High Temperature Deformation Research Articles

Analysis of dynamic recrystallization through austenite grain reconstruction of additively manufactured martensitic M789 steel

This work examines the hot compression behavior of additively manufactured M789 steel via laser powder bed fusion (LPBF) at temperatures ranging from 850 °C to 1050 °C and strain rates between 0.01 s-1 and 1 s-1. Combined corrections for friction and deformation heating were applied to the flow curves to acquire accurate stress-strain data, followed by phenomenological and physical-based constitutive modelling. In particular, the application of Sellars and Tegart hyperbolic sine model, the Kocks-Mecking model and the Johnson-Mehl-Avrami-Kolmogorov equation facilitated the development of physical material models that accurately depict the behavior of LPBF-fabricated M789 steel, highlighting the inadequacy of traditional models, such as the modified Johnson-Cook model, in capturing the complexities and metallurgical phenomena associated with high-temperature deformation. The activation energy for deformation of M789 steel was determined to be lower than that of conventional M250 steel, indicating an accelerated recrystallization process at elevated temperatures. The study also introduces a novel quantitative analysis of dynamically recrystallized grains via combined austenite parent grain reconstruction (based on the Kurdjumov-Sachs orientation relationship combined with the Markov clustering technique) and shape factor measurements, confirming the occurrence of dynamic recrystallization (DRX). The findings suggest that DRX more readily occurs at higher strain rates and higher deformation temperatures, whereas at lower temperatures, a lower strain rate is preferred to generate a higher fraction of DRX grains along with finer grains. Additionally, the work indicates that specific variants from the Kurdjumov-Sachs orientation relationship are favored during the solidification process in LPBF, which seem to disappear when the alloy is subjected to its austenitization temperature.

Finite strain, kinematic vorticity, rheological behavior and thermochronology of the Diancang Shan complex: Insights into channel flow of the southeastern Tibetan plateau

This study investigates the crustal flow within the southeastern orogenic belt of the Tibetan Plateau, with a focus on the Diancang Shan (DCS) complex. As an A-type gneiss dome, the DCS complex offers valuable insights into the deformation and evolution of intra-continental orogenic belts and the flow of deep crustal material. We have identified three main stages of deformation within the DCS complex since the Cenozoic. The initial stage (D1), spanning 41–30 Ma, was characterized by high-temperature pure shear deformation, which developed penetrative foliations, symmetric folds, and structural lenses. The subsequent major stage (D2), which shaped the overall architecture of the DCS complex from approximately 27–21 Ma, was primarily influenced by strike-slip stress regimes, resulting in shear fabrics with a top-to-the SE orientation in the releasing bend. The final stage (D3), initiated around 13 Ma, was marked by retrograde metamorphism at lower temperatures. Kinematic vorticity calculations indicate that the D1 stage was dominated by pure shear, while the D2 stage was primarily influenced by simple shear. The deformation temperature for the major deformation stage (D2) is estimated to range between 450 and 550 °C. During this stage, strain rates lie between 10−13–10−16 s−1 at 450 °C and 10−12–10−14 s−1 at 550 °C, indicating relatively low strain rates within the DCS complex. Our findings suggest that the formation of the DCS dome can be attributed to the ductile extrusion of channel flow, driven by the gravitational collapse of the Tibetan Plateau. Partial melting of the thickened middle and lower crust may have provided the channels and material sources. Furthermore, shear strain analysis (0.15–0.49) indicates that pure shear played a more significant role, contributing ∼ 65 % to the formation of the DCS dome.

Formulation of high-temperature strength equation of 9Cr-ODS tempered martensitic steels using the Larson–Miller parameter and life-fraction rule for rupture life assessment in steady-state, transient, and accident conditions of fast reactor fuel

This paper discusses the applicability of Straalsund et al.’s technique for combining the Larson–Miller parameter (LMP) and life-fraction rule to form a single high-temperature strength equation for 9Cr-oxide-dispersion-strengthened (ODS) tempered martensitic steels (TMS). It uses the extensive dataset on creep rupture, tensile, and temperature-transient-to-burst tests of 9Cr-ODS TMS cladding tubes in the α-phase, α/γ-duplex, γ-phase matrices, which are accumulated by the Japan Atomic Energy Agency so far. The technique is adequately applicable to 9Cr-ODS TMS cladding tubes. A single high-temperature strength equation expressing the mechanical strength in different deformation and rupture modes (creep, tensile, temperature-transient-to-burst) is derived for 9Cr-ODS TMS cladding tubes. This equation can predict the rupture life of the cladding tubes under various stresses and temperatures over time. The applicable range of the high-temperature strength equation is specified in this study and the upper limit temperature for the equation is found to be 1200 °C. At temperatures higher than 1200 °C, the coarsening and aggregation of nanosized oxide particles and the γ to δ phase transformation are reported in previous studies. The high-temperature strength equation can be well applied to the creep and tensile strength in the α-phase matrix, the creep strength in the γ-phase matrix and the temperature-transient-to-burst strength in both phases except for the low equivalent stress (43 MPa) at temperatures exceeding 1050 °C. The mechanism of the notable consistency between creep and tensile strength in the α-phase matrix is discussed by analyzing the high-temperature deformation data in the light of existing deformation models. The study suggested the thermal activation process is dominant even for the high-temperature deformation modes exceeding yield stress in the 9Cr-ODS TMS with the fine-grained matrix.

High-Temperature Tensile Behavior of an As-Cast Ni-W-Co-Ta Medium–Heavy Alloy

High-temperature tensile experiments with tensile rates ranging from 0.01 s−1 to 10 s−1 were carried out at various temperatures ranging from 1000 °C to 1250 °C with a Gleeble-3800 thermal simulation tester to evaluate the physical properties of an as-cast Ni–W–Co–Ta medium–heavy alloy. The microstructure evolution of the alloy during high-temperature stretching was characterized by metallographic microscopy, scanning electron microscopy, and transmission electron microscopy. The results indicated the emergence of multiple slip lines and the parallel arrangement of dislocations in the grain of the alloy after high-temperature stretching, and typical characteristics of plane slipping were observed. The plasticity of the Ni–W–Co–Ta medium–heavy alloy increased, but its strength decreased with an increase in the deformation temperature. In contrast, an increase in the strain rate resulted in a noticeable increase in the strength and plasticity of the medium–heavy alloy. The experiments revealed that the maximum tensile strength of the as-cast Ni–W–Co–Ta medium–heavy alloy was 735 MPa (T = 1000 °C, ε˙ = 10 s−1). Additionally, the maximum reduction in area and elongation was 38.1% and 11.8% (T = 1250 °C, ε˙ = 10 s−1), respectively. The mode of fracture after high-temperature tensile deformation was brittle fracturing.

АНАЛИЗ ВЛИЯНИЯ ПРЕДВАРИТЕЛЬНОЙ И ЦИКЛИЧЕСКОЙ ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ НА ХИМИКО-ТЕРМИЧЕСКУЮ ОБРАБОТКУ КОНСТРУКЦИОННЫХ СТАЛЕЙ

The subject of the study was thermodiffusion nitrided and silicified layers on steels obtained after plastic deformation. The influence of preliminary plastic deformation on the low-temperature nitriding process and cyclic plastic deformation on the high-temperature silicification process is studied. The results obtained are of interest for accelerating the production processes of chemical-thermal treatment of steels. It is established that preliminary surface plastic deformation contributes to the intensification of the process of ion-plasma nitriding of structural steel. The presence of high-temperature cyclic plastic deformation ensures the intensification of diffusion processes during the resorption of the diffusion silicified layer on structural steel.

Significant improvement of bending properties for WE43 magnesium alloys under the coupling effects of weak basal texture and high deformation temperature

Significant improvement of bending properties (approximately 64.7%) for WE43 magnesium alloy was realized by weakening the basal texture and raising the deformation temperature. The mechanisms for such improvement were investigated in detail by combining the experiment and finite element model. The results concluded that the coupling effects of weak basal texture and high deformation temperature was the key reason producing the above improvement of bending properties. Specially, the TD sample with weak basal texture was more conducive to activating basal slip than the RD sample, resulting in its higher strain hardenability and consequently more significant bending properties. Based on weak basal texture, raising the deformation temperature could further improve the bending properties. This improvement mechanism was attributed to the abundant activations of non-basal slip instead of basal slip, which could increase the independent slip systems and efficiently delay the development of the strong basal texture. Moreover, the occurrence of partial DRV and DRX relieved the stress concentrations by consuming the dislocations, further improving the bending properties. The activations of these deformation mechanisms matching the corresponding bending stress states caused the crystal rotation and the texture variety in the bending samples. Basal slip activation aligned the (0002) basal planes parallel to tensile stress in the outer region or perpendicular to compressive stress in the inner region. Additionally, prismatic slip activation induced crystal rotation around the c-axis, developing <10-10>//LD texture in the outer region but <10-10>⊥LD texture in the inner region.

Effect of Copper Powder Addition on Microscopic Deformation Behavior of Al2O3/Cu‐Dispersion‐Strengthened Copper‐Sintered Billet

In this work, it is aimed to improve the deformation ability of the Al2O3 dispersion strengthened copper sintered billet by building heterogeneous structure with addition of different sizes of particle. Using the modified mixture model and equal work law, the stress distribution model of heterogeneous materials is derived. In the results, it is shown that higher deformation temperature and lower strain rate are conducive to steady deformation. Under the conditions of 950 °C and 0.01 s−1, the stress distribution coefficients from low to high are 10, 25, and 5 μm, respectively, when the strain is 0.1. The strain contribution rates of softness of the sintered billet are 45.5%, 62.1%, and 42.6%, respectively. The addition of 10 μm particle size copper powder can significantly improve the deformation capacity of the sintered billet. It is found that with the increase of the particle size of copper powder, the density of the microgeometrically necessary dislocation of the hot extrusion dispersed copper is lower. The reason is that the different particle size of copper powder leads to the different distribution in powder stacking, which affects the difficulty of harmonizing the deformation of soft and hard and the number of dislocation in the hot‐extrusion process of sintered billet.

Study on hot compressive deformation behavior and microstructure evolution of G13Cr4Mo4Ni4V steel

To solve the problem of poor uniformity of microstructure of high alloy bearing steel G13Cr4Mo4Ni4V after rolling, the deformation behavior of the steel and its effect on the microstructure evolution was studied systematically. Gleeble-3800 thermo-mechanical simulator was used for precise control of deformation temperature ranging from 1000 to 1200 °C and deformation rate 0.01–10 s−1. Based on modified stress and strain curves by temperature and friction, the processing map of tested steel was drawn. Electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) were used to analyze the typical microstructure and carbide properties of different hot working domains respectively. The results showed the processing map could be divided into four regions: domain A 1000–1150 °C, 0.1–10 s−1; B 1000–1100 °C, 0.01–0.1 s−1; C 1100–1150 °C, 0.01–0.1 s−1 and D 1150–1200 °C, 1–10 s−1. Domain A was characterized by incomplete dynamic recrystallization (DRX) which included fine recrystallized grains and elongated deformed grains, whose softening mechanism was mainly discontinuous DRX (dDRX) and limited DRV and continuous DRX (cDRV) related to the ferrites and carbides. For domain B, the deformed grains gradually disappear with temperature rising, instead serrated grains appear with dDRX as dominating softening mechanism. A large number of carbides hinder DRX at 1000 °C with low temperature. With the increase of temperature, carbides dissolve and DRX degree increases. Grain coarsening is obvious because of high deformation temperature and low strain rate in domain C, although the nanoscale MC type carbides prevent recrystallization grain coarsening to some extent. Completely DRX resulted in uniform and fine with defect-free deformation microstructure in domain D, whose volume fraction of recrystallization reached up to 0.96 according to EBSD results. By considering the uniformity of microstructure and the distribution of carbide comprehensively, domain D is an ideal region for hot working.

Interplay between high-temperature creep deformation behavior and nanoscale precipitate evolution in a newly designed Fe–Ni-based superalloy

In an endeavor to achieve the critical goals of carbon neutrality, an explorative study was conducted to scrutinize the precipitate evolution and high-temperature creep behavior of an innovative and cost-effective Fe–Ni-based superalloy that was meticulously engineered for the next-generation ultra-supercritical (USC) power plants. The creep experiments conducted at temperatures and stresses of 650 °C/280 MPa (17,179 h), 675 °C/250 MPa (10,271 h), and 700 °C/250 MPa (2378 h), coupled with proficient data fitting were employed to accurately assess the long-term service performance of the superalloy under real-world operational environments. Though it can withstand theoretically an intense stress of 130 MPa at 700 °C for approximately 30 years as calculated by the Larson-Miller equation, its performance was not without a degree of perceived vulnerability. This was primarily traced to the conspicuous coarsening behavior of the precipitate-free zones (PFZs)/discontinuous coarsening zones (DCZs) formed in the grain boundaries (GBs) on a longer time scale. It had a significant diminishing impact on the overall strength of the GBs, resulting in a recorded creep life that was considerably shorter than initially projected. Moreover, a synergistic mechanism between PFZs/DCZs with TiC carbides was advanced to interpret the intergranular fracturing dynamic, which was postulated due to the evidence gathered from electron backscatter diffraction (EBSD), highlighting that the banded distribution of TiC carbides circumambient to GBs engendered considerable stress aggregation. Conversely, the plentiful supply of coincidence site lattice (CSL) boundaries disrupted the continuous network structure of random high-angle grain boundaries (HAGBs), thereby creating an effective barricade against the proliferation of cracks. These empirical findings paved the way for the proposition of an enhanced blueprint and the industrial utilization of such.

Evolution of Rheological and Microscopic Properties of Asphalt Binders under Fuel Corrosion

Vehicle fuel leaks can adversely affect the performance of asphalt pavements. To study the mechanisms of fuel corrosion damage in asphalt, four asphalt binders were selected in this study, and the evolution of their rheological and microscopic properties was investigated. Fuel corrosion caused continuous mass loss in asphalt binders. Base asphalt lost more than 50% of its mass after 24 h of fuel corrosion, while modified asphalts had better resistance. According to dynamic shear rheometer tests and multiple stress creep recovery tests, modifiers improved the high-temperature rheological properties of these asphalt binders. As the degree of fuel corrosion deepened, the indexes characterizing the high-temperature performance deteriorated. Rubber-modified asphalt showed the best resistance to high-temperature deformation, while the performance of LDPE-modified asphalt was more stable. In contrast, fuel corrosion improved the resistance of asphalt binders to low-temperature cracking to some extent: the creep strength (S) decreased as the creep rate (m) increased, and the resistance of SBS-modified asphalt to low-temperature cracking was optimal, with a 36% decrease in S-value after 24 h of fuel corrosion. Fourier transform infrared spectroscopy tests showed that diesel corrosion was a process of this physical dissolution, with no change in the chemical functional groups. Meanwhile, by using fluorescence images and analyzing the four-component test results, we found that fuel corrosion disrupted the stabilized structure formed by the modifiers, and the heavy components in the asphalt binders were converted into light components. This study reveals the evolution of the rheological and microscopic properties of asphalt under fuel corrosion, which can provide a reference for the optimization of fuel corrosion resistance in asphalt pavement.

Cavitation in die drawn poly(4-methyl-1-pentene) during second-stage tensile deformation

Pre-oriented poly (4-methyl-1-pentene) samples were prepared by the die drawing process. The stress whitening phenomenon induced by cavities in the different die drawn P4M1P samples during the second-stage tensile deformation was investigated at temperatures below and above Tg. At 30 °C and 50 °C, the cavitation process near yield point is influenced by the fraction of unoriented crystalline phase in pre-oriented samples. Cavities originate from the fracture of the crystalline skeleton at small strains were observed in the sample with a high fraction of unoriented crystalline phase. At high deformation temperature, the small strain cavities were suppressed and the cavitation processes in all die drawn samples are due to the failure of the highly oriented fibrillar network caused by the breaking of the load-bearing interfibrillar/microfibrillar tie molecule chains.

Redox and melting characteristics of Mn-based ores for high-temperature thermochemical energy storage

Redox and melting characteristics of Mn-based ores were investigated to test their potential use in thermochemical energy storage (TCES). Two Mn-based materials (FJ and LY) were natural ores with the Mn content higher than 35 wt%, and one Mn-based material was prepared by adding an MgO–kaolin inert support into LY ores to increase its melting temperature. Cyclic reduction and oxidation reactivity of these Mn-based materials was studied via thermogravimetric analysis (TGA), and the melting behaviors of these materials were investigated by using a melting test setup with an optical camera–image system. It was found that the oxygen capacity of the FJ Mn ore can approach ∼1.50 wt%, while the LY Mn ore had only 0.42 wt%–0.69 wt% oxygen capacity The deformation temperature of the FJ Mn ore is higher than that of the LY Mn ore, and the melting temperatures of the LY Mn ore can be significantly improved with the addition of an MgO–kaolin inert support, while the reactivity is decreased due to the addition of the MgO–kaolin inert material. This study proves that manganese ores with high oxygen capacity and deformation temperature have potential as TCES materials. For some manganese ores with low deformation temperatures, it is necessary to improve their melting temperatures and ensure oxygen capacity for high-temperature TCES applications.

Rheological performance evaluation of activated carbon powder modified asphalt based on TOPSIS method

In this study activated carbon powder (ACP) was incorporated into asphalt to substitute a portion of the conventional filler (mineral powder, MP). The dynamic modulus at elevated temperatures, temperature-dependent viscosity sensitivity, low-temperature creep, and the interaction between asphalt and ACP were examined through dynamic shear rheometer testing, viscosity testing, and bending beam rheometer testing. Moreover, statistical methodologies such as the entropy weight method (EWM) and the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) were employed to optimize the proportion of ACP by evaluating the comprehensive rheological behavior of asphalt mastic (including high temperature performance, low temperature performance, flowability, and asphalt-ACP interaction). The findings demonstrate that ACP can enhance the resistance of asphalt mastic to high-temperature deformation to a certain degree. The ratio of creep rate to stiffness (m/S) decreases with the addition of ACP, indicating that ACP may exacerbate the occurrence of low-temperature thermal cracking in asphalt mastic. The interaction ability of asphalt mastic is significantly enhanced when a portion of the filler is replaced with ACP. The loss factor shows significant impact on the comprehensive evaluation. According to TOPSIS analysis, asphalt mastic with a blending proportion of 40% ACP and 60% MP performs better in terms of comprehensive rheological properties.

Effects of Epoxy Resin Value on Waterborne-Epoxy-Resin-Modified Emulsified Asphalt Mixture Performance

Although research shows that waterborne epoxy resin emulsified asphalt (WER-EA) is an environmental protection material with potential high resistance to multiple types of pavement distress, its performance is rather complicated and much affected by the curing agent and epoxy resin value. This paper serves as a follow-up study to the preliminary published research on evaluating the impact of the epoxy value and common curing agents on the performance of asphalt mixtures. Four groups of emulsified asphalt were filtered out to prepare mixture samples, and laboratory tests on mixture performance under high and low temperatures were conducted. Specifically, Marshall and rutting tests were conducted for evaluating mixture resistance to rutting under high temperatures, and indirect tensile tests were conducted to indicate resistance to cracking at low temperatures. Water stability performance was also assessed by comparing the mixture properties before and after water absorption. The results showed that the mixture with an epoxy value of 20 and curing agents using triethylenetetramine (TETA) had the best overall performance among the investigated mixtures, with the highest resistance to high-temperature deformation and water damage. However, more research should be conducted to improve the low-temperature resistance to cracking for WER-EA mixtures.

Research on high and low temperature rheological properties of TPU/SBR composite modified asphalt

In road engineering, SBS modifier has been widely applied in China to enhance the quality of asphalt pavement. However, without considering the physical and chemical properties of SBS modifier and the asphalt substrate, alternative polymerization methods for asphalt modification that offer better performance and economic benefits have not been explored. In this study, an approach was taken to compound modify the base asphalt by incorporating Thermoplastic polyurethane (TPU) and Styrene Butadiene Rubber (SBR). The high and low temperature rheological properties of the modified asphalt were examined using tests such as Rotational Viscosity (RV) test, Dynamic Shear Rheological test (DSR), Multiple Stress Creep Rheological test (MSCR), and Bending Beam Rheological test (BBR). The modification mechanism of the mixed modified asphalt, combining SBR and TPU, was investigated through fluorescence microscope testing. The RV test revealed that the inclusion of TPU and SBR enhanced the viscosity of the asphalt to a certain extent, affording it favorable workability during construction and improved resistance against high temperature deformation. DSR and MSCR tests demonstrated that the incorporation of TPU significantly bolstered the external load resistance, deformation recovery, rutting resistance, and overall stability of the SBR modified asphalt under high temperature conditions; The BBR test proves that the composite modified asphalt has excellent low temperature crack resistance. The FM tests have shown that TPU are effective in reducing the segregation that may occur in SBR-modified asphalt, thus improving the performance of the composite modified asphalt.

Dynamic Mechanical Properties and Modified Johnson-Cook Model Considering Recrystallization Softening for Nickel-Based Powder Metallurgy Superalloys.

The material undergoes high temperature and high strain rate deformation process during the cutting process, which may induce the dynamic recrystallization behavior and result in the evolution of dynamic mechanical properties of the material to be machined. In this paper, the modified Johnson-Cook (J-C) model for nickel-based powder metallurgy superalloy considering dynamic recrystallization behavior in high strain rate and temperature is proposed. The dynamic mechanical properties of the material under different strain rates and temperature conditions are obtained by quasi-static compression test and split Hopkinson pressure bar (SHPB) test. The coefficients of the modified J-C model are obtained by the linear regression method. The modified model is verified by comparison with experimental and model prediction results. The results show that the modified J-C model proposed in this paper can accurately describe the mechanical properties of nickel-based powder metallurgy superalloys at high temperatures and high strain rates. This provides help for studying the cutting mechanism and finite element simulation of nickel-based powder metallurgy superalloy.

Optimization of the Mechanical and Corrosion Resistance of Alloy 625 through Aging Treatments

In the as-annealed condition, the nickel-based Alloy 625 has excellent mechanical and corrosion properties compared to those of common stainless steels. This peculiarity enables its exploitation in several industrial fields at cryogenic and high temperatures and in the presence of severely corrosive atmospheres. However, in this alloy, when high-temperature plastic deformation processes and heat treatments are not carefully optimized, the occurrence of excessive grain coarsening can irremediably deteriorate the mechanical strength, possibly leading to incompatibility with the standard requirements. Therefore, this research work investigated the possibility of adopting single- and double-aging treatments aimed at improving such strength loss. Their optimization involved identifying the best compromise between the hardening effect and the loss in corrosion resistance induced by the simultaneous formation of intergranular chromium-rich carbides during aging. The investigation of the aging treatments was performed using hardness, tensile and intergranular corrosion tests considering different time–temperature combinations in a range from 621 °C to 732 °C. Double aging resulted in a considerable acceleration in the hardening response compared to single aging. However, even after its optimization in terms of both temperature and time, the intergranular corrosion resistance remained a critical aspect. Among all the tested conditions, only single aging at 621 °C for 72 h was acceptable in terms of both mechanical and corrosion properties. The influence of longer exposures will be investigated in a future study.

High-temperature creep behaviour and deformation mechanism of a high-concentration Re/Ru single-crystal nickel-based alloy

In this study, the deformation and damage mechanisms of a high-concentration Re/Ru single-crystal nickel-based alloy at ultrahigh temperatures are studied via creep performance tests, microstructural observations and dislocation configuration diffraction contrast analyses at 1170 °C. The results show that the alloy has good mechanical properties. In addition, the creep life is 155 h at 1170 °C and 120 MPa. During creep, dislocations moving in the γ matrix can react with each other to form a dense and complete dislocation network. This dense and complete dislocation network can effectively prevent dislocations from shearing into the γ′ phase and reduce the creep rate during the steady-state creep period. In the late stage of ultrahigh-temperature creep, stacking faults are found in the γ′ phase, indicating that the alloy has a low stacking fault energy and that the stacking faults that form in this alloy can serve as obstacles for dislocation movement. In addition, the dislocations that cut into the γ′ phase in the late stage of ultrahigh temperature creep can cross-slip from the {111} plane to the {100} plane, forming a KW lock, which can inhibit the slip and cross-slip dislocation movement modes. Therefore, the presence of dislocation networks, stacking faults and KW locks in alloys is the main reason for the relatively low strain rate and good creep resistance of these alloys under ultrahigh-temperature creep conditions. In the late stage of creep, the initiated dislocations slip in two orientations, resulting in kinking of the rafted γ′ phase and crack initiation at the top interface of the twisted rafted γ/γ′ two phases. Under the action of shear stress, the crack generates tensile stress perpendicular to the stress axis, and it expands in this direction. This crack is the damage mechanism of the alloy during ultrahigh-temperature creep.

Segregation-induced strength anomalies in complex single-crystalline superalloys

Pushing the maximum service temperature of aircraft engines and industrial gas turbines is the major pathway to improve their energy efficiency and reduce CO2 emissions. This maximum is mostly limited by the temperature capability of key-component materials, including superalloys. In this alloy class, segregation of elements facilitates plastic deformation and is generally considered to cause softening during high-temperature deformation. Here, we show that segregation-assisted processes can also lead to strengthening and induce an anomalous increase of the yield strength. Atomic-resolution transmission electron microscopy and density functional theory calculations reveal a segregation-assisted dissociation process of dislocations at precipitate-matrix interfaces in combination with atomic-scale reordering processes. These processes lead to an inhibition of athermal deformation mechanisms and a transition to stacking fault shearing, which causes the strengthening effect. Unraveling these elementary mechanisms might guide a mechanism-based alloy design of future superalloys with enhanced high-temperature capabilities.

Analysis of Hot Tensile Fracture and Flow Behaviors of Inconel 625 Superalloy.

In this work, Inconel 625 alloy is explored regarding high-temperature tensile deformation and fracture behaviors at a strain rate of 0.005-0.01 s-1 under a deformation temperature ranging from 700-800 °C. The subsequent analysis focuses on the impact of deformation parameters on flow and fracture characteristics. The fractured surface reveals that ductile fracture is dominated by the nucleation, growth, and coalescence of microvoids as the primary failure mechanisms. The elevated deformation temperature and reduced strain rate stimulate the level of dynamically recrystallized (DRX) structures, resulting in intergranular fractures. The Arrhenius model and the particle swarm optimization-artificial neural network (PSO-ANN) model are developed to predict the hot tensile behavior of the superalloy. It indicates that the PSO-ANN model exhibits a correlation coefficient (R) as high as 0.9967, surpassing the corresponding coefficient of 0.9344 for the Arrhenius model. Furthermore, the relative absolute error of 9.13% (Arrhenius) and 1.85% (PSO-ANN model) are recorded. The developed PSO-ANN model accurately characterizes the flow features of the Inconel 625 superalloy with high precision and reliability.