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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 texture evolution of a near β-Ti alloy (Ti-55511) is investigated by hot compressive deformation experiments in β region. A visco-plastic self-consistent (VPSC) model is employed to elaborate the correlation between plastic deformation mechanisms and texture evolution. The experimental results show that the types of textures are insensitive to the deformation temperature and strain rate, while the true strain dramatically affects the type of textures. The developed textures include {001}<100>, {012}<100> and η-fiber textures. In VPSC model, the bi-plane and pencil slip modes are selectively activated to match the experimental textures at different deformation strains. With an increase in strain, there is a gradual transition in the slip mode from bi-plane slip to pencil slip. The common textures in β phase of Ti alloys are strongly correlated with the active {112}<111> slip ({112} slip) and {123}<111> slip ({123} slip) modes. Additionally, to explain the effect of initial orientation on texture formation, various initial orientations in Ti alloys are employed in VPSC simulations. The results reveal that starting with a random orientation initially promotes the formation of {110}<111>, {001}<100> and η-fiber textures, accompanied by an increase in texture intensity as the strain level increases. Moreover, {110}<110> orientation undergoes rotation leading to develop {110}<111> texture with a decrease texture intensity, while {110}<112> orientation undergoes rotation inducing {110}<223> texture with an increased texture intensity. • Texture evolution of a near β-Ti alloy is investigated by hot compressive deformation experiments in β region. • A visco-plastic self-consistent model is developed to elaborate the correlation between plastic deformation mechanisms and texture evolution. • Texture types are insensitive to the deformation temperature and strain rate, while the true strain dramatically affects the type of textures. • The common textures in β phase of Ti alloys are strongly correlated with the active {112} and {123} slip modes. • Starting with a random orientation initially promotes the formation of {110}<111>, {001}<100> and η-fiber textures. [ABSTRACT FROM AUTHOR]

The flow behavior of a high‐strength Ti alloy (Ti‐55511) in the β region is studied by hot compressive experiments. A dislocation density–based constitutive equation, together with processing maps, is established to describe the flow behavior and hot workability of the studied Ti alloy. It is found that the strain rate (ε˙) and temperature (T) distinctly influence the hot compressive deformation behavior. The flow stress increases distinctly with a rising ε˙ or reducing T. The main softening mechanism in the β region is dynamic recovery (DRV). The established constitutive equation based on the work hardening (WH) and DRV mechanisms has the desired prediction accuracy, and the correlation coefficient between the predicted and experimental results is 0.9912. The processing maps indicate that a high strain rate (0.4–10 s−1) easily causes unstable deformation, whereas low and medium strain rates (0.001–0.2 s−1) are suitable for hot compressive deformation of the studied alloy. [ABSTRACT FROM AUTHOR]

Hot compression experiments of a Ti55511 titanium alloy are conducted to study the phase transformation characteristics and dynamic recrystallization (DRX) behavior. It is found that the fraction of α phase decreases with increasing the strain rate or deformation amount. Meanwhile, the original lamellar α phases easily transform into the spheroidal and bulk α phases at larger deformation amounts or higher strain rates. Most of α phases disappear and the final microstructures are mainly β phases when the temperature is over 800 °C. The DRX degree rises with raising the deformation amount or decreasing the strain rate. However, the DRX behavior becomes weaken with raising the deformation temperature. α phases are evenly distributed around β phases during hot compressive deformation, which not only restrains the growth of β phases but also promotes the DRX process of β phases. In addition, the geometric DRX takes place within α phases, while the continuous DRX occurs within β phases during the hot compression. Image 1 • Phase transformation and dynamic recrystallization (DRX) behavior of a Ti55511 titanium alloy are studied. • The volume fraction of α phase decreases with increasing the strain rate or deformation degree. • Initial lamellar α phases easily transforms into bulk/spheroidal α phases at the larger strains or higher strain rates. • The α phases not only restrains the growth of β phase, but also promotes the DRX process of β phase. • The geometric DRX takes place within α phases, while the continuous DRX occurs within β phases. [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 The isothermal tensile deformation behaviors of Ti - 5Al - 5Mo - 5V - 1Cr - 1 Fe alloy in β phase field are studied at the wide ranges of temperature and strain rate. The experimental results indicate that the processing parameters dramatically influence the isothermal tensile deformation characteristics of the studied alloy. Raising the deformation temperature or decreasing strain rate conspicuously decreases the flow stress. With the proceed of deformation process, the flow stress immediately approaches its peak value and then gradually decreases because of the dynamic softening induced by dynamic recrystallization and recovery. Meanwhile, the discontinuous yield phenomena can be found, especially at the higher deformation temperatures and lower strain rates. In the later tensile deformation stage, the flow stress sharply decreases due to the localized necking and microvoids coalescence, which leads to the final ductile fracture. A strain-compensated Arrhenius and Cingara constitutive equations are established to predict the tensile deformation characteristics of the studied alloy. A comparative study of the established constitutive equations is carried out, which reveals that the strain-compensated Arrhenius constitutive equation possesses the better capability to forecast the flow stress. Highlights • Isothermal tensile deformation behaviors of Ti-5Al-5Mo-5V-1Cr-1Fe alloy in β phase field are studied. • The early dynamic softening phenomena are induced by dynamic recrystallization and recovery. • Localized necking and microvoids coalescence lead to the final ductile fracture. • Strain-compensated Arrhenius constitutive equation possesses the better capability to forecast the flow stress. [ABSTRACT FROM AUTHOR]

In order to study the flow behaviors of an Al-Zn-Mg-Cu alloy at elevated temperatures, uniaxial tensile tests were carried out in wide deformation temperature and strain rate ranges. The flow stress rapidly increases to a peak value and then slightly decreases with the increased strain, and the dynamic recovery (DRV) is the primary softening mechanism. A unified constitutive model based on dislocation density was developed. An iterative procedure was implemented into the developed model to describe the flow behaviors at time-variant deformation conditions (e.g. the strain rate is changed during hot deformation). The predicted flow stresses were in accord with the experimental results, suggesting that the flow behaviors of the studied Al alloy at elevated temperatures can be well reproduced by the developed model. Meanwhile, the variations of the product of the instantaneous work hardening (WH) rate and stress caused by dislocation evolution, the dislocation density changing rate, as well as the dislocation mean free path, were given to analyze the WH and DRV mechanisms of Al-Zn-Mg-Cu alloy. [ABSTRACT FROM AUTHOR]

Dynamic recrystallization (DRX) behaviors of solution-treated Ni-based and aged superalloys under stepped strain rates were investigated by hot compressive tests and metallographic technique. The stepped strain rate means that the strain rate of specimen includes two stages, I and II. Moreover, the strain rate of stage I is larger than that of stage II for this study. The experimental results show that: (1) for the solution-treated Ni-based superalloy, the DRX fraction of deformed specimen at stepped strain rate is in between those of two specimens deformed at the constant strain rates of stages I and II; (2) however, for aged Ni-based superalloy, the DRX fraction of deformed specimen at stepped strain rate is larger those of two specimens deformed at the constant strain rates of stages I and II. It indicates that the stepped strain rate cannot accelerate the DRX behaviors of solution-treated Ni-based superalloy, but can accelerate the DRX behaviors of aged one. The reason is that the number of likely nucleation positions for the aged Ni-based superalloy is more than that for solution-treated one when the strain rate is abruptly decreased. The law can be applied in the hot working of the studied superalloy. [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]

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]

The dynamic recrystallization (DRX) behavior of a typical solution-treated Ni-based superalloy is investigated by hot compressive tests and metallographic observations. The DRX volume fractions of deformed specimens are evaluated based on optical micrographs. Results show that the DRX volume fraction and grain size increase with the increase of deformation temperature or the decrease of strain rate. It is found that the method to calculate the DRX volume fraction based on true stress–strain curves is not suitable for the studied superalloy. i.e., the relationships between the DRX volume fraction and strain are hard to obtain. It results in the lack of adequate experimental data to establish the DRX kinetics model by the conventional method. Therefore, a new method, in which only the DRX volume fractions in the center part of deformed specimens need to be employed, is proposed. Considering the friction-induced inhomogeneous deformation in specimens, the values of strain and strain rate in the center part of deformed specimens are obtained by finite element simulation. The material constants of DRX kinetics model are determined by the least square method. An agreement between the predicted and experimental results shows that the established model can well describe the DRX behavior of the studied superalloy. [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]

Two-stage creep-aging behavior of an Al–Cu–Mg alloy are studied by uniaxial tensile creep tests over wide ranges of temperature and external stress. Effects of creep-aging temperature and external stress on mechanical properties are discussed. It is found that the mechanical properties of the studied Al–Cu–Mg alloy are strongly sensitive to the creep-aging parameters. The two-stage creep-aging processing can change the characteristics of aging precipitates and dislocations, which greatly affects the mechanical properties of the studied Al–Cu–Mg alloy. With the increase of the second stage creep-aging temperature, the yield strength increases, while the ultimate tensile strength and elongation decrease. Meanwhile, the yield strength decreases with the increase of external stress. However, the ultimate tensile strength and elongation first increase and then decrease when the external stress is continuously increased within the tested conditions. Additionally, the mechanical properties of the two-stage creep-aged alloy are better than those of one-stage creep-aged and stress-free aged alloys. [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]

A detailed analysis of work-hardening behavior is useful to optimize the hot forming processing of metals or alloys. The hot compression tests of solution-treated and aged Ni-based superalloys are carried out over wide ranges of temperature and strain rate. Based on the experimental data, the effects of strain rate, deformation temperature, strain and δ phase (Ni 3 Nb) on the work-hardening behaviors are discussed in detail. The microstructures of the studied superalloy are observed to correlate with the complex dynamic deformation mechanisms. The experimental results show that the work-hardening behaviors of the studied superalloy are significantly affected by deformation temperature, strain rate, strain and δ phase. The work-hardening rate increases with the decrease of deformation temperature or the increase of strain rate. When the deformation degree is relatively small, δ phase can inhibit the dislocation movement and enhance the work-hardening behavior. However, with further straining, δ phase stimulates the occurrence of dynamic recrystallization and promotes the dynamic softening. When the deformation temperature is higher than the dissolution temperature of δ phase, the effects of δ phase on work-hardening behaviors are weakened. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hot tensile deformation and fracture behavior of a typical Al–Zn–Mg–Cu alloy were studied. [•] The elongation to fracture is affected by the coupled effects of deformation temperature and strain rate. [•] The main deformation mechanism is the lattice diffusion controlled dislocation climbing. [•] Microvoids coalescence is the main fracture mechanism under relatively low temperatures. [•] The established Arrhenius-type constitutive model can accurately predict the peak stress. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hot tensile deformation and fracture behavior of 42CrMo steel were studied. [•] Localized necking is dominant under strain rate range of 0.1–0.001s−1. [•] The gage segments of specimens maintain the uniform macroscopic deformation under 0.0001s−1. [•] The elongation to fracture is affected by the coupled effects of deformation temperature and strain rate. [ABSTRACT FROM AUTHOR]

Abstract: The hot tensile deformation and fracture behaviors of the hot-rolled AZ31 magnesium alloy were studied by uniaxial tensile tests with the temperature range of 523–723K and strain rate range of 0.05–0.0005s−1. Effects of deformation parameters on the strain hardening rate, strain rate sensitivity, microstructural evolution and fracture morphology were discussed. The results show that: (1) The flow curves show a considerable strain hardening stage and no obvious diffuse necking stage under the relatively low temperatures (523 and 573K). (2) The elongation to fracture increases with the increase of the deformation temperature. But, the sharp drop of the elongation to fracture under 723K and 0.0005s−1 results from the synthetical effects of the grain growth, inverse eutectic melting reaction (α + β = L) and the incipient melting of α matrix. (3) For the case with the deformation temperature of 623K and relatively low strain rates, the fracture mechanism is the combination of the void coalescence and intergranular fracture. (4) Under the deformation temperature of 723K, the fine recrystallized grains experienced a rapid growth and the deformation mechanism is the dislocation creep with the help of inverse eutectic liquid phase. (5) The presence of proper amount of liquid phase on the grain boundary changes the deformation mechanisms, and makes great contribution to the high ductility. However, it will deteriorate the material ductility if the amount of liquid phase is too much. [Copyright &y& Elsevier]

The flow characteristics and microstructure evolution of an aged nickel-based superalloy are researched by thermal compression experiments at different temperatures (1223–1283 K) and strain rates (0.001–0.1 s−1). Based on the theoretical analysis, the dynamic recrystallization kinetics and the evolution of grain size are quantitatively modeled. A unified dislocation density-based model is developed to characterize the flow features of the researched superalloy. In the developed model, the work hardening effect is taken into account by involving the coupled effects between the dislocations and substructures/grain boundaries/δ phases. Especially, the initial contents/morphologies of δ phase are reasonably considered. The dynamic softening mechanisms including dynamic recrystallization and dynamic recovery are considered. The comparisons between the predicted and experimental data indicate that the developed unified model can make accurate predictions for the flow stresses of the aged nickel-based superalloy at constant or variable strain rates. Also, it is found that the morphology of δ phase gradually transforms from spherical to short-rod-like or needle-like with the increased aging time. The dissolution and bend of δ phase induced by dislocation movement easily occur. Besides, the DRX behavior is accelerated, and the grains are refined as the aging time is increased. • Flow characteristics and microstructure evolution of an aged nickel-based superalloy are researched. • A unified dislocation density-based model is developed to describe the flow features of the studied alloy. • The coupled effects between the dislocations and substructures/grain boundaries/δ phases are considered. • The δ phase gradually transforms from spherical to short-rod-like or needle-like with increasing aging time. • The dissolution and bend of δ phase induced by dislocation movement usually occur. [ABSTRACT FROM AUTHOR]

High-temperature deformation features of the Ni-Mo-Cr-based superalloy with the pre-precipitation μ phase are researched utilizing thermal compression experiments. For unravelling the nucleating characteristics of substructures and interacted with μ phase in hot deformation, the transmission electron microscope (TEM) is utilized. Electron backscatter diffraction (EBSD) is employed to explore the nucleating/growth mechanisms of dynamic recrystallization (DRX). An improved physically-mechanism (IPM) model is set up for reconstituting flow stresses and microstructural evolution. The investigated results demonstrate that high-density subgrains/dislocation loops can be mainly formed by dislocations entanglement and the pinned mechanism of μ phase/grain boundaries. In addition to discontinuous/continuous DRX nucleating mechanisms, the nucleating mode induced by twins and the stimulated nucleus by μ phase are also detected. The coarsen of DRX grains is substantially repressed with reducing compressed temperature or ascending strain rate, which exacerbates the inhomogeneous scatter of grains. Meanwhile, the contents of low angle grain boundaries (LAGBs) sensibly increase, owing to the sharply increase of substructures. The superior consistence of reproducing and tested results suggests the IPM model can be employed to exactly forecast the stresses, grain size as well as DRX fraction of the investigated Ni-Mo-Cr-based superalloy with the pre-precipitation μ phase. • Hot deforming characteristics of a Ni-Mo-Cr-based superalloy with the pre-precipitation μ phase are investigated. • The pre-precipitation µ phase can significantly stimulate DRX grains nucleation and inhibit the coarsening of DRX grains. • The DRX nucleating mechanisms of continuous DRX, discontinuous DRX and twinning stimulated DRX are activated. • The proposed improved physically-mechanism constitutive model can precisely forecast flow stresses and microstructure. [ABSTRACT FROM AUTHOR]

• The microstructure evolution of a hot deformed Ti-55511 alloy is studied. • A unified constitutive equation is established to model the flow behaviors and microstructure evolution. • The discontinues and geometric DRX mechanisms are dominant. • Increasing the deformation temperature can increase the DRX fraction and sub-grain size. • The chain-like small DRX grains and the flow location occur at high strain rates. The microstructure evolution of a Ti-55511 alloy deformed at high temperatures (from 1163 K to 1253 K) and wide strain rate range (from 10 s−1 to 0.001 s−1) is studied by isothermal compression tests. Based on the sensitivity of dislocation density to deformation conditions, a unified constitutive equation is established to describe the evolution of flow stress, grain size and dynamic recrystallization (DRX) fraction. The results show that the initial grain boundaries are serrated, and the sub-grains and DRX grains are formed with the further deformation. Furthermore, the discontinuous and geometric DRX mechanisms are dominant recrystallization mechanism. Increasing the deformation temperature can increase the DRX fraction and sub-grain size. However, the abnormal growth of β grains occurs at 1253 K. The DRX fraction decreases with the increased strain rate. Meanwhile, the chain-like small DRX grains and the flow localization occur at high strain rates. Also, the established constitutive model is verified by the experimental results, and the correlation coefficient is 0.9929, indicating the excellent prediction ability of the established constitutive model. [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 compression features of Ti-55511 alloy are investigated by high-temperature compression tests in α+β region. It is found that the flow stress and softening mechanisms are obviously influenced by deformation conditions. The true stress decreases with the reduced strain rate or the raised temperature. The spheroidization of α phase and dynamic recrystallization (DRX) of β phase easily occur at low temperatures such as 973, 1003 and 1033 K, while the dynamic recovery (DRV) of β phase mainly occurs at high temperatures such as 1063 K because of the transformation from α phase to β phase at relatively high temperatures A dislocation density-based constitutive model, which is associated with DRV, work hardening mechanisms and the spheroidization of α phases, is established and validated to describe flow behavior. The correlation coefficient (R) and average absolute relative error (AARE) of the established model are 0.9924 and 6.8%, respectively. 3D power dissipation efficiency maps and processing maps are established to determine the appropriate processing window, i.e., too low temperatures (lower than 973 K) or too high strain rates (higher than 1 s−1) easily induce flow instability. Therefore, the medium temperature (1003–1063 K) and the low strain rate (0.001–0.1 s−1) are applicable for thermal compression of the studied titanium alloy. • Hot compression features of Ti-55511 alloy is investigated by high-temperature compression tests in α+β region. • DRX easily occurs at low temperatures, while DRV mainly occurs at high temperatures. • A accurate dislocation density-based constitutive model considering the spheroidization of α phases is established. • The optimal forming temperature and strain rate are 1003–1063 K and 0.001–0.1 s−1. [ABSTRACT FROM AUTHOR]

Deformation behavior and precipitation features of an Al–Cu alloy are investigated using uniaxial tensile tests at intermediate temperatures. It is found that the true stress drops with the decreased strain rate or the increased deformation temperature. The number of substructures and the degree of grain elongation decrease with the raised temperature or the decreased strain rate. At high temperatures or low strain rates, some dynamic recrystallized grains can be found. The type of precipitates is influenced by the heating process before hot tensile deformation. The content and size of precipitates increase during tensile deformation at intermediate temperatures. As the temperature increases over 200 °C, the precipitation process (Guinier Preston zone (G.P. zones)→θ′′ phase→θ′ phase) is enhanced, resulting in increased contents of θ′′ and θ′ phases. However, θ′′ and θ′ phases prefer to precipitate along the {020}Al direction, resulting in an uneven distribution of phases. Considering the flow softening degree and the excessive heterogeneous precipitation of θ′′ and θ′ phases during hot deformation, the reasonable strain rate and temperature are about 0.0003 s−1 and 150 °C, respectively. [ABSTRACT FROM AUTHOR]

Spheroidization and dynamic recrystallization (DRX) mechanisms of a Ti-55511 alloy during hot compression in α+β region is investigated. It is found that the spheroidization of lamellar α phases and DRX of β phases, which are obviously influenced by deformation conditions, are the main softening mechanisms. The spheroidization fraction of lamellar α phases first increases with the raised temperature or strain rate. However, the spheroidization fraction of lamellar α phases begins to drop at about 700 °C as the strain rate is higher than 0.01 s−1, and the maximum spheroidization fraction of lamellar α phase is about 2.3%. This phenomenon is attributed to the Implanting-Mechanism, which is induced by the common or close orientation relationships of the spheroidized and equiaxed α phases, as well as few dislocations between the spheroidized and equiaxed α phases. Contrarily, the lamellar α phases are obstructed from equiaxed α phases by a mass of dislocations. Additionally, the DRX degree of β phases increases with the reduced temperature or the raised strain rate. • Spheroidization and DRX mechanisms of a Ti-55511 alloy during hot compression in α+β region is investigated. • Spheroidization fraction of lamellar α phase first increases then drops with the raised strain rate. • The maximum spheroidization fraction of lamellar α phase is about 2.3% near 700 °C and 0.01 s−1. • Implanting-Mechanism, induced by the close orientation relationships of spheroidized and equiaxed α phases, is proposed. • The DRX extent of β phases increases with the reduced temperature and raised strain rate. [ABSTRACT FROM AUTHOR]

The uniaxial tensile tests are performed to study flow behavior of a nickel-based superalloy with different initial microstructures at an intermediate temperature range (473–973 K). The experimental results show that the obvious serrated flow characteristics can be observed from the flow stress curves. Meanwhile, it is concluded that the occurrence of serrated flow features not only associate with deformation parameters, but also are prominently influenced by different initial microstructures. Furthermore, based on the plastic deformation mechanism of the investigated superalloy and dislocation-solute atoms dynamic interactions, a physically-based constitutive model is developed. The dynamic characteristics of the developed model are discussed, i.e., the evolution of moving dislocation, solute atoms concentration, and the strain rate dependent stress are analyzed. Additionally, various types of serrations are numerically simulated by appropriate parameters. Also, the predicted results show a good coincident with the observed data, suggesting that the established model can accurately describe the intermediate-temperature flow behaviors involving the serrated flow features of the investigated nickel-based superalloy. Unlabelled Image • Serrated flow features of a nickel-based superalloy with different initial microstructures were study. • Serrated flow features are prominently influenced by deformation parameters and initial microstructures. • A physically-based constitutive model is developed considering dislocation-solute atoms dynamic interactions. • The evolution of moving dislocation, solute atoms concentration, and the strain rate dependent stress are analyzed. • The established model can well described the intermediate-temperature the serrated flow features. [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]

The metadynamic recrystallization (MDRX) characteristics of a Ni-Cr-Mo alloy are investigated using the double-pass thermal compression tests. The impacts of double-pass compression parameters on the kinetic features and microstructural changes are clarified. Results signify that the MDRX softening behaviors are remarkably accelerated with increasing of compression temperature, first-pass strain or strain rate. The bulging of the MDRX grain boundary and the annihilation/interaction of substructures become weaken at low compression temperature or small first-pass strain, enhancing the grain refining during MDRX. However, the MDRX grains coarsen rapidly with decrease of strain rate. Based on the comprehensive impact of double-pass compression parameters on softening fraction and grain size, the MDRX kinetic model and MDRX grain size model are developed. The predicted results are well matched the experimental data, which suggests that the established models can precisely characterize the changes of softening characteristics and grain size of the researched alloy during MDRX. • The kinetic behaviors and microstructural evolution of a Ni-Cr-Mo alloy during MDRX are revealed. • Softening behavior caused by MDRX are prominently affected by the evolution of substructures and MDRX grains. • The annihilation/interaction of substructures exert a significant influence on the bulging and serrated behaviors of MDRX grain boundary. • The proposed kinetic equation and grain size model can precisely forecast the variation of softening fraction and grain structure during MDRX. [ABSTRACT FROM AUTHOR]

The flow characteristics of a Ni-Mo-Cr base alloy are researched by the double-stages hot compression with step-strain rates. Electron backscatter diffraction (EBSD) as well as transmission electron microscopy (TEM) are adopted to systematically comprehend the influences of compressed parameters on microstructural changes. To forecast the hot compressed behaviors, a physically-based constitutive model with considering the evolution characteristics of dislocation density, subgrain and the grain structure is developed. Experimental results indicate that the elevated compressed temperature can exacerbate the dislocation consumption, subgrain rotation/interaction and dynamic recrystallization (DRX) grains coarsening. However, the prominent dislocation accumulation, subgrain generation and the refinement of DRX grains come up as the strain rates at the first or second stage of hot compression are ascended. The discontinuous DRX characterized by the bulging/serrated of grain boundaries is the major DRX nucleation mechanism of the researched alloy. The forecasted compressed stress, grain size and DRX fraction well match the tested results, which indicates the constructed physically-based constitutive equations can be employed to model the high-temperature features and microstructural changes of the studied Ni-Mo-Cr base alloy in double-stages hot compression with step-strain rates. • The flow characteristics of a Ni-Mo-Cr base alloy in double-stages hot compression with step-strain rates are revealed. • With increasing strain of first stage, high density substructures are formed and the bulging of DRX grain boundary is inhibited. • The consumption of substructures and coarsening of DRX grains are enhanced with raising of compressed temperature. • The major DRX nucleation mechanism of the researched alloy in double-stages hot compression with step-strain rates is DDRX. • The developed physically-based constitutive model can precisely reproduce the flow behaviors and microstructural changes. [ABSTRACT FROM AUTHOR]

Isothermal compression tests, electron backscatter diffraction (EBSD) observations and quantitative analysis were performed to investigate high-temperature deformation behavior and recrystallization mechanism of Ti-55511 alloy in β phase region. The stress-strain curves, calculated activation energy and microstructure characterization show that dynamic recovery (DRV) and dynamic recrystallization (DRX) are the main soften mechanisms. DRX becomes more significant with decreasing strain rate and increasing deformation temperature and true strain. Recrystallization grains are identified by calculated grain orientation spread (GOS). It is found that quantitative microstructural characteristics, such as DRX volume fraction and DRX grain size, are strongly dependent on process parameters. The discontinuous dynamic recrystallization (DDRX) by grain boundaries bulging and continuous dynamic recrystallization (CDRX) by progressive sub-grains rotation are observed in the deformed microstructure of Ti55511 alloy. The flow softening rate and kinetics exponent of DDRX are higher than those of CDRX. With increasing deformation temperature, DRX mechanism has transformed from DDRX to CDRX, resulting in the unexpected decrease of DRX kinetics exponent n D and flow softening rate. The η bcc fiber, ε bcc fiber and ξ bcc fiber are the dominant texture component in deformed Ti–55511 alloy. The weakening of the deformation texture is accompanied by the occurrence of DRX, which can be attributed to the random orientation distribution of DRX grains. • DRX grains were identified by calculated GOS, and the effect of deformation parameters on DRX was quantitatively analyzed. • The DDRX by grain boundaries bulging and CDRX by progressive sub-grains rotation were comparative investigated. • With increasing temperature, DRX mechanism has transformed, and DRX kinetics exponent and flow softening rate decrease. • The weakening of deformation texture is accompanied by the occurrence of DRX. [ABSTRACT FROM AUTHOR]