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The flow softening behaviors of a nickel-based superalloy with δ phase are investigated by hot compression tests over wide ranges of deformation temperature and strain rate. Electron backscattered diffraction (EBSD), optical microscopy (OM), and scanning electron microscopy (SEM) are employed to study the flow softening mechanisms of the studied superalloy. It is found that the flow softening behaviors of the studied superalloy are sensitive to deformation temperature and strain rate. At high strain rate and low deformation temperature, the obvious flow softening behaviors occur. With the increase of deformation temperature or decrease of strain rate, the flow softening degree becomes weaken. At high strain rate (1s−1), the flow softening is mostly induced by the plastic deformation heating and flow localization. However, at low strain rate domains (0.001-0.01s−1), the effects of deformation heating on flow softening are slight. Moreover, the flow softening at low strain rates is mainly induced by the discontinuous dynamic recrystallization and the dissolution of δ phase (Ni3Nb).

In this study, the continuous dynamic recrystallization (CDRX) behaviors of a hot-deformed Ti-55511 alloy are investigated in β single-phase domain. CDRX is found to play a dominant role in the microstructure evolution during thermomechanical forming of the Ti-55511 alloy. In order to quantitatively and visually simulate the hot forming process, a probabilistic cellular automata (CA) method is established. This CA technology integrates the dislocation evolution model, subgrain nucleation rate model, misorientation evolution model, grain boundary (GB) migration model, and topology deformation model. The results of a systematic study of both microstructural evolution and macroscopic mechanical response at various strains, strain rates, and temperatures are presented. The average absolute relative error (AARE), correlation coefficient (R), and root-mean squared error (RMSE) values between the experimental and simulated stresses are 4.63 %, 0.9963, and 3.81 MPa, respectively. The deviation values of subgrain size range from 1.27 % to 17.25 %, when the temperatures varies from 920 to 980 °C. The predicted results well agree with the measured results, demonstrating the transition from a coarse and static recrystallized structure to a refined and continuous dynamic recrystallized structure. A low Zener-Hollomon (Z) parameter can effectively enhance the progress of CDRX. Higher temperatures and lower strain rates result in a larger volume fraction of CDRX. Quantitative analyses confirm that the incubation period for CDRX is significantly longer than that for subgrain formation, indicating a sustained transformation from the low-angle grain boundaries (LAGBs) to the high-angle grain boundaries (HAGBs) through the absorption of dislocations. • A probabilistic CA model is developed to study continuous dynamic recrystallization (CDRX) behaviors of a Ti alloy. • Coarse and static recrystallized structures are transformed to refined and CDRX structures. • A low Zener-Hollomon (Z) parameter can effectively enhance the progress of CDRX. • The subgrain size depends on the Z parameter and follows an inverse logarithmic relationship. • The incubation period for CDRX is significantly longer than that for subgrain formation. [ABSTRACT FROM AUTHOR]

The precipitation behavior of α phase in a β-quenched Ti-55511 alloy during high-temperature compression is investigated. The influences of deformation parameters on the flow characteristics, microstructural evolution, as well as the precipitation behavior of α phase, are discussed. Results show that the flow stress features and the dominant softening mechanism are sensitive to the deformation parameters. At low strain rates or high deformation temperatures, the main softening mechanism is dynamic recovery. But, the dynamic recrystallization becomes the dominant softening mechanism at high strain rates or low temperatures. At low strain rates, the continuous strengthening, induced by the pinning effect of α precipitates, happens at the late period of deformation. Distribution of α precipitates is not greatly affected by deformation parameters. In the region near β grain boundary, α precipitates are densely distributed with few orientations. While in the central region of β grain, the α precipitates are distributed a bit more sparsely with several scattering orientations. In addition, with increasing deformation temperature, the content, aspect ratio and size of α phases decrease. However, with increasing strain rate, the content, aspect ratio and size first increase and then decrease. Furthermore, the peak value of aspect ratio appears at 0.01 s−1. • Precipitation behavior of α phase in a β-quenched Ti-55511 alloy during hot compression is studied. • At low strain rates or high deformation temperatures, the main softening mechanism is dynamic recovery. • Dynamic recrystallization is the dominant softening mechanism at high strain rates or low temperatures. • α precipitates are distributed a bit more sparsely with several scattering orientations within β grains. • With increasing deformation temperature, the content, aspect ratio and size of α phases decrease. [ABSTRACT FROM AUTHOR]

Abstract Microstructural changes and flow characteristics of a nickel-based superalloy with pre-precipitated δ phases (Ni 3 Nb) are investigated using hot compressive experiments. The higher forming temperature or lower strain rate not only aggravate the arrangement/annihilation of dislocations, but also stimulate the generation/growth of substructures and dynamic recrystallization (DRX) grains. As the percentage of pre-precipitated δ phases is raised, the obvious work hardening behavior induced by the intense interactions between δ phases, grain boundaries and substructures occurs in the initial hot forming process. While the alloy is further strained, the DRX behavior are obviously promoted by δ phases. Considering the influences of pre-precipitated δ phases and forming parameters, an improved Hensel-Spittel-Carofalo (HSC) equation and an e -insensitive support vector regression (e-SVR) model are developed for reconstructing the flow features of the researched alloy. The minor deviations between the tested and forecasted true stresses indicate that the developed HSC model and e -SVR model can be properly utilized to characterize the hot forming features of the researched superalloy with different percentages of pre-precipitated δ phases. Highlights • Hot forming behaviors of a nickel-base alloy with different pre-precipitated δ phase (Ni3Nb) are investigated. • Effects of forming parameters and δ phase on flow features and microstructural variations are significant. • Evolution of substructures is weaken at higher strain rate, while becomes obvious at higher forming temperature. • The increased pre-precipitated δ phase can aggravate the nucleation of substructures and DRX grains. • Flow features with pre-precipitated δ phase can be precisely reconstructed by HSC and e -SVR models [ABSTRACT FROM AUTHOR]

High-temperature compressive experiments of a Ni-based superalloy containing δ phase (Ni 3 Nb) are conducted. The dynamic dissolution behavior of δ phase in hot deformation process is quantitatively investigated. The dissolution mechanisms of δ phase are analyzed by Transmission Electron Microscopy (TEM) and first-principles calculations. Results reveal that the dissolution of δ phase is accelerated with increasing deformation temperature or deformation degree. But, the dissolution of δ phase becomes weaken as the strain rate is raised. The shear modulus ( G ) and bulk modulus ( B ) of δ phase decrease with increasing temperature or reducing pressure. The positive Cauchy pressure ( C 12 – C 44 ) and the larger ratio of B/G (greater than 1.75) reveal that δ phase is ductile at high temperatures or pressures. The intense interactions between dislocations and δ phase induce the stress concentration and the rapid diffusion of Nb atoms, which accelerate the precipitation/dissolution of δ phase. A phenomenological model is established for depicting the dissolution behavior of δ phase in hot deformation process. The measured results are identical with the forecasted ones, which demonstrates the established model is feasible to accurately depict the dynamic dissolution behaviors of δ phase in hot deformation process. [ABSTRACT FROM AUTHOR]

The hot deformation characteristics of a nickel-base alloy with different contents of δ phase (Ni 3 Nb) were studied by isothermal compressive experiments. The experimental data and microstructural observation reveal that the hot compressive behavior and dislocation substructure evolution not only relate to the thermomechanical parameters (deformation temperature, strain, strain rate), but also are affected by the content of δ phase. In the initial deformation stage, the dislocation movement is significantly impeded, and the strain hardening behavior is aggravated with increasing the content of δ phase. With the further straining, δ phase exerts the ability for promoting dynamic recrystallization (DRX). Additionally, a new phenomenological constitutive model (PCM) and a deep belief network model (DBNM) are developed to reflect the influence of δ phase. The relative coefficients of the developed PCM and DBNM are 0.992 and 0.998, respectively. The error bands of flow stresses predicted by PCM and DBNM are controlled in ±30 MPa and ±20 MPa, respectively. The high predictability indicates that the developed PCM and DBNM can quantitatively reflect the hot deformation behaviors of the studied alloy with different δ phase contents. [ABSTRACT FROM AUTHOR]

The high-temperature flow characteristics and microstructural changes of alloys are usually investigated by isothermal compressive experiments at constant strain rates. However, during the practice industrial production of components, the strain rate is varying. In the present work, the microstructure changes and high-temperature flow characteristics of a Ni-based superalloy containing δ phases were researched by isothermal two-stage high-temperature compression experiments with stepped strain rates. It is revealed that the true stress of the later stage distinctly increases when the true strain/strain rate of the former stage or the strain rate of the later stage are raised. Meanwhile, the dynamic recrystallization (DRX) grains become finer, and the dissolution of δ phase is weakened. But, the coarsening of DRX grains and the dissolution of δ phase are enhanced as the deformation temperature is raised. The primary DRX nucleation mechanism is the discontinuous DRX. Based on the measured flow stress, an e -insensitive support vector regression ( e -SVR) model is established for depicting the flow behavior of the researched alloy. The measured results are consistent with the forecasted ones, which illustrating that the developed e -SVR model is feasible to accurately describe the flow behaviors of the researched alloy during two-stage high-temperature deformation with stepped strain rates. [ABSTRACT FROM AUTHOR]

The metadynamic recrystallization (MDRX) behaviors of a solid-solution GH4169 superalloy were studied by two-pass hot compression tests. The effects of pre-strain (deformation degree of the first pass) on MDRX behaviors were analyzed. Results show that the MDRX behaviors intensely depend on the pre-strain. The MDRX fraction first increases and then drops with the increased pre-strain. This is because a relatively large pre-strain can facilitate the nucleation of dynamic recrystallization (DRX) grains, which promotes the subsequent MDRX behaviors. However, due to the decreased stored deformation energy at relatively high pre-strain, the number of DRX grains cannot continuously increases. Thus, the MDRX fraction is reduced with the further increase of pre-strain. The segmented MDRX kinetics models were proposed and validated to describe the significant strain dependence of MDRX behaviors. [ABSTRACT FROM AUTHOR]

Isothermal compressive tests of a new hot isostatic pressed (HIPed) powder metallurgy (P/M) superalloy are performed at diverse deformation amounts, strain rates, and elevated temperatures. The impacts of hot compression parameters on the morphological evolution and dissolution behavior of γ' phase are studied. Results show that the morphology of γ′ phase changes from the various initial shapes (irregular, split-off branch, dendrite, butterfly-like, and cauliflower) to spherical, due to the overlap of the γ'/γ interface energy and the coherent strain energy related to lattice misfit. Besides, the dislocation accumulation leads to the increased local stress and enhances the spheroidization behavior of γ' phase. Increasing temperature/true strain or decreasing strain rate, the dynamic dissolution behavior of γ' phase is obvious. It is because the dislocation/ vacancies-assisted element diffusion is rapid at high deformation temperatures/true strains, and the low strain rate can provide the enough time for element diffusion. The substantial dissolution of γ' phase at 1140 °C and 1170 °C is also related to the deformation temperature approaching and exceeding the γ' solvus temperature (1150 °C), respectively. Additionally, the decreased fraction of γ' phase is also related to the high γ'/γ interfacial energy. To quantitatively describe the dissolution behavior of γ′ phase, a dynamic dissolution kinetics model is proposed, and the correlation coefficient between the predicted and experimental values is 0.990. It indicates that the proposed model can precisely depict the dissolution behavior of γ′ phase. The findings in this work can provide the theoretical guidance to optimize deformation parameters, as well as control the morphology and fraction of γ′ phases. • Dissolution and spheroidization mechanisms of γ′ phase in a novel HIPed P/M superalloy during hot deformation are studied. • The morphology of γ′ phase changes from the various initial shapes (irregular, split-off branch, et al.) to spherical. • The spheroidization of γ' phase mainly results from lattice misfit and the interaction between dislocation and γ' phase. • The dynamic dissolution behavior of γ' phase is obvious with increasing temperature/strain or decreasing strain rate. • The proposed dynamic dissolution kinetics model can precisely depict the dissolution behavior of γ′ phase. [ABSTRACT FROM AUTHOR]

The isothermal compressive tests with strain rates of (0.001–1) s −1 and deformation temperatures of (920–1040) °C were conducted to study the high-temperature deformation behavior of a Ni-based superalloy. The experimental results show that the true stress decreases with increasing deformation temperature or decreasing strain rate. The effects of deformation temperature and strain rate on dislocation substructures are significant. Based on the experimental data, an adaptive-network-based fuzzy inference system (ANFIS) model is constructed for describing the high-temperature deformation behavior of the studied Ni-based superalloy. The inputs of the constructed ANFIS model are deformation parameters (deformation temperature, strain rate and true strain), while the output is true stress. The optimal numbers and types of membership function for the above three input variables are 5-4-5 and ‘triangle-shape, triangle-shape, bell-shape’, respectively. Comparing the experimental and predicted results, it is found that the constructed ANFIS model can be used to accurately predict the high-temperature deformation behavior of the studied Ni-based superalloy. [ABSTRACT FROM AUTHOR]

A 2D cellular automaton model (CA) is developed to predict the hot deformation behavior of a Ni-based superalloy over a wide range of thermal-mechanical conditions. Relationships between the model parameters (work hardening parameter, dynamic recovery parameter, nucleation rate, and grain boundary mobility) and the thermal-mechanical conditions are established. The developed CA model is further employed to study the hot deformation behavior of the studied superalloy under varying thermal-mechanical conditions. These varying conditions include the sudden change of strain rate and gradual change of deformation temperature. The evolutions of flow stress, average grain size and fraction of dynamic recrystallization (DRX) under the varying thermal-mechanical conditions are predicted. The reliability of the simulated results is verified by experimental results. It is found that the predicted results under varying thermal-mechanical conditions gradually approach those under constant hot deformed conditions. i.e., constant deformation temperature and strain rate. The varying thermal-mechanical condition makes the complex evolution of dislocation density, fraction of DRX, and average grain size. Additionally, a pseudo-metadynamic recrystallization is found. The pseudo-metadynamic recrystallization is a temporary suspension of dynamic recrystallization during a large and rapid increase of strain rate as a consequence of nucleation inhibition. It resembles metadynamic recrystallization, except that the pseudo-metadynamic recrystallization occurs when the hot deformation is still underway. [ABSTRACT FROM AUTHOR]

To investigate the hot deformation behaviors of a nickel-based superalloy, the hot compressive tests are conducted at the deformation temperature range of 920–1040 °C and strain rate range of 0.001-1s −1 . It is found that the effects of strain rate and deformation temperature on the grain boundary maps are significant. An almost competed dynamic recrystallization (DRX) microstructure occurs at relatively low strain rates. However, the increased strain rate easily leads to the uneven microstructures. The DRX degree notably increases with the increase of deformation temperature, because the high temperature enhances the grain boundary migration mobility and facilitates the nucleation and growth of DRX grains. Based on the experimental results, multi-gene genetic programming (MGGP), artificial neural network (ANN) and Arrhenius type phenomenological models are established to predict the flow stress. Due to the obvious over-fitting problem of MGGP model, a Hannan-Quinn information criterion based MGGP (HQC-MGGP) approach is proposed. The performances of MGGP, HQC-MGGP, ANN and phenomenological models are compared. It is found that HQC-MGGP model has the best performance to predict the flow stress under the experimental conditions. Therefore, HQC-MGGP model is accurate and reliable in describing the hot deformation behaviors of the studied nickel-based superalloy. [ABSTRACT FROM AUTHOR]

Hot compression tests of a nickel-based superalloy with δ phase (Ni 3 Nb) are performed. The evolution of dynamic recrystallization (DRX) grains and δ phase, as well as the interactions between DRX grains and δ phase, is investigated. It is observed that the fraction of high-angle grain boundaries significantly increases with the increased true strain or the decreased strain rate. This attributes to the obvious DRX nucleation at relatively low strain rates or large true strains. The fraction of high-angle grain boundaries firstly increases, and then decreases when the temperature is increased. It is related to the fact that δ phases sharply dissolute as the deformation temperature exceeds 980 °C, and the restricting effects of δ phases on the growth of DRX grains are significantly weaken. Meanwhile, the initial needle-like δ phases experience the distortion, dissolution and transformation into the rod-like δ phases during hot compression deformation. Besides, δ phase can easily induce high density dislocation cells, which accelerates the formation and rotation of subgrains. So, nucleation of DRX is stimulated by δ phase. [ABSTRACT FROM AUTHOR]

Hot deformation behaviors of two pre-treated nickel-based superalloys are investigated over wide ranges of strain rate and temperature. Based on the theory of dynamic material model (DMM), the processing maps are developed and correlated with the deformed microstructures. The effects of pre-treatment, including water-cooling and furnace-cooling pre-treatments, on the hot deformation behavior and processing maps are discussed in detail. It is found that the hot deformation behavior and processing map of the aged superalloy are sensitive to pre-treatment. The peak stress of the aged superalloy after furnace-cooling pre-treatment is larger than that after water-cooling pre-treatment. Considering the coupled effects of deformation temperature, strain and strain rate, the phenomenological constitutive models of two pre-treated nickel-based superalloys are established. Meanwhile, the flow instability domains of the aged superalloy after furnace-cooling pre-treatment are narrower than those after water-cooling pre-treatment. At the true strain of 0.6, the flow instability domain of the aged superalloy after water-cooling pre-treatment is (920–1010 °C, 0.1–1s −1 ), while that after furnace-cooling pre-treatment is (930–970 °C, 0.1–1s −1 ). Additionally, the dynamic recrystallized grain size of the studied superalloy after furnace-cooling pre-treatment is smaller than that after water-cooling pre-treatment. [ABSTRACT FROM AUTHOR]

Hot deformation behaviors of a typical nickel-based superalloy are investigated by isothermal compression tests under the deformation temperature range of 920–1040 °C and strain rate range of 0.001–1 s −1 . Scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) technique and transmission electron microscopy (TEM) are employed to study the evolution of hot deformed microstructures. It is found that the fraction of low angle grain boundaries decreases with the increase of deformation temperature or the decrease of strain rate. This is related to the decrease of dynamic recrystallization degree under the low deformation temperature or high strain rate. The fraction of low angle grain boundaries shows a rapid increase at the relatively small deformation degree, and then a significant decrease due to the progress of dynamic recrystallization (DRX). The microstructural changes indicate that both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) take place during hot deformation. However, the small fraction of low angle boundaries with 10–15° misorientation indicates that the CDRX plays a minor role on the nucleation of dynamic recrystallization. Discontinuous dynamic recrystallization (DDRX) characterized by grain boundary bulging is the dominant nucleation mechanism for the studied superalloy. [ABSTRACT FROM AUTHOR]

Hot compressive tests of a nickel-based superalloy are performed under the strain rate range of 0.001–1 s − 1 and deformation temperature range of 920–1040 °C. Optical microscopy (OM) and transmission electron microscopy (TEM) are employed to investigate the evolution of dynamic recrystallized (DRX) grain and dislocation substructure. It is found that the effects of deformation degree, strain rate and deformation temperature on DRX grain are significant. When the deformation degree or temperature is increased, the number of DRX grains rapidly increases. But, the increase of strain rate reduces the number of DRX grains. The dislocation substructure is also very sensitive to the deformation degree, strain rate and deformation temperature. With the increase of deformation degree, the evolution of dislocation substructure can be characterized as: high dislocation density → dislocation network → subgrain → DRX grain. Under high deformation temperatures or low strain rates, the dislocation substructure can be easily annihilated and rearranged because of the occurrence of DRX. Based on the evaluated DRX volume fractions, the contour map is constructed to optimize the hot deformation parameters. [ABSTRACT FROM AUTHOR]

Hot deformation behavior of an aged inconel 718 superalloy is investigated by isothermal compression tests over wide ranges of strain rate and deformation temperature. In this study, the effects of hot deformation parameters (deformation temperature and strain rate) on flow stress are analyzed. It is found that the flow stress of the studied superalloy is significantly affected by deformation temperature and strain rate. The flow stress decreases with the decrease of strain rate or the increase of deformation temperature. Based on the experimental results, a new constitutive model is developed to describe the hot deformation behavior. For the work hardening-dynamic recovery stage, an isotropic internal variable is used to represent the plastic deformation resistance, and a viscoplastic constitutive model is developed to describe the work hardening and dynamic recovery behavior. For the dynamic softening stage, the phenomenological constitutive models, which consider the coupled effects of deformation temperature, strain rate and strain on hot deformation behavior, are developed. The predicted flow stresses are in a good agreement with the experimental ones, indicating that the developed models can accurately characterize the hot deformation behavior of the studied Ni-based superalloy. [ABSTRACT FROM AUTHOR]

Highlights: [•] The hot deformation behavior of a typical nickel-based superalloy is investigated. [•] The obvious dynamic recrystallization occurs under high temperature and low strain rate. [•] A physically-based constitutive model is developed for the studied nickel-based superalloy. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hot tensile deformation behavior of a typical Al–Cu–Mg alloy are studied. [•] A new phenomenological constitutive model is proposed to describe the hot deformation behavior. [•] The coupled effects of processing parameters on hardening and softening mechanisms are considered. [ABSTRACT FROM AUTHOR]

Abstract: The high-temperature flow behavior of Al–Cu–Mg alloy is studied by the hot compressive tests over wide range of strain rate and forming temperature. Considering the negative effects of the interfacial friction on the heterogeneous deformation of specimen, the measured flow stress was corrected. The effects of processing parameters on material flow behavior are discussed. Based on the measured stress–strain data, a phenomenological constitutive model, which considers the coupled effects of strain, strain rate and forming temperature on the flow behavior of alloy, was proposed to describe the compressive behavior of the studied Al–Cu–Mg alloy. The proposed constitutive model correlates well with the experimental results, which confirms that the proposed model can give an accurate and precise estimate of flow stress for the studied Al–Cu–Mg alloy. [Copyright &y& Elsevier]

Abstract: The compressive deformation behaviors of 2124-T851 aluminum alloy were investigated over a wide range of temperature and strain rate on Gleeble-1500 thermo-simulation machine. The results show that the true stress–true strain curves exhibit a peak stress at a very small strain, after which the flow stresses decrease until high strains, showing a dynamic flow softening. The measured flow stress was modified by friction correction, and the corrected flow stresses are lower than the measured ones, which nicely reflect negative effects of the interfacial friction on the flow stress. A revised model is proposed to describe the relationships of the flow stress, strain rate and temperature of 2124-T851 aluminum alloy at elevated temperatures. The stress–strain values of 2124-T851 aluminum alloy predicted by the proposed model well agree with experimental results, which confirmed that the revised deformation constitutive equation gives an accurate and precise estimate for the flow stress of 2124-T851 aluminum alloy. [ABSTRACT FROM AUTHOR]

Abstract: Numerical simulations can be truly reliable only when a proper material flow stress relationship is built because of its effective role on metal flow pattern as well as the kinetics of metallurgical transformation. Based on the hot compressive deformation behaviors of 42CrMo steel, a comprehensive constitutive model has been developed to predict stress–strain curve up to the peak stress. A new material parameter , which is sensitive to the forming temperature and strain rate, was proposed in the developed constitutive model. Additionally, the mathematical models to predict peak stress and peak strain were established based on experimental results. The stress–strain values predicted by the developed model well agree with experimental results, which confirmed that the developed constitutive equation gives an accurate and precise estimate for the flow stress of 42CrMo steel. [Copyright &y& Elsevier]

Abstract: Based on the experimental results from the hot compression tests of 42CrMo steel, the efficiencies of power dissipation and instability parameter were evaluated. The effects of strain on the efficiency of power dissipation and instability parameter of 42CrMo steel have been discussed in detail. Processing maps were constructed by superimposition of the instability map over the power dissipation map. The dynamic recrystallization domains and instable zones were identified in the processing map. The effects of strain on microstructural evolutions were correlated with the processing maps. According to the 3D processing maps, the optimum domain of hot deformation is in the temperature range of 1050–1150°C and strain rate range of 0.01–3s−1, with its peak efficiency of 32% at about 1140°C and 0.23s−1, which are the optimum hot working parameters. [Copyright &y& Elsevier]

The precipitation orientation of α phases in a Ti-55511 alloy during the heat treatment and the subsequent hot deformation is investigated. It is observed that the β grains prominently influence the precipitation process of α phases, i.e., for the neighbouring β grains without similar {110} pole, the precipitation orientation of grain boundary (GB) α phases (α GB) keep {0001}//{110}β1 or {0001}//{110}β2 to maintain the burgers orientation relationship (BOR) with the neighbouring β grains. For the neighbouring β grains with similar {110} pole, the {0001} poles of α GB phases precipitate parallel to this similar {110} pole and maintain BOR with the neighbouring β grains. For the neighbouring β grains with multiple similar {110} poles, the {0001} poles of α GB phases precipitate along these similar poles and maintain BOR with the neighbouring β grains. Besides, the interface instability nucleation and sympathetic nucleation are the main nucleation modes of the GB widmanstatten α phase (α WGB), which primarily precipitate within β grains with the similar orientation of α GB phases. The intracrystalline widmanstatten phase (α WI) precipitate in a single β grain with 12 precipitation orientations. The BOR between α WI phases and β grains is destroyed during the subsequent hot compressive deformation. • Precipitation orientation of α phases in Ti-55511 alloy during heat treatment plus hot deformation is studied. • Precipitation orientation of GB α phases maintains the BOR with neighbouring β grains along different poles. • Interface instability and sympathetic nucleations are the main nucleation modes of GB widmanstatten α phases. • The intracrystalline widmanstatten phases (α WI) precipitate in a single β grain with 12 precipitation orientations. • The BOR between α WI phases and β grains is destroyed during the subsequent hot compressive deformation. [ABSTRACT FROM AUTHOR]

Hot tensile tests are performed on an Al-Zn-Mg-Cu alloy at larger temperature and strain rate ranges. The influences of deformation parameters and stress triaxiality on hot tensile fracture characteristics, fracture mechanisms and microstructural evolution are discussed. It is found that the maximum tensile load increases with raising stress triaxiality. The fracture strain rises with increasing strain rate or decreasing stress triaxiality. When the deformation temperature is raised, the fracture strain firstly increases and then decreases. Dynamic recovery (DRV) is the main softening mechanism. At low strain rates or high deformation temperatures, the partial dynamic recrystallization (DRX) behavior occurs, and continuous dynamic recrystallization (CDRX) is the main DRX mode. The dominant fracture mechanism is the coalescence of micro-voids at the tested deformation conditions. Due to the occurrence of DRX, the intergranular fracture also occurs at low strain rates or high deformation temperatures. The low strain rate or high stress triaxiality easily induces the appearance of micro-voids, which accelerate the fracture failure. • Effects of deformation conditions and stress triaxiality on hot tensile fracture features and microstructures are studied. • The fracture strain rises with increasing strain rate or decreasing stress triaxiality. • At low strain rates or high temperatures, continuous dynamic recrystallization (CDRX) is the main DRX mode. • Dominant fracture mechanism is the coalescence of micro-voids at the tested deformation conditions. • Low strain rate or high stress triaxiality easily induces the appearance of micro-voids, accelerating the fracture. [ABSTRACT FROM AUTHOR]

Hot deformation behaviors of a solution-treated Ni-based superalloy are investigated. There are two types of hot compressive tests. Type A means that the strain rate keeps constant, while Type B denotes that the strain rate firstly keeps a high value in stage I, then a low one in stage II. It can be found that the deformation parameters and deformation history have great effects on the flow behavior. There is a sudden change in the true stress of type B when the strain rate is suddenly decreased. Comparing to the flow stress curve of types A and B, it is found that the stress of type B is slightly higher. However, the difference in the true stress between type A-II and type B gradually decreases and eventually disappears. The microstructural evolution is also significantly influenced by deformation parameters. Firstly, it is beneficial to increase deformation temperature or decrease strain rate for dynamic recrystallization (DRX). Secondly, both the average DRX grain size and misorientation angle are positively correlated with deformation temperature while negatively correlated with strain rate. Besides, the average D R X grain size of type B is between that of types A-I and A-II, so do the fraction of D R X . [ABSTRACT FROM AUTHOR]

The microstructural evolution of an aged Ni-based superalloy under two-stage hot compressive deformation with different strain rates is investigated. In terms of strain rate, the hot compressive tests include two types: constant and stepped strain rates. For the first type, the strain rate remains constant during the whole hot compression, while for the second type, the hot compression process consists of two stages: I and II. Moreover, the strain rate of stage I (0.01, 0.1, and 1 s − 1 ) is larger than that of stage II (0.001 s − 1 ). It is found that the strain rate and strain of stage I greatly affect the microstructural evolution for the hot compressive deformation with stepped strain rates. In the tested strain rate and strain, both the dissolution rate of δ phase and the dynamic recrystallization (DRX) volume fraction increase with the decrease of strain rate or the increase of strain in stage I. Compared with the constant strain rate hot deformation, the stepped strain rates can obviously promote DRX behaviors and the dissolution of δ phase if the appropriate strain rate and strain of stage I are chosen. These findings can be directly applied in the practical industrial production of superalloy components. [ABSTRACT FROM AUTHOR]