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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]

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 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]

ABSTRACT High and very high cycle fatigue tests were performed to examine the microstructure and fracture mechanism of GH4169 superalloy in combination with techniques including electron‐backscatter diffraction (EBSD). Fractographic analysis revealed that surface failures are induced by surface flaws, whereas internal failures are caused by pores, facets, and inclusions. The three‐dimensional observation shows that fracture surfaces exhibit an irregular texture due to crystallographic mismatch of grains and plastic deformation at the crack tip. Based on EBSD analysis, Euler angles exhibited a complex geometry of grain orientation at the crack tip area, hindering crack propagation as evidenced by lower values of the Schmid factor and misorientation at the crack tip. Furthermore, the threshold values of small and long cracks decrease, whereas the transformation sizes from small to long crack growth increase from surface to internal failure. Finally, a novel microstructure defect‐based life prediction model is established, and the predicted results demonstrate a close resemblance to experimental outcomes. [ABSTRACT FROM AUTHOR]

The interface heat transfer coefficient (IHTC) at the different casting/shell mold interfaces during the vacuum investment casting process was investigated by measuring the temperatures of K4169 superalloy melt and mold shell during the preheating, transferring, pouring, and solidification processes. The inverse model of ProCAST was used to calculate the interface heat transfer coefficient (IHTC) based on the temperature measurement results. The inverse calculation results show that the heat transfer between the shell mold and the outside air changes from natural convection to forced convection during the transfer process, but the heat transfer between the shell mold and the inside air is consistently natural convection heat transfer. Then, the convective heat transfer coefficient gradually decreases to 0.1 W/m2·K with the vacuum increases and is finally converted to radiation heat transfer at a vacuum of 10-3 Pa. In the early stages of solidification, the IHTC between the shell mold and the casting can reach 16,000 W/m2·K due to the close contact and the large temperature difference between them, and with the thermal expansion of the shell mold and cooling contraction of the casting, the formation of the gap leads to the interfacial heat transfer coefficient gradually stabilizing at 100–200 W/m2·K. The experimental validation results show that the IHTC has a great influence on the accuracy of the prediction of the location and shape of shrinkage porosities in the vacuum investment castings. [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]

Nickel-based superalloy grinding, as well as selecting the appropriate operational parameters, is one of the major challenges in machining engineering. The conducted research consists of two sections. The first section presents a systematic experimentation, which has been carried out to qualitatively and quantitatively investigate nickel-based superalloy grinding. Vitrified CBN grinding wheels, along with a rotary diamond cup dresser, were utilised to conduct the experiments with the workpiece of Inconel 738. Specific grinding energy, G-ratio and surface roughness were indicated as three major machining outputs, while the inputs were the dressing conditioning and grinding parameters. In the following, the effects of different operational parameters were relatively ranked according to their weighted impact on the grinding performance using hybrid multi-attribute decision-making (MADM) methods. For this purpose, a combination of three techniques: Analytic Hierarchy Process (AHP), Entropy and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) was utilised to select the most appropriate grinding conditions, while considering the conflicting effect of the different dressing and grinding parameters. The results indicate that specific energy can be an important criterion for evaluating the process efficiency. The changes in G-ratio and surface roughness have the same trends, as opposed to specific grinding energy mutation. The grinding parameters are summarised in equivalent chip thickness. Our findings show that dresser cross feed rate, along with equivalent chip thickness, has the greatest impact on the grinding process efficiency. [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.

Nickel-based superalloys exhibit excellent high strength and thermal fatigue resistance at 650 ℃, making them widely used for manufacturing elevated-temperature components such as turbine blades for aero-engines. Laser-powder bed fusion (L-PBF) is a rapidly developing metal additive manufacturing technology that is increasingly important for producing nickel-based superalloy products. The design and service life of aero-engine turbine blades typically require more than 107 load cycles. Therefore, it is crucial to investigate the very-high-cycle fatigue characteristics of L-PBF nickel-based superalloys at increased temperatures. Internal failure is a common elevated-temperature fatigue mode of L-PBF nickel-based superalloys that is currently not well understood. To address this issue, first, axial fatigue tests with stress ratios of −1 and 0.1 are conducted at 650 ℃. Specifically, partial typical internal failure fractures at a stress ratio of 0.1 are selected as the focus of this study. Second, scanning electron microscopy and ultra-depth field microscopy are employed to observe the 2D and 3D morphology of the fatigue fracture surfaces and analyze the crack nucleation areas and growth paths. The results show that irrespective of the presence of defects, the emergence and aggregation of numerous facets occur in the “facetted cracking area (FCA),” a typical internal failure characteristic of L-PBF nickel-based superalloys. Measurements indicate that the size of these facets leading to cracking is comparable to that of large grains and correlates with variations in grain orientation. Therefore, internal failures are categorized into two modes of cracking: “defect-assisted faceted cracking” and “non-defect-assisted faceted cracking.” Third, the FCA exhibiting typical internal failure fractures is sectioned and subjected to electron backscatter diffraction analysis to observe surface and subsurface crystallographic features related to crack nucleation and growth behavior. The analysis reveals that microcracks mainly originate from large grains with softer orientations, propagate through slips, expand along the direction of maximum shear stress, and ultimately form a perforated fracture pattern. Fourth, subsurface microcrack features beneath the FCA are examined via focused ion beam milling and imaging. Transmission electron microscopy is then employed to observe slip bands and dislocation structures near the microcracks. The results confirm that the fatigue deformation mechanism of facets at 650 ℃ is mainly controlled by a combination of anti-phase boundary shearing, precipitate bypassing, and stacking fault shearing. This mechanism is especially evident under stress concentration effects induced by cracks or defects. Finally, according to the definition of the crack tip stress intensity factor, a crack nucleation life prediction method that accounts for the characteristics of faceted cracks is proposed. The predicted results align well with the experimental findings.

The combination of thermodynamic calculation and machine learning was used to reverse design nickel-based superalloys for thermodynamic performance requirements. The results show that the thermodynamic calculation dataset of nickel-based superalloys is successfully constructed by high-throughput thermodynamic calculations， which provides the data basis for the reverse design of nickel-based superalloys with thermodynamic performance requirements by using machine learning methods. Several C2P models are established for the thermodynamic target performance， and the accuracy of the models is higher than 99%. MLDS method is used to reverse design the alloy composition， and the eight alloys are recommended to meet the performance requirements （Vγ'，1100 ℃≥60%，Vγ，1100 ℃+Vγ'，1100 ℃≥99% and Tγ′≥1300 ℃）. The experimental verification of the three alloys with the smallest prediction error of thermomechanical properties shows that the Vγ'，1100 ℃ are greater than 80%， Vγ，1100 ℃+Vγ'，1100 ℃≥99% in the microstructure after aging， and Tγ′≥1300 ℃， which meet the design requirements.

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]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, the effects of hot isostatic pressing (HIP) and heat treatment (HT) on the stress rupture properties of nickel-based superalloy K417G were investigated. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were employed to analyze the microstructure, fracture morphology, determination of crack source and dislocation evolution after stress rupture fracture. The results indicate that, HIP specimens demonstrate a 19.5% reduction in stress rupture life compared to as-cast specimens, whereas HIP + HT specimens exhibit a 41% increase in stress rupture life, reaching a value of 63.04 h. The fracture mechanism of the samples under different heat treatment conditions is different. There are a large number of pores in the as-cast specimen, which leads to the initiation and propagation of cracks and eventually result in fracture. The pores in the HIP specimen are almost eliminated. However, the coarsening and uneven distribution of γ′ phase led to the weakening of the hindrance to dislocation movement. Additionally, the increase in elongated carbides at grain boundaries accelerates crack initiation and propagation. Under HIP and HT, the cubic γ′ phase is uniformly precipitated, which effectively hinders the movement of dislocation lines. Granular M23C6 carbides precipitate at grain boundaries, acting as pinning points to retard grain boundary sliding and crack propagation, thus improving the stress rupture life.

Mar-M247 is widely used in several fields as a material with excellent overall performance at high temperatures. However, its complex fabrication process and extremely poor weldability make it very difficult to repair and fabricate. In this study, a novel flux-cored wire with microstructures and composition similar to that of Mar-M247 nickel-based superalloy had been successfully developed, and the superalloy had been effectively repaired by cold metal transfer welding technique. Under the strict control of welding parameters, good metallurgical bonding between the weld and the base metal can be realized, and the hot cracking problem of the joint was successfully suppressed. In the weld, there were closely arranged γ′ phase precipitates with nanoscale and γ/γ′ eutectic structure, granular carbides dispersed at grain boundaries. The hardness of the weld was about 410–430 HV. It had been found that solidification cracks in welds were caused by intergranular liquid films, and grain orientation was found to be an important factor affecting solidification cracking. Optimized welding parameters of cold metal transfer could control the grain orientation of weld and reduce the size of intergranular liquid film, which could effectively suppress the size of weld solidification cracks. Additionally, liquefaction cracks were caused by eutectic reaction liquefaction in the heat-affected zone. The cold metal transfer welding process with optimized parameters can effectively reduce welding heat input, weaken eutectic reactions, and successfully obtain joints without crack in heat-affected zone.

The freckle formation and distribution in large-size directional solidified nickel-based superalloy blades at different withdrawal rates were investigated. The microstructure of freckles was analyzed by optical microscope (OM), and scanning electron microscope (SEM). The crystallographic orientation in the freckle regions was characterized by electron backscattered diffraction (EBSD). The solute segregation patterns on the surface of freckle regions were obtained by X-ray fluorescence (XRF). Numerical simulations for the temperature field were performed to analyze the mushy zone evolution during directional solidification. The experimental results indicated that the root region is prone to form freckles. The freckle chains were only distributed on the outward surface of the root region at low and middle withdrawal rates, and the inward side was free of freckles. When a high withdrawal rate was applied, a few freckles occurred on the inward side of the root region. The number and length of freckle chains increased as the withdrawal rate increased. The XRF results indicated that channel segregation formed on the surface of the root region. The segregation channels predicted by the macrosegregation simulation agreed well with the experimental observation. The concave or inclined solidification interface increased the propensity for freckle formation.

The effect of different solution temperatures (1140, 1160 ℃ and 1180 ℃) and cooling conditions (AC, FC-900 ℃+AC, FC) on the microstructures and mechanical properties of K439B alloy were investigated using metallographic microscopy and field emission scanning electron microscopy (FE-SEM). The results show that the optical microstructures and morphology of γ' precipitates are similar and the width of grain boundary slightly increases after increasing the solution temperature. When cooled with AC, γ' precipitates are uniformly distributed and the average size is 50.7 nm; when cooled with FC-900 ℃+AC, the larger γ' precipitates of 250-510 nm are precipitated at the interdendritic area region and near the grain boundary, exhibiting a bimodal γ' microstructure; when cooled with FC, the volume fraction of larger γ' precipitates increases and the content of granular M23C6 carbides at grain boundary improves. The stress rupture life of K439B alloy at 815 ℃/379 MPa is enhanced after reducing the cooling rate, while different solution parameters have little effect on the room-temperature tensile property.

Hardness reflects the comprehensive mechanical properties of materials, and its evolution during a wide temperature range reflects high-temperature performance. This study investigates the evolution of the high-temperature hardness of a nickel-based superalloy Ni16Cr13Co4Mo. Various thermal cycles featuring distinct peak heating temperatures were utilized to examine the variation of Vickers hardness with temperature. The effect of precipitated phases (specifically the γ′ phase) in the superalloy on high-temperature hardness and the deformation mechanism of the alloy was analyzed. The results show that the high-temperature hardness of the nickel-based superalloy decreases as temperature increases. However, the hardness after thermal cycles demonstrates an increase which is determined by the peak heating temperature. The increased hardness following thermal cycles is attributed to the reduction in size and the increase in the volume fraction of secondary γ′. Detailed TEM observation revealed that as the peak temperature increases, the deformation mechanism transforms from dislocation pile-ups in the γ matrix, dislocation and stacking fault shearing, microtwining in γ and γ′ phases to stacking fault shearing and piled-up dislocations in γ phase. As the result, hardness decreases as temperature increases.

By over-aging at 900 °C and 1000 °C, a high volume-fraction of η-Ni3Ti phase was prepared in a cast nickel-based superalloy with high Ti/Al ratio. EBSD analysis shows that the η phase obeys a SN-type orientation relationship with γ matrix: η//γ, {0001}η//{111}γ. Four kinds of η phase variants with a 70.5° misorientation to each other are clarified. From the η/γ interface structure as detected by HRTEM, the thin plate-like morphology of η phase is attributed to the preferential growth of the incoherent {11 2‾ 0}η//{1 1‾ 0}γ interface. The formation of η phase at the grain boundary (GB) was by a discontinuous precipitation reaction, during which the original GB migrates from the η-nucleating side into the adjacent grain following the elongation of η phase to form a cellular structure. The detailed GB migration mechanism is investigated by EBSD and rationalized from the aspect of interface energy. For the formation of η phase in grain interior, three relative reactions are clarified: (i) MC+γ→M23C6+OA-γ′, OA-γ′→η, (ii) γ→M23C6+OA-γ′, OA-γ′→η, and (iii) γ′→OA-γ′, OA-γ′→η, where OA-γ′ is the newly precipitated γ′ phase during over-aging which shares a similar elemental distribution with η. The intermediate phase OA-γ′ is formed due to the comparably low nucleation barrier from γ while its subsequent transformation to η is excited by the higher thermodynamic stability of η as revealed by the calculation results by using the VASP software. At last, as conformed by STEM-HAADF, the structure transformation of OA-γ′→η is aided by the introduce of superlattice intrinsic stacking faults.

Micro drilling using Electrical Discharge Machining (MD-EDM) has emerged as a prominent technique in precision manufacturing, offering the capability to create small and intricate holes. This study focuses on investigating the influence of input process parameters on nickel-based superalloy (Ni3 (Ti, Al)) material, while the electrode materials studied are copper, aluminum and tungsten, with varying electrode diameters of 0.4 mm, 0.5 mm and 0.6 mm. The research encompasses an L9-orthogonal array (L9-OA) in which the Machining Voltage, Peak Current (IP), Pulse off time (Poff) and Servo Standard Voltage (SVR) are varied. Three levels of Machining Voltage (4 volts, 6 volts and 8 volts) and IP are selected. Moreover, scanning electron microscope (SEM) imaging is employed to observe and analyze the morphological characteristics of the drilled holes. The experimental results reveal that the choice of electrode material and diameter significantly influences the SR of the drilled holes. Copper electrodes demonstrate the lowest SR, followed by tungsten and aluminum electrodes. Smaller electrode diameters result in improved surface finish due to reduced discharge energy concentration. Additionally, increasing the Machining Voltage leads to larger discharge energy and heat, resulting in increased SR. SEM imaging demonstrates distinct differences in hole morphology based on the electrode material and diameter, with copper electrodes producing cleaner and more precise holes with minimal recast layer formation compared to aluminum and tungsten electrodes. The influence of Machining Voltage is observed through the presence of craters and debris in higher voltage conditions.

The application potential of additive manufacturing nickel-based superalloys in aeroengines and gas turbines is extensive, and evaluating their mechanical properties is crucial for promoting the engineering application in load-bearing components. In this study, Hastelloy X alloy was prepared using the laser powder bed fusion process combined with solution heat treatment. The tensile and high cycle fatigue properties were experimentally investigated at room temperature as well as two typical elevated temperatures, 650 °C and 815 °C. It was found that, during elevated-temperature tensile deformation, the alloy exhibits significant serrated flow behavior, primarily observed during the initial stage of plastic deformation at 650 °C but occurring throughout the entire plastic deformation process at 815 °C. Notably, when deformation is small, sawtooth fluctuations are significantly higher at 815 °C compared to 650 °C. Irregular subsurface lack of fusion defects serve as primary sources for fatigue crack initiation in this alloy including both single-source and multi-source initiation mechanisms; moreover, oxidation on fracture surfaces is more prone to occur at elevated temperatures, particularly at 815 °C. [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]

Serrated flow phenomenon has been widely observed among different metals due to the potential influence on their applications. Uniaxial tensile tests of nickel-based superalloy GH536 were carried out at loading rates of 0.06, 0.60, 3.60, and 36.00 mm·min−1 at room temperature, respectively. The tensile stress–strain curves demonstrate repetitive and discontinuous yielding behavior, namely serrated flow. It is observed that the stress–strain curves were dominated by type B serration, and original annealing twin boundaries (TBs) were distorted to various degrees under comparatively different lower tensile rates. In contrast, the TBs almost disappear, and the type B serrations become smoother and regular under the higher loading rates. This phenomenon can be attributed to the interactions between TBs and dislocations during tensile deformation. Coupled effects of the mobile and immobile dislocations illustrate the unsteady amplitude of serrations observed in stress–strain curves. Transmission electron microscope images of tested pieces reveal the interaction of dislocation and TB, with dislocation tangling around the TBs. [ABSTRACT FROM AUTHOR]

Nickel-based superalloys are extensively used in the crucial hot-section components of industrial gas turbines, aeronautics, and astronautics because of their excellent mechanical properties and corrosion resistance at high temperatures. Fusion welding serves as an effective means for joining and repairing these alloys; however, fusion welding-induced liquation cracking has been a challenging issue. This paper comprehensively reviewed recent liquation cracking, discussing the formation mechanisms, cracking criteria, and remedies. In recent investigations, regulating material composition, changing the preweld heat treatment of the base metal, optimizing the welding process parameters, and applying auxiliary control methods are effective strategies for mitigating cracks. To promote the application of nickel-based superalloys, further research on the combination impact of multiple elements on cracking prevention and specific quantitative criteria for liquation cracking is necessary. [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]

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Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Out of all the mechanical energy generated during material cutting, the majority is converted into heat, raising the temperature at the chip-tool interface, particularly in difficult-to-machine materials like Inconel 718, thereby diminishing tool lifespan. Consequently, various lubri-cooling methods mitigate issues related to high temperatures, such as reduced tool life and geometric distortions. The most employed method is cutting fluids application (CFA), but this approach poses several problems, including high cost and environmental and operator hazards. As a result, several techniques have been developed to lower machining temperatures, such as minimum quantity lubrication (MQL), cryogenics, and indirect tool cooling. In this study, an innovative method of tool cooling via internally cooled tool (ICT) was devised and tested. In this approach, the cooling fluid circulates in a closed loop without direct contact with the workpiece or even any fluid dispersion to the atmosphere, increasing environmental appeal and reducing manufacturing coasts. The developed method was compared with temperature measurements taken through thermography and a tool-workpiece thermocouple during the turning of Inconel 718. Two factorial designs studied temperature in Inconel 718 turning via thermocamera and tool-workpiece thermocouple. Additionally, the tool coating (TiNAl or AlCrN + TiNAl), cutting speed, feed, and depth of cut were varied. Using the tool-workpiece thermocouple method, ICT and CFA did not observe any statistically significant temperature difference. However, between ICT and DM, ICT exhibited a lower temperature at the tool-workpiece interface. With thermal imaging, ICT displayed a lower chip temperature than DM. In sum, internally cooled tools emerge as an innovative and environmentally sustainable solution for machining Inconel 718. They offer outstanding heat removal capabilities and substantial advantages over cutting fluids while significantly surpassing the performance of dry machining, thereby addressing crucial concerns in sustainable machining practices. [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]

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]

In this study, the effect of adding different contents of yttrium (Y) during vacuum induction melting in Al2O3 and Y2O3 crucibles on the purification of DD5 alloys was investigated. The results show that the Y2O3 crucible exhibited great crucible stability and an excellent desulfurization effect when melting a Y-containing DD5 alloy. The S content of the alloy was reduced from 5.03 ppm to 1.36 ppm with the addition of 0.50 wt.% Y. Element Y combined with free S in the melt to form the YS phase, which was removed from the condensate shell and slag during the vacuum induction melting (VIM) process. Meanwhile, when the alloy was melted in the Y2O3 crucible with 0.50 wt.% Y addition, there was a reduction in S content from 2.77 ppm to 1.36 ppm compared to the Al2O3 crucible. Additionally, the loss of Y decreased from 0.12 wt.% to 0.05 wt.%. [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]

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]