR7 composite cladding tools. The results revealed that the cladding specimens' microstructures comprised a mixture of dendrites and interdendritic eutectics along with a considerable quantity of carbides (MC, M7C3, and M23C6) scattered within the γ-Ni matrix. Incorporating considerable NbC carbide enhanced the claddings' surface hardness, but it had a limited effect on improving the flank wear on the turning tools. The flank wear on the composite cladding tools intensified as the NbC content was increased. The wear behavior, defined by brittle fractures and stripped NbC particles, led to a decline in turning tool performance. Accordingly, the Ni-based alloy composite cladding with larger NbC particles appears more suitable for sliding or erosion applications under normal stress conditions. [ABSTRACT FROM AUTHOR]

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

Inclusions are important phases affecting material properties in complicated ways. In this paper, a quantitative study of the addition of HfO2 inclusions to DZ125 nickel-based superalloys was performed. Experimental results showed that the introduction of HfO2 inclusions caused a loss of strength and ductility. The carbide morphology also changed significantly from skeletal-shaped to block-shaped, resulting in a remarkable discrepancy in the fracture behavior under quasi-in-situ tensile testing. The SEM dynamic observations showed that cracks were initiated from the skeletal carbides and almost failed to propagate into the matrix. In contrast, the damage behavior of block-shaped carbides also involved internal cracking but with a tendency to form interconnected microcracks during propagation. A crystal plasticity finite element model (CPFEM) method was further developed to study the stress/strain behavior during the deformation process, considering the crystal orientations and microstructure morphologies from the EBSD data. Those elastoplastic parameters were determined through nanoindentation experiments. Simulation results verified that blocky carbides produced a pronounced strain concentration at the interface of the carbides and matrix, thereby increasing the tendency of crack formation. This paper provides a fundamental understanding of the role of inclusions in material recycling applications. [ABSTRACT FROM AUTHOR]

In order to repair a failed AlSiY coating on aeroengine turbine components, the AlSiY coating was stripped using a nitric acid-based removal reagent. The homogeneity of chemical stripping was evaluated and the stripping mechanism was clarified using first-principles calculations. The effects of hydrofluoric acid (HF) and chromium trioxide (CrO3) on the homogeneity of chemical stripping were investigated by calculating the electronic work functions (EWFs) of the stripped surfaces. The results showed that the stripped surfaces of the AlSiY coating exhibited a serrated appearance when it was etched by a single nitric acid solution, indicating severely inhomogeneous stripping. With the addition of HF and/or CrO3, the homogeneity of chemical stripping could be greatly improved, which was attributed to the increased EWF of the (200) surface and the decreased EWF of the (110) surface, causing the corrosion cathode to transition from the (110) surface to the (200) surface. The HF+CrO3+HNO3 mixed reagent was the optimal combination for the uniform stripping of the AlSiY coating, while the inner layer was not broken. The Al atoms on the surface could be preferentially removed due to the strong bonding with acid ions. The research method proposed in the present work will provide a new means to design chemical removal reagents. [ABSTRACT FROM AUTHOR]

We investigate the tensile deformation behavior and mechanism of nickel-based superalloy CM247LC, which has been subjected to various ageing treatment schemes, but possesses almost the same γ′ particle size, at 600°C. It is found that the transition in the deformation mode from particle shearing plus microtwinning to particle shearing accounts for the decrease in the work-hardening rate and tensile strength with ageing temperature. Our study provides a new strategy to design the heat treatment schedule to achieve a good compromise between the strength and plasticity for superalloys by tunning the operative deformation and fracture mechanisms. The work provides new insights into understanding the influence of ageing heat treatment or microstructural features on the mechanical properties and corresponding deformation and fracture mechanisms of precipitate-hardened superalloys. [ABSTRACT FROM AUTHOR]

The turbine section of turbojet engines operates above 900 °C. The cast Ni-based superalloy blades and vanes are used in this section. These components which are working in a very aggressive environment are usually applied with diffusion coatings. These coatings are used to increase oxidation resistance of parts and have evolved from plain aluminide coating to platinum-doped coating. Although the positive effect of platinum–aluminide coatings on the oxidation resistance of the superalloys is reported in several studies, the influence of this type of coatings on the mechanical properties of superalloys is somewhat challenging. This tutorial review of Pt–Al coatings covers: how they supply protection against cyclic oxidation, how they are employed, their microstructure characterization, and their influence on the mechanical behavior of Ni-based superalloys. The present review tries to collect all the available information on the subject and seeks the optimum correlation between Pt–Al coating characterization and mechanical/cyclic oxidation behavior of the coated superalloys. [ABSTRACT FROM AUTHOR]

Nickel-based superalloy Inconel 718 is widely used in the aerospace industry for its excellent high-temperature strength and thermal stability. However, milling Inconel 718 presents challenges because of the significantly increased cutting force and vibration, since Inconel 718 is a typical difficult-to-machine material. This paper takes the milling process of Inconel 718 as the research object, initially, and a milling force model of Inconel 718 is established. Subsequently, the finite element analysis method is used to analyze the stress field, temperature field, and milling force in the milling process of Inconel 718. Building upon this, a dynamic equation of the milling of Inconel 718 is established, and based on the modal experiment, stability lobe diagrams are drawn. Furthermore, milling experiments on Inconel 718 are designed, and the results calculated using the milling force model and finite element analysis are verified through comparison to the experimental results; then, the fmincon optimization algorithm is used to optimize the processing parameters of Inconel 718. Eventually, the results of the multi-objective optimization illustrate that the best processing parameters are a spindle speed of 3199.2 rpm and a feed speed of 80 mm/min with an axial depth of cut of 0.25 mm. Based on this, the best machining parameters are determined, which point towards an improvement of the machining efficiency and quality of Inconel 718. [ABSTRACT FROM AUTHOR]

K439B nickel-based superalloy is a new type of high-temperature material. There is insufficient research on its constitutive equations and numerical modeling of thermal stress. Isothermal tensile experiments of K439B superalloy at different temperatures (20 °C-1,000 °C) and strain rates (1.33×10-3 s-1-5.33×10-3 s-1) were performed by using a Gleeble-3800 simulator. The elastic moduli at different temperatures (20 °C-650 °C) were measured by resonance method. Subsequently, stress-strain curves were measured for K439B superalloy under different conditions. The elastic-viscoplastic constitutive equations were established and the correspongding parameters were solved by employing the Perzyna model. The verification results indicate that the calculated values of the constitutive equations are in good agreement with the experimental values. On this basis, the influence of process parameters on thermal stress was investigated by numerical simulation and orthogonal experimental design. The results of orthogonal experimental design reveal that the cooling mode of casting has a significant influence on the thermal stress, while pouring temperature and preheating temperature of shell mold have minimal impact. The distribution of physical fields under optimal process parameters, determined based on the orthogonal experimental design results, was simulated. The simulation results determine separately the specific positions with maximum values for effective stress, plastic strain, and displacement within the casting. The maximum stress is about 1,000.0 MPa, the plastic strain is about 0.135, and the displacement is about 1.47 mm. Moreover, the distribution states of thermal stress, strain, and displacement are closely related to the distribution of the temperature gradient and cooling rate in the casting. The research would provide a theoretical reference for exploring the stress-strain behavior and numerical modeling of the effective stress of the alloy during the casting process. [ABSTRACT FROM AUTHOR]

The effect of C content on the microstructure and stress rupture properties of nickel-based superalloy K4750 was studied by SEM, EBSD, TEM, EPMA and stress rupture tests. With the increase in C content, the size and quantity of MC and M23C6 carbides in experimental alloys increased, and the morphology of MC carbides changed from small blocky or rod to large blocky or skeleton. The inhibition of MC carbides on grain boundary migration made the grain size of as-cast alloys inversely proportional to C content. As C content went from 0.07 to 0.10 wt.% and then to 0.12 wt.%, the stress rupture life of K4750 alloy at 750 °C/430 MPa increased from 160.7 to 222.0 h, and then decreased to 184.4 h, and the elongation increased from 5.1 to 11.5% and then decreased to 9.8%. The difference of stress rupture properties of K4750 alloys could be attributed to the influence of varied C content on carbides precipitation characteristics. The moderate increase in MC and M23C6 carbides could effectively pin grain boundaries and reduced the tendency of forming micro-voids and micro-cracks, which was beneficial to stress properties of K4750 alloy. On the contrary, when the size and quantity of carbides increased excessively, they could become potential crack sources in the process of stress rupture tests. [ABSTRACT FROM AUTHOR]

The structure and properties of samples obtained by the laser powder bed fusion (LPBF) method from the AZhK alloy, intended for the manufacture of heavily loaded body parts with operating temperatures up to 800 °C, have been studied. The optimal mode of LPBF, ensuring the attainment of the minimal residual porosity of 0.02%, was identified for the superalloy AZhK. Additionally, the evolution of the microstructure of LPBF samples after hot isostatic pressing (HIP) and heat treatment (HT) was studied using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The macrostructure of LPBF samples is represented by columnar grains oriented in the direction of predominant heat dissipation, perpendicular to the build plate. At the microlevel, the structure consists of colonies of columnar dendrites. Nb4AlC3 and Nb6C4 carbides, as well as the Mo2Hf Laves phase, are precipitated in the interdendritic region as a result of doping element segregation. The low strength of the LPBF samples (σ = 967 ± 10 MPa) is caused by the fact that there are no reinforcing particles and by high internal stress due to high crystallization speed. HIP and HT were found to have a favorable effect on the structure and properties of the LPBF samples. The post-treatment resulted in uniform distribution of γ′-phase precipitates sized up to 250 nm in the matrix bulk and carbides at grain boundaries, as well as Laves phase dissolution. Therefore, the strength characteristics were significantly improved: by 45% at room temperature and by 50% at elevated temperatures. High strength and ductility were attained (at 20 °C, σ20 = 1396 ± 22 MPa and δ = 19.0 ± 3.0 %; at 650 °C, σ650 = 1240 ± 25 MPa and δ = 15.8 ± 1.5%; at 750 °C, σ750 = 1085 ± 23 MPa and δ = 9.1 ± 2.3%). An ejector-type part was fabricated, and its geometric parameters coincided with those in the electronic models. After conducting computed tomography, it was found that there are no defects in the form of non-fusion and microcracks within the volume of the part; however, it was observed that the pore size is ≥20 μm. [ABSTRACT FROM AUTHOR]

In this work, IN738 superalloy used previously in gas turbines was recycled and used as a working electrode for the electrooxidation of different fuels, namely ethylene glycol, ethanol, and urea. The electrocatalytic efficiency of the electrode was studied by cyclic voltammetry, chronoamperometry, and electrochemical impedance. Several kinetics parameters like diffusion coefficient, Tafel slope, rate constant, and activation energy were calculated. The modified electrode was characterized as received using XRD, SEM, and EDAX to elucidate the crystal structure and surface morphology before and after electrochemical oxidation. The anodic current densities of electrochemical oxidation of ethanol, ethylene glycol, and urea were 29, 17, and 12 mA.cm−2, respectively, in an alkaline solution at a potential of 0.6 V (vs. Ag/AgCl). The kinetic parameters like diffusion coefficients for ethanol, ethylene glycol, and urea were found to be 1.5 × 10–6, 1.038 × 10–6, and 0.64 × 10–6 cm2 s−1, respectively. The charge transfer resistances were estimated for electrooxidation of different fuels by electrochemical impedance spectroscopy (EIS). [ABSTRACT FROM AUTHOR]

The nucleation and the growth of misoriented micro-structure components in single crystals depend on various process parameters and alloy compositions. Therefore, in this study, the influence of different cooling rates on carbon-free, as well as carbon-containing, nickel-based superalloys was investigated. Castings were carried out using the Bridgman and Bridgman–Stockbarger techniques under industrial and laboratory conditions, respectively, to analyze the impact of temperature gradients and withdrawing rates on six alloy compositions. Here, it was confirmed that eutectics could assume a random crystallographic orientation due to homogeneous nucleation in the residual melt. In carbon-containing alloys, eutectics also nucleated at low surface-to-volume ratio carbides due to the accumulation of eutectic-forming elements around the carbide. This mechanism occurred in alloys with high carbon contents and at low cooling rates. Furthermore, micro-stray grains were formed by the closure of residual melt in Chinese-script-shaped carbides. If the carbide structure was open in the growth direction, they could expand into the interdendritic region. Eutectics additionally nucleated on these micro-stray grains and consequently had a different crystallographic orientation compared with the single crystal. In conclusion, this study revealed the process parameters that induced the formation of misoriented micro-structures, which prevented the formation of these solidification defects by optimizing the cooling rate and the alloy composition. [ABSTRACT FROM AUTHOR]

The yield strength of the [001]-orientated single-crystal nickel-based superalloy PWA1483 is investigated under tension/compression at 1000 and 1100 °C. We found that the compressive yield strength is larger than the tensile strength. Microstructural observations disclose that the dominant deformation modes are stacking fault shearing and microtwinning in compression at 1000 °C, whereas dislocation climb controls the plastic deformation under the other three deformation conditions, although the above two processes also occur. Based on these results, it is deemed that the frequent occurrence of <112>{111} slip accounts for the tension/compression asymmetry in the yield strength of PWA1483 at high temperatures. The tension/compression asymmetry concerning the yield strength, stacking fault shearing and mcirotwinning at 1000 and 1100 °C in the [001]-oriented single-crystal nickel-based superalloy is uncovered for the first time. [ABSTRACT FROM AUTHOR]

Primary dendrite arm spacing (PDAS) is a crucial microstructural feature in nickel-based superalloys produced by laser cladding. In order to investigate the effects of process parameters on PDAS, a multi-scale model that integrates a 3D transient heat and mass transfer model with a quantitative phase-field model was proposed to simulate the dendritic growth behavior in the molten pool for laser cladding Inconel 718. The values of temperature gradient (G) and solidification rate (R) at the S/L interface of the molten pool under different process conditions were obtained by multi-scale simulation and used as input for the quantitative phase field model. The influence of process parameters on microstructure morphology in the deposition layer was analyzed. The result shows that the dendrite morphology is in good agreement with the experimental result under varying laser power (P) and scanning velocity (V). PDAS was found to be more sensitive to changes in laser scanning velocity, and as the scanning velocity decreased from 12 mm/s to 4 mm/s, the PDAS increased by 197% when the laser power was 1500 W. Furthermore, smaller PDAS can be achieved by combining higher scanning velocity with lower laser power. [ABSTRACT FROM AUTHOR]

This study investigated the effect of building direction (BD) and three-step heat treatment on the microstructure and mechanical properties of a nickel-based superalloy Inconel 939 produced by additive manufacturing (AM), and it revealed the differences to the conventional cast superalloy. Tensile specimens were printed in horizontal and vertical BDs, and tensile tests were performed at room temperature, 700 °C and 800 °C. Thorough microstructural scrutiny conducted through light and electron microscopy revealed microstructural differences between AM and cast Inconel 939. The columnar grain structure with a preferential orientation of <001> was typical for AM alloy, whereas polyhedral grain without any specific orientation was typical for cast alloy. Experiments showed that the AM material had much better mechanical properties than the cast material. Heat treatment resulted in a formation of a fine dispersion of spherical γ′ nanoprecipitates, triggering a considerable increase in tensile strength and a drop in ductility. [ABSTRACT FROM AUTHOR]

During the multi-laser powder bed fusion (ML-PBF) process, the quality of the overlap region is essential to ensure the integrity between different laser scanning areas. Here, six different overlap region widths (ORWs) are selected to systematically investigate the effect of ORWs on densification, metallurgical defects, crystalline microstructure, and mechanical performance of the Hastelloy X samples processed by multi-laser powder bed fusion. ORWs are set to 0, 50, 100, 150, 200, and 250 μm, respectively. With an increment in ORW, the porosity gradually increases from 0.01% to 7.08%. Inversely, microcracks are reduced with increasing the ORWs due to the smaller width-to-depth ratio of the melt pools and the increased degree of recrystallisation. All the samples display equivalent ultimate tensile strength of ~880 MPa, while the elongations at break of the overlap samples are 3.5%-10.5% lower than that of the single-laser processed one (28.4%). The inferior ductility is ascribed to the decreased densification in the overlap regions, of which the adverse effect can be minimised when an ORW of 150 μm is utilised. This work is anticipated to provide efficient reference and theoretical guidance for the large-size nickelbased superalloy components fabricated by ML-PBF. [ABSTRACT FROM AUTHOR]

Electrically assisted (EA) forming is a plastic forming technique under the coupling action of multiple energy fields, such as force field, temperature field, and electric field. It is suitable for the forming of difficult-to-deform materials such as nickel-based superalloys. In this paper, uniaxial tensile tests on nickel-based superalloy sheets were carried out using the pulsed current assisted with different parameters. The experimental results show that the flow stress of the material decreased with the increase in the current density under a high-frequency pulsed current, and the Joule heating effect explains the flow stress drop. In the pulsed current application process, the different types of Portevin–Le Chatelier phenomena appeared with the increase in the current density. The decrease in elongation assisted by the pulsed current was explained by analyzing the inhomogeneity of the maximum Joule heating temperature distribution. In addition, the digital image correlation (DIC) analysis was used to analyze the local strain behavior of the pulsed current-assisted tensile process. Under the application of a high-frequency pulse current, the specimen exerted an inhomogeneous temperature increase and local hot pressing stress, which resulted in the inhomogeneous distribution of the local strain. [ABSTRACT FROM AUTHOR]

SiAlON is one of the problematic and least previously studied but prospective cutting ceramics suitable for most responsible machining tasks, such as cutting sophisticated shapes of aircraft gas turbine engine parts made of chrome–nickel alloys (Inconel 718 type) with increased mechanical and thermal loads (semi-finishing). Industrially produced SiAlON cutting inserts are replete with numerous defects (stress concentrators). When external loads are applied, the wear pattern is difficult to predict. The destruction of the cutting edge, such as the tearing out of entire conglomerates, can occur at any time. The complex approach of additional diamond grinding, lapping, and polishing combined with an advanced double-layer (CrAlSi)N/DLC coating was proposed here for the first time to minimize it. The criterion of failure was chosen to be 0.4 mm. The developed tri-nitride coating sub-layer plays a role of improving the main DLC coating adhesion. The microhardness of the DLC coating was 28 ± 2 GPa, and the average coefficient of friction during high-temperature heating (up to 800 °C) was ~0.4. The average durability of the insert after additional diamond grinding, lapping, polishing, and coating was 12.5 min. That is superior to industrial cutting inserts and those subjected to (CrAlSi)N/DLC coating by 1.8 and 1.25 times, respectively. [ABSTRACT FROM AUTHOR]

In the context of the use of AM, particularly in the L-PBF technique, the printability characterization of material occurs through the identification of its printability map as a function of printing process parameters. The printability map identifies the region where the powder melting is optimal and ensures a dense and defect-free material. Identifying the zones affected by physical phenomena that occur during the printing process which lead to material defects such as keyhole, lack of fusion and balling mode is also possible. Classical methods for the characterization of material and the identification of its printability map require the printing of a large number of specimens. The analysis of the specimens is currently time-consuming and costly. This paper proposed a methodology to identify optimal process parameters in L-PBF using an integrated single and multi-tracks analyses embedded in an overall algorithm with detailed metrics and specific factors. The main scope is to speed up the identification of printability window and, consequently, material characterization, reducing the number of micrographic analyses. The method is validated through an experimental campaign assessing the material microstructure in terms of porosity and melt pool evaluation. The case study on IN718 superalloy shows how the application of the proposed method allows an important reduction of micrographic analysis. The results obtained in the case study are a reduction of 25% for the complete definition of the printability map and more than 90% for identifying the zone with a high productivity rate. [ABSTRACT FROM AUTHOR]

This study quantified the semi-solid constitutive behavior of GH4710 superalloy using a Gleeble thermo-mechanical physical simulation system. The stress–strain curves, thermal analysis curves and microstructure indicate that the GH4710 superalloy undergoes a mechanical behavioral transition from ductile to brittle to ductile during solidification. In the brittle temperature range, solid-phase creep is the only mechanism that can accommodate solidification shrinkage and thermal stresses, and the dispersion or diffusion of γ/γ′ eutectic liquid films along grain boundaries enhances the alloy’s hot tearing tendency. At this stage, the intergranular strain is transmitted through the liquid film, which converts to intergranular bridging. This process reaches a critical state as the intergranular strain reaches a critical state when the liquid film ruptures, forming a hot tearing nucleus and leading to the further development of thermal cracking. Based on the analysis of microstructural evolution and hot tearing mechanism, we introduce a new independent variable, i.e., the fraction of grain boundary area covered with liquid. The fraction of grain boundary area covered with liquid was calculated by geometrical modeling, and the value rises sharply with the increase of liquid fraction, which reflects the effective contact area of GH4710 superalloy dendrites at the end of solidification. The main novelty of the proposed constitutive model is that it is capable of continuously simulating the stress–strain evolution of GH4710 superalloy ingot throughout the cooling process from the mushy zone to room temperature, and all the necessary input data can be obtained from conventional microstructure analysis and tensile tests.Graphical Abstract: This study quantified the semi-solid constitutive behavior of GH4710 superalloy using a Gleeble thermo-mechanical physical simulation system. The stress–strain curves, thermal analysis curves and microstructure indicate that the GH4710 superalloy undergoes a mechanical behavioral transition from ductile to brittle to ductile during solidification. In the brittle temperature range, solid-phase creep is the only mechanism that can accommodate solidification shrinkage and thermal stresses, and the dispersion or diffusion of γ/γ′ eutectic liquid films along grain boundaries enhances the alloy’s hot tearing tendency. At this stage, the intergranular strain is transmitted through the liquid film, which converts to intergranular bridging. This process reaches a critical state as the intergranular strain reaches a critical state when the liquid film ruptures, forming a hot tearing nucleus and leading to the further development of thermal cracking. Based on the analysis of microstructural evolution and hot tearing mechanism, we introduce a new independent variable, i.e., the fraction of grain boundary area covered with liquid. The fraction of grain boundary area covered with liquid was calculated by geometrical modeling, and the value rises sharply with the increase of liquid fraction, which reflects the effective contact area of GH4710 superalloy dendrites at the end of solidification. The main novelty of the proposed constitutive model is that it is capable of continuously simulating the stress–strain evolution of GH4710 superalloy ingot throughout the cooling process from the mushy zone to room temperature, and all the necessary input data can be obtained from conventional microstructure analysis and tensile tests. [ABSTRACT FROM AUTHOR]

Elemental partitioning behaviors are critical in determining the high-temperature capabilities of superalloys. In multi-component superalloys, these behaviors are influenced by the competition among elements. This study examines the effects of Cr concentration on elemental distribution behaviors and γ′ evolution in Ni–10Al–4Mo– x Cr superalloys using CALPHAD-informed phase field modeling. Our simulations show that Mo's preference shifts from γ′ precipitates to γ matrix as Cr concentration increases. This shift results from the competitive interactions between Mo and Cr atoms at the corner sites of Ni 3 Al, reducing Mo's solubility in γ′ precipitates. Further analysis reveals that with increasing Cr concentration, more Mo is displaced by Cr at the B sites of γ′-A 3 B. Additionally, the Mo content in γ′ precipitate decreases with rising Cr content, resulting in an abnormal rise in the γ′ volume fraction based on Mo mass balance. Moreover, γ′ coarsening rate initially rises and then falls with increasing Cr concentration in an inverted "V" shape, a change attributable to variations in the γ matrix supersaturation. These findings provide new insights into Mo distribution in nickel-based superalloys and offer guidance for designing superalloys with improved microstructural stability. [Display omitted] [ABSTRACT FROM AUTHOR]