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The thermo-mechanical processing (TMP) behavior of nickel-based superalloys during hot working exhibits highly non-linear and complex characteristics, necessitating an understanding of deformation mechanisms for industrial applications. In this study, we developed an autoencoder-prediction network (AE-PN) to model the TMP behavior of the Inconel 718 superalloy in an unsupervised way within the temperature range of 900–1200 °C and strain rates of 0.001–10 s−1. The AE-PN effectively reduces the dimensionality of stress-strain curves in a non-linear manner while preserving critical flow features, enabling accurate reconstruction of stress-strain curves. The AE-PN established strong correlations between processing parameters and the latent space, achieving high reconstruction accuracy for continuous flow curves (testing RMSE = 4.19). Latent features derived from stress-strain curves were linked to key characteristics of hot deformation behavior, including peak stress, strain hardening, and flow softening. Notably, one major latent component was strongly correlated with peak stress (R2 = 0.9971), highlighting its role as a physics-related variable connected to TMP behavior. For additional datasets within the processing window, the AE outperformed a conventional artificial neural network (ANN) model, achieving an RMSE of 7.98 compared to the ANN's RMSE of 60. Furthermore, hot workability characteristics, such as flow softening and dynamic recrystallization (DRX), were systematically analyzed using a processing map and microstructural analysis. This AE-PN framework provides interpretable insights beyond traditional ‘black-box’ systems, offering accurate stress-strain curve predictions and deeper interpretation of processing parameters through latent space exploration.

The microstructure evolution of aluminum alloys during plastic deformation is a complex metallurgical process controlled by interacting physical mechanisms, such as recovery, continuous dynamic recrystallization (CDRX), and substructure evolution. The present study proposes a dislocation-based model framework to describe the microstructural evolution of dislocation density, subgrain size, misorientation angle, and flow stress. The wall dislocation density is modeled on the basis of the average subgrain size and misorientation evolution. The dislocation density and substructure evolution are independently simulated and compared with electron backscatter diffraction (EBSD) experimental results. Their mechanisms are thoroughly discussed. The decrease in low-angle subgrain size and the increase in the misorientation angle of subgrain boundaries with increasing strain rate, as well as their evolution with temperature and strain rate, are well reproduced over a wide range of large strains. Furthermore, the evolution of these experimental substructures is employed to model other related mechanical properties. The framework is successfully applied and validated for AA1050 and AA5052 aluminum alloys across different deformation conditions.

The stress-strain curves and dynamic recrystallization (DRX) behavior of high carbon low alloy (HCLA) steels were investigated by hot deformation at a wide range of temperatures (900–1150 °C) and strain rates (0.01–10 s−1). Based on the dislocation density theory, this paper established the stress-strain curve equation and analyzed in detail the critical stresses for nucleation and growth of DRX in relation to the stress-strain curve. The main DRX mechanism of the HCLA steel is discontinuous dynamic recrystallization (dDRX). When deformed at high strain rates, the DRX grains nucleated non-uniformly, preferentially at the trigonal grain boundaries. Conversely, at low strain rates, both serrated and bulged grain boundaries can simultaneously be the nucleation sites of DRX grains in a uniform manner. In the DRX type curve, when the strain rate reduced from 0.1 s−1 to 0.01 s−1, the inoculation temperature for the rapid growth of DRX grains in HCLA steel was reduced from 1050 °C to 1000 °C. Compared to the initial microstructure, the average grain size at 1050 oC-0.1 s−1 decreased by 79.4%, while the aspect ratio of the grain shape increased by only 9.1%. Considering the variation of temperature and strain rate in industrial production, the optimal deformation parameters of the HCLA steel to obtain the equiaxial DRX grains are the deformation temperature of 1000–1050 °C, and the strain rate of 0.1–1 s−1.

The Mg-8Gd-3.5Y-1.5Zn-0.8Mn (wt%) alloy was designed and prepared to investigate the synergistic dynamic recrystallization (DRX) mechanism at high temperature and low strain rate. We studied DRX process at different strain rates and temperatures, and revealed the corresponding mechanisms. The results show that at a low strain rate of 0.01 s−1 and 723 K, the grain size significantly decreases compared to 623 K, the grain boundaries protrude outward, and new small grains are generated. Quantitative calculations indicate that the thermal deformation mechanism can be reflected by the dissipation efficiency factor η. As the value of η increases, the dynamic softening mechanism shifts from dynamic recovery (DRV) to DRX. When the value of η is greater than 0.36, under these conditions, continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) occur. This is because dislocation slip is hindered at grain boundaries, leading to dislocation entanglement and rearrangement, promoting the formation of low angle grain boundaries (LAGBs). As the deformation process progresses, the dislocation density of LAGBs continues to increase, reaching the critical point of promoting DRX. On the one hand, the high dislocation density region can serve as a nucleation site for DRX, and on the other hand, its characteristic of high strain storage energy is the driving force for CDRX nucleation. With the occurrence of CDRX, LAGBs gradually transform into high angle grain boundaries (HAGBs). CDRX provides nucleation sites for DDRX, and the outward protruding grain boundaries promote dynamic recrystallization nucleation. The distortion energy difference between the new grains and the surrounding matrix promotes the continuous movement of LAGBs, ultimately leading to the growth of crystal nuclei and the formation of recrystallized grains. The results indicate that controlling the hot working conditions can improve the microstructure of the alloy through recrystallization, thereby developing high-strength magnesium alloys.

The mixed dynamic recrystallization of titanium alloys during hot deformation is rarely described in the existing microstructure evolution models and constitutive models. In this paper, the mechanism of mixed dynamic recrystallization of a near-α titanium alloy rolled sheet during hot tension was analyzed. The used TA15 rolled sheet is mainly composed of equiaxed grains with a lot of deformed structure, which promotes dynamic recrystallization during hot deformation. Continuous dynamic recrystallization is the predominant mechanism of microstructure evolution in the deformation region with the ln Z of about 47.5 and true strain of about 0.3. With the decrease of parameter Z, discontinuous dynamic recrystallization is enhanced. Then a physically-based constitutive model was developed, considering subgrain rotation, recrystallization nucleation, recrystallization grain growth, recrystallization grain transformation into deformation structure and microvoids evolution. The model can well describe the two kinds of mixed dynamic recrystallization: continuous dynamic recrystallization and discontinuous dynamic recrystallization occur successively and simultaneously. Based on the developed model, the process window of hot forming for TA15 titanium alloy components is established, realizing grain size reduction of 20 % and no necking.

The hot deformation and fracture behavior of TC4 with and without diffusion bonding (DB) are investigated in both experimental and numerical methods in this study. The hot tensile tests of TC4 specimens with and without DB have been carried out at a temperature of 750 °C and strain rate of 0.1–0.0001 s−1, and the corresponding microstructure and fracture morphology under different deformation conditions have been analyzed by scanning electron microscope (SEM) and electron back scatter diffraction (EBSD). Straight grain boundaries, fine dynamic recrystallization (DRX) grains and weak joints formed by the DB process, which lead to lower stress and fracture strain than those of base metal (BM) specimens. Based on the experimental results, a new unified constitutive model considering the weld-dependent fracture coefficients and internal variables is developed, which can accurately predict the hot deformation and fracture behavior of TC4 with and without DB, describing the influence behavior of DB interface on hot deformation, as well as the evolutions of internal variables, including dislocation density, reserve fraction, DRX fraction and damage. The constitutive model has been further applied to the finite element method (FEM), and the prediction ability of the deformation behavior and the fracture of the model for hot deformation processes have been verified. It provides a theoretical basis for further accurate simulation of the hot forming of titanium alloy with DB.

In this study, the microstructure evolution on hot deformation was investigated and a dynamic recrystallization (DRX) kinetic model was constructed based on the hot deformation behavior of the homogenized state Mg–7Gd–3Y–1Zn–0.5Zr (VW73B) alloy within 713–773 K and 0.01–0.1 s−1. The DRX critical strain reduced when the deformation temperature (T) increased and increased when the strain rate (ε˙) increased. The variation trend of the DRX volume fraction was inversely proportional to the critical DRX strain. The constructed DRX kinetic model was modified by introducing a compensation factor; the modified model showed a mean absolute deviation of the DRX volume fraction of 1.8%. Combined with the microstructure analysis, it can be found that the Long Period Stacking Ordered (LPSO) phase is able to promote DRX during the hot deformation, but its ability to promote DRX is less pronounced than that of grain boundaries. At the block-shaped LPSO phase interface, the grain boundary arched by strain induction provided a nucleation site for DRX, enabling discontinuous dynamic recrystallization (DDRX). At the lamellar LPSO phase interface, continuous dynamic recrystallization (CDRX) occurred predominantly through the continuous migration and merging of subgrains, resulting in the formation of DRX grains. The results of this study could guide future research on the DRX of the VW73B alloys with varied applications.

In this work, the flow behaviors and microstructure evolution of a solid solution Ti55511 alloy deformed in the two-phase region are investigated by hot compression experiments. Subsequently, The spheroidization mechanisms of α phases and the refinement mechanism of β matrix are analyzed. The alloy exhibits obvious work hardening (WH) and flow softening characteristics. The secondary α phases gradually precipitate and spheroidize, while the primary α phases dissolute above the solution temperature or coarsen when the alloy is deformed below the solution temperature. Meanwhile, the β matrix undergoes continuous dynamic recrystallization (CDRX) behavior. The increase of deformation amounts promotes the simultaneous precipitation and spheroidization of lamellar α phases. Raising deformation temperature inhibits the precipitation and spheroidization of lamellar α phases. However, the maximum values of precipitated and spheroidized lamellar α phase occur at 0.01 s−1. Higher strain rate can promote CDRX of β matrix between 1003 and 1033 K, but inhibit it between 1063 and 1123 K, indicating differences in the dynamic recrystallization (DRX) mechanism at different temperature regions. A unified constitutive model based on physical mechanisms is proposed. The model takes into account both WH and grain boundary strengthening effects by coupling all parts of phases. Furthermore, the dynamic softening, including dynamic recovery (DRV), spheroidization of lamellar α phases, and CDRX of the β matrix, are also considered. Material constants are determined using a genetic algorithm (GA), and the experimental data align well with the predicted data. Finally, process parameters are optimized based on the model to achieve favorable microstructures.

Tungsten wire with high strength and toughness for silicon wafer cutting in photovoltaic industry is a new hot research content. In order to improve the strength and processing performance of tungsten wire, tungsten alloy containing 0.5 wt%La2O3 was prepared by powder metallurgy method. The hot deformation behavior and microstructure evolution of tungsten lanthanum alloy were studied. Studies have shown that the alloy is extruded to grow fine grains, and its texture structure mainly presents two directions. The grain size of the instability zone is too large, and there are obvious cracks. With the decrease of strain rate and the increase of temperature, the recrystallization ratio of the alloy increases gradually, showing a partial equiaxed grain structure. The recrystallization ratio reaches the maximum at 1600 °C/0.01s−1, but it is still not completely recrystallized. Lanthanum oxide gradually aggregates to the grain boundary during the hot deformation process, which improves the thermal deformation activation energy of tungsten. The Q value is about 410.018 kJ/mol, which improves the high temperature strength of tungsten alloy. The compressive strength of tungsten alloy at high temperature is about 10% higher than that of pure tungsten. Combined with the hot processing map, the optimum process parameters of tungsten alloy were determined to be 1400 °C–1600 °C, 0.01–0.05s−1. The φ35.5 μm ultra-fine tungsten wire was prepared according to this parameter. The microstructure of tungsten wire is uniform and dense, and there are no cracks and defects. The tensile strength of tungsten wire is extremely high, reaching 5723 MPa.

This study investigates the hot deformation behavior, microstructural evolution, and processing map of a high-carbon high-strength low alloy steel subjected to hot compression tests in the temperature range of 850 °C–1150 °C and strain rates from 0.01 s⁻1–10 s⁻1. A highly accurate flow stress constitutive equation has been established and the activation energy of the experiment steel is 462.6 kJ/mol. Processing maps were generated to identify unstable zones, low-power dissipation zones, and optimum processing zones, accompanied by detailed discussions on corresponding microstructures and mechanical properties. The recommended hot deformation parameters at a true strain of 0.9 are temperatures from 944 °C to 1050 °C and strain rates from 0.01 s⁻1 to 0.52 s⁻1 according to the processing map. The effects of deformation temperature and strain rate on the microstructure were then investigated. It is revealed that reducing deformation temperature and increasing strain suppress the recrystallization process and the growth of recrystallized grains; while VC precipitation is suppressed under high temperatures and high strain rates.

The dynamic recrystallization (DRX) behavior and microstructure evolution of a novel Al-Zn-Mg-Cu-Zr alloy was investigated by isothermal compression tests at temperature of 350–470 °C and strain rate of 0.0001–1 s−1. The results showed that the flow behavior revealed typical dynamic recovery (DRV) characteristics at a high strain rate (1 s−1), while exhibited a DRX shape when the strain rate decreased. The critical strains (εc) of the DRX decreased with the decrease of strain rate or the increase of deformation temperature. A low temperature was conductive to precipitation behavior, the coarse precipitates and dispersed Al3Zr particles would pin the dislocations and substructures, which inhibit the DRX process. The DRX mechanism of the Al-Zn-Mg-Cu-Zr alloy was dominated by continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) during the hot deformation process, upon increasing the temperature and decreasing the strain rate, there was a transition point of DRX mechanism from DDRX to CDRX. Moreover, the linear relationship between the Zener-Hollomon (Z) parameter and DRX grain size was established for the further exploration of the transition of the dominant DRX mechanism.

The workability of rare earth magnesium alloys is deteriorated due to work hardening after extrusion deformation, significantly impacting their application in the automotive and aerospace industries. In this study, the effects of various hot working parameters on the microstructure and hardness of an extruded Mg–1Al-1.5Nd-1.5Y-0.5Gd alloy were investigated including strain rate ranging from 0.001 s⁻1 to 1 s⁻1 and deformation temperature between 300 °C and 450 °C. The results indicate that the average grain size of the hot compressed alloy was significantly refined to only 3.59 μm under the strain rate of 0.01 s⁻1 and the deformation temperature of 400 °C, representing a 36% reduction of average grain size compared to as-extruded alloy. Additionally, the Vickers hardness of hot compressed alloy was improved to 58.5 HV, indicating a 31% increase of hardness relative to the specimens at extruded condition. During thermal deformation, recrystallization was induced by the Al₂Nd phase, while nucleation was stimulated by the Al₂RE (Y, Nd, Gd) phase to promote recrystallization. Below 350 °C, the nucleation effect of Al₂RE particles served as the primary driving force for dynamic recrystallization (DRX). However, as temperature increases, the refinement of grains was progressively dominated by the Al₂Nd phase through the induction of dislocation walls. The different impacts of various second phases on DRX behavior were underscored. At 400 °C, the critical temperature for the formation of dislocation walls and the transformation of substructures, a fine-grained microstructure with a high dislocation density was exhibited by the hot-worked alloy, resulting in enhanced hardness.

Mg alloys are the lightest metallic structural material with tremendous application value. Dynamic recrystallization (DRX) is the most important grain refining and texture weakening mechanism for Mg alloys. The DRX kinetic models establish the relationship between the DRX fraction and the deformation parameters. It can effectively guide the determination of the deformation parameters to control the microstructure and the mechanical properties of the Mg alloys. In this study, the high-temperature flow behavior and DRX characteristics of Mg alloys are comprehensively reviewed. Additionally, the DRX kinetic models for the AZ, ZK and rare earth (RE)-containing series Mg alloys are systematically evaluated. Recommendations are provided regarding the appropriate selection of the DRX kinetic models for various Mg alloys. Lastly, the limitations of the existing DRX kinetic models are critically discussed and potential directions for future research and applications are outlined.

Through hot compression and subsequent heat treatment experiments on GH4079 superalloy, the influence of different hot deformation and heat treatment conditions on the evolution of GH4079 superalloy microstructure was studied. The evolution of grains and γ′ phases under different thermomechanical conditions was investigated. The results indicate that at deformation temperatures above 1100 °C and strain rates ranging from 0.01 to 0.1 s−1, the primary mechanism of dynamic softening in the alloy is discontinuous dynamic recrystallization (DDRX). When the deformation temperature is below 1100 °C and strain rates range from 0.01 to 0.1 s−1, both continuous dynamic recrystallization (CDRX) and DDRX are the main dynamic softening mechanisms. Due to high strain energy accumulation, the samples deformed at lower temperatures (below 1100 °C) and then solution-treated at 1120 °C for 8 h exhibit significant increases in recrystallization volume fraction and recrystallization grain size. Conversely, the samples deformed at higher temperatures (above 1100 °C) and then solution-treated at 1120 °C for 8 h show minimal changes in recrystallization volume fraction and recrystallization grain size. After solution treatment at 1140 °C, the grain size of the alloy significantly increases. The samples deformed at higher strain rates exhibit the evolution of fine γ′ phases into elongated rod shapes during solution treatment, while larger γ′ phases undergo splitting processes.

Hot compression tests were used to examine the hot deformation behavior and of high-grade pipeline X80 steel at strain rates of 0.001–1 s−1 and temperatures of 950–1100 °C. Two approaches were used to model material flow curves. The first used the Zener-Hollomon parameter, Z, to show the impact of deformation temperature and strain rate on flow stress, using the Arrhenius constitutive equation. The second used a rule of mixture to represent the material's flow curve, considering work hardening and dynamic recrystallization flow stresses. The first method was accurate at low Z and low strains, while the second method accurately displayed peak stress, was suitable for large strains, and predicting flow curves at industrial strain rates. The microstructure of X80 steel exhibits strain rate dependence under hot deformation conditions, with finer and more equiaxed microstructures observed at higher strain rates. These findings align with processing map predictions for stable deformation behavior, suggesting potential for optimized hot working processes. The static recrystallization kinetics showed that the Avarmi exponent, n, ranges from 1 to 2 for strains of 0.2 and 0.35 at 950 °C, but higher values were observed under hot deformation conditions.

In this study, the thermal deformation behavior of Cu–Ti–Zr(-Mg) alloys were investigated by Gleeble-1500D. The two alloys were deformed at 700–900 °C with 0.003–10 s−1 strain rate. The intrinsic equations of the two alloys were constructed and calculated thermal activation energies, which indicates that it is improved from 325.67 kJ/mol to 344.03 kJ/mol after Mg addition. The result showed that the hot working area of Cu–Ti–Zr alloy is greatly extended after Mg addition, and rheological instability area is reduced. The morphology of the alloys was observed to analyze thermal behavior. It revealed that Mg elements inhibited the occurrence of dynamic recrystallization and shifted the texture types in the alloys by characterization of EBSD. TEM results showed that the phases during hot deformation in Cu–Ti–Zr–Mg are Cu4Ti and Cu10Zr7, which are in a semi-coherent relationship with the Cu matrix.

Ultrahigh-strength titanium alloy (≥1250 MPa) innovation calls for an integrated framework combining novel deformation processing and microstructural control. However, a confluence of constitutive model and the deformation behavior of a new β-metastable titanium alloys (Ti-4Al-4Mo-4 V-5Cr-2Zr-1Nb, Ti-1500G) remained ambiguous, making the optimization of precise processing parameters is difficult clarified. An integrated response of the flow stress caused by multiple mechanisms initiated softening and work hardening was characterized using a strain-compensated constitutive model, including shear bands, dynamic recovery and dynamic recrystallization (DRX). Particular attention in this work was placed on in-depth understanding the thermal processing sensitivity of deformation mechanisms transformation. A two-dimensional deformation-mechanism map (DMM) as a function of temperature and strain rate was creatively proposed on the basis of energy dissipation efficiency mechanisms. The transition of deformation mechanisms was attributed to the decreasing thermal activation energy from α + β phase region (413.78 kJ/mol) to β phase region (219.24 kJ/mol), accompanied by dynamic phase transformation and activated dynamic α globularization. Otherwise, low strain rates promote α phases-dislocation interactions to accelerate the DRX grains nucleation. The DMM with various physical parameters is an efficient approach for guiding the thermomechanical processing of ultrahigh-strength titanium alloy large-scale components to reduce cracking tendency.

Refining the second phase is an effective approach to enhancing the strength and toughness of metallic materials. This paper adopts a novel composite thermomechanical processing technique (pre-annealing, semi-solid isothermal treatment, and post double extrusion) to fabricate a high strength-ductility Al-4.5 wt% Cu binary alloy via the spheroidization and nano-crystallization of the primary phase (Al2Cu). The resulting room-temperature tensile strength, yield strength, and elongation reached 450 MPa, 339 MPa, and 17.3 %. The combined effects of dual nanoparticle (i.e. broken nanoparticles and precipitated nanoparticles) strengthening and grain boundary strengthening are identified as the direct reasons for the enhanced strength. The uniformly alternated coarse and fine grain regions in the bimodal grain structure can coordinate deformation, and the dispersed spherical phase can weaken stress concentration, which are important factors for high plasticity. This work offers new insights for developing high-strength ductility hypoeutectic Al-Cu alloys.

To overcome the disadvantage of the Arrhenius constitutive (AC) equation in predicting complex nonlinear flow behaviors, this work employed an artificial neural network (ANN) to introduce a proportional coefficient reflecting changes in softening mechanisms under various hot deformation conditions, thereby enhancing the applicability of the AC model. The result demonstrates that, compared to the AC model, the ANN-AC model effectively compensates for errors resulting from different softening mechanisms during hot deformation, with RMSE and MAPE decreasing by 62.47% and 63.75%, respectively. Additionally, the microstructure aligns with the evolution of the power dissipation factor (η) predicted by the ANN-AC model, indicating the map's accuracy. Microstructure analysis shows that discontinuous dynamic recrystallization (DDRX) grains nucleate adjacent to the original grain boundaries at low temperatures and high strain rates, while continuous dynamic recrystallization (CDRX) grains primarily form within original grains at high temperatures and low strain rates. The results reveal the effect of grain orientation on DRX, with //CD (compression direction) oriented grains capable of activating multiple slip systems, indicating a propensity for the CDRX mechanism, whereas //CD oriented grains, with fewer slip systems, promote DDRX through coordinated deformation via grain boundary motion.

Plasma arc additive manufacturing (PAAM) stands out for its remarkable efficient utilization and good performance reliability, making it a highly favored additive manufacturing technique. This study delves into the tensile deformation below δ-solvus temperature of PAAM IN718 alloy with complete heat treatment. The results show that the peak stresses are decreased from 1069 to 1189 MPa at 550 °C to 620–1059 MPa at 750 °C. Through the orientation distribution function, the domain textures for hot deformation were identified as cube texture and Rt-Goss texture {110}. The results of the observations on the substructure and grain boundary components of the deformed alloy confirmed that the onset temperature of recrystallization in PAAM alloy is approximately 750 °C. The recrystallization nucleation mechanism of PAAM IN718 alloys was identified as discontinuous dynamic recrystallization. A deformation constitutive equation for hot deformation was established using the Zener-Hollomon parameter, with an average activation energy of 508.93 kJ/mol. A processing map for the hot working of PAAM alloy was developed, and the reasonable processing domains are located at a temperature 700–750 °C/strain rate 10−2–10−1 s−1 with a power dissipation efficiency range of 0.41–0.47. The high-temperature fracture mechanism of PAAM alloy was discussed, identifying the important inducements for high-temperature fracture failure including carbides, residual Laves phase, and δ phase in the PAAM alloy.

This study systematically investigates the flow behavior of 7050 aluminum (Al) alloy produced via spray forming and subjected to a proposed pretreatment through thermal compression tests. The experimental findings reveal that the peak stress increased with decreasing deformation temperature or increasing strain rates. The parameters in the Arrhenius constitutive model were determined and verified by experimental results for spray formed (SFed) 7050 Al alloy. Hot deformation activation energy of the SFed 7050 Al alloy (147.38 kJ/mol) is notably lower than that of cast Al–Zn–Mg–Cu–Zr alloys, which is attributed to factors such as fine grains, low segregation, pores, and dispersed Al3Zr induced by pretreatment. Furthermore, processing maps have been constructed at various strains, revealing optimal stable deformation conditions at 300–450 °C/0.001–0.15s−1 and 425–450 °C/0.2–1s−1. Microstructural analysis of deformed samples highlights the critical role of dynamic recrystallization in influencing the stable and unstable areas of the alloy, which may be activated by high temperature and slow strain rate. The hot deformation mechanism of the SFed Al alloy is governed by interactions among η-Mg(Zn,Al,Cu)2 precipitates, dispersed Al3Zr particles, dislocation structures, and (sub-)grain boundaries.

We aimed to enhance p-type Bi0.4Sb1.6Te3.4 (BST) composite's thermoelectric (TE) properties by minimizing thermal conductivity through hierarchical phonon scattering via nano Ag-coated TiO2 (Ag/TiO2). Hot deformation (HD) was employed to induce multi-scale microstructures in these high-performance p-type TE materials, affecting electrical and thermal transport properties through improved textures and donor-like effects. Our optimization strategy included creating grain boundaries, multiple phonons scattering centers, and introducing high-density lattice defects, significantly reducing lattice thermal conductivity. The combined effects led to a noticeable improvement in the figure of merit (zT) across the temperature range, with all TE parameters measured along the in-plane direction. In the case of the hot-deformed Bi0.4Sb1.6Te3.4 alloy, the maximum zT reached 1.31 at 350 K, while the average zT (zTavg) was 1.17 in the range of 300–400 K, suggesting promising potential for near room temperature TE power generation and solid-state cooling.

In this study, we investigated the two-stage deformation behavior of near α Ti-6.5Al–2Zr–1Mo–1V alloy at various temperatures (915 °C, 950 °C, 1020 °C) and strain rates (0.01 s−1, 0.1 s−1). The alloy underwent differing holding periods (500s, 1000s) between deformation stages. The results demonstrated an increase in flow stress with decreasing deformation temperature and increasing strain rate. Work hardening of flow stress was observed during the two-stage thermomechanical processing within the α+β two-phase region. Microstructural evolution was characterized by the formation of α lamellar kink bands, the separation and migration of grain boundaries, and grain spheroidization. An increase in deformation temperature and a decrease in strain rate enhanced grain refinement, accelerated structural evolution, and intensified the degree of spheroidization. Dynamic recrystallization (DRX) was more prevalent at higher temperatures and lower strain rates, as the critical nucleation rate for DRX was more readily achieved. The increased interval between thermomechanical processing stages led to a transition from low-angle to high-angle grain boundaries, and a reduction in dislocation density due to static recovery occurred during the holding period. At 915 °C, hot deformation induced the formation of {10-10} twinning, altering grain orientation and reducing stress. The Schmid factor for {10-10} slip was higher at lower temperatures, which reduced the critical resolved shear stress necessary for yielding in the α phase of the Ti-6.5Al–2Zr–1Mo–1V alloy, thereby facilitating further plastic deformation.

Although different damage-coupled physically based models have been proposed, those damage models are established based on the isothermal uniaxial or multi-axial tensile condition. However, the influence of the stress state on ductile failure strain is not adequately considered in the thermal damage models. It is widely recognized that the stress state has significant effect on damage evolution and ductility fracture for metallic materials. Actually, the current damage-coupled physically based models are not suitable for complex hot forming and the applications of these damage-coupled models are mainly focused on sheet hot stamping forming to date. Therefore, a modified damage-coupled unified model considering a broad range of stress states was established to figure out the complex damage behavior and microstructure evolution of metallic materials during the thermal deformation process. In this study, the Mg-6Gd-5Y-0.3Zr alloy was used as the experimental material. First, the flow behavior of the alloy was explored using a series of experiments under various stress states (i.e., uniaxial tensile, shear and compression) under various combinations of strain rates and temperatures. On this basis, a modified damage-coupled physics-based model was developed, in which the dynamic recrystallization, damage, stress triaxiality and Lode parameter were included as internal state variables. Furthermore, the model was integrated into ABAQUS to verify the applicability using hot spinnability test because the stress state was very complex during the forming process. The comparison between the calculated results and experiments is carried out. According to the simulation result, the predicted ultimate thinning rate is 71.14%, with an error of only 7.85% from the experimentally measured ultimate thinning rate of 77.2%, and the correlation coefficient and error for thickness and profile between the predicted values and experimental values are 0.9980 and 5.05%, respectively. These demonstrate that the developed model is reliable.

Hot compression experiment was conducted on Gleeble-3800 thermal simulation testing machine to investigate the hot deformation behavior of Cr5 die casting mold steel, with deformation temperatures of 1100–1300 °C and strain rates of 0.01−10s−1. The experimental results indicated that deformation temperature and strain rate have significant impacts on dynamic recrystallization(DRX) of Cr5 die casting mold steel, the critical strain of DRX decreased as deformation temperature increased and strain rate decreased. According to the Arrhenius model, the activation energy for deformation was 427.85 kJ/mol, and the constitutive equation of hot deformation was derived. Validation of high temperature flow stress model showed that the fitted model emerged appreciable accuracy and reliability. The processing map was constructed based on DMM theory, which was concluded that the unstable region is mainly concentrated around the deformation condition of 1300 °C/10s−1. Cr5 die casting mold steel exhibits the best hot processing performance under the deformation condition of 1250 °C/0.1s−1, with an excellent efficiency of power dissipation(η = 0.36) and a lower value of Kernel average misorientation(KAM average = 1.675°). Discontinuous dynamic recrystallization (DDRX) is the main mechanism for recrystallization nucleation and growth during hot deformation of Cr5 die casting mold steel.

The dissolution mechanism of the η-Ni3(Al0.5Nb0.5) phase during hot compression in Ni-based ATI718Plus superalloy has been investigated. The results indicate that with increasing deformation, the amount of dynamic recrystallization grains in the γ matrix increases, and the dissolution of the η phase tends to be accelerated. At the precipitation temperature of the η phase of 950 °C, the η phase area fraction decreased from 9.8% to 3.0% after deformation. The deformation promotes dislocation accumulation at the boundaries of the η phase, developing into subgrains and then evolving into DRX grains due to subgrain rotation. With increased strain, the subgrain rotations and DRX grain growths result in extrusion and subsequent fracture of the η phase. Due to strain incompatibility between the η phase and γ matrix, dislocation sustains are accumulated at their interfaces, which disrupts the η/γ semi-coherent interface, leading to localized amorphization and the decomposition of the η phase. Furthermore, dislocation surrounding the η phase can act as diffusion channels for solute elements, promoting the dissolution of the η phase and resulting in the element concentration gradient distribution from the η phase to the γ matrix.

The automotive industry has experienced rapid growth, with lightweight materials becoming a significant research focus. Among these materials, low-density Fe–Mn–Al–C alloys show promise for this kind of application. To optimize the hot workability parameters of these alloys for practical applications, it is essential to explore the hot deformation behavior of these alloys. In this study, we investigated the hot deformation behavior of the low-density alloy Fe-0.77Mn-7.10Al-0.45C-0.31Nb using hot plane-strain compression tests for several deformation temperatures (850, 950, 1050, and 1150 °C) and nominal strain rates (0.01, 1, and 10 s−1). Unusual flow stress curves were observed for low (0.01 s−1) and intermediate (1 s−1) strain rates, with discontinuous yielding and multiple stress peaks. This high-temperature behavior is associated with non-homogeneous strain partitioning in duplex microstructure (δ-ferrite + γ). Using the Zenner-Hollomon constitutive modeling approach, we estimated the thermal activation energy for hot deformation as 297 kJ/mol from the experimental peak flow stresses. Additionally, processing maps and microstructure correlation analysis revealed that the alloy exhibits good hot workability in the 975–1075 °C temperature range under low and intermediate strain rates (0.01–0.3 s−1). Under these processing conditions, the δ-ferrite microstructure is submitted to dynamic recovery, while the austenitic phase undergoes dynamic recrystallization.

A powder-metallurgy MoNbTaTiV refractory high-entropy alloy synthesized by mechanical alloying (MA) and spark plasma sintering was subjected to hot deformations at different temperatures and strain rates. The microstructural morphologies were characterized, and component element segregation was elucidated. With grain refinement and lattice strain increase, the large inhomogeneous milled powder became refined and homogeneous after the MA. Component element segregation was observed at relatively low deformation temperatures and high strain rates. As the deformation temperature increased and the strain rate decreased, the segregation gradually disappeared, which was attributed to dislocation movement.

Precipitates always have a complex effect on the hot work hardening and recrystallization softening of materials. In this work, the dual effect of V-microalloying on hot deformation behavior and microstructure evolution of high nitrogen martensitic stainless steel (HNMSS) was investigated by hot compression experiments, modeling study and microstructure characterization. The results showed that V-microalloying enhanced the flow stresses and activation energy of 0.2V steel due to the fine grain strengthening effect and the blocking effect of dynamic precipitation on dislocation movement and grain boundary migration. On the other hand, the recrystallization model and deformed microstructure indicated the more intense dynamic recrystallization (DRX) softening effect in 0.2V steel, inducing the faster decrease of flow stress after the peak stress. V-microalloying promoted the dynamic precipitation of HNMSS during hot deformation, which reduced the size and increased the number of precipitates in 0.2V steel. The fine precipitates hindered dislocation movement, promoted dislocation accumulation and entanglement, formed a particle deformation zone (PDZ) with high dislocation density and large orientation gradient, and then induced the occurrence of particle-stimulated nucleation (PSN). In addition, the dislocation cells evolved from dislocation entanglement were also favorable nucleation sites for DRX.

The recent discovery of multicomponent principal alloys and the enhanced comprehension of their physical metallurgy have significantly advanced the understanding of microstructure engineering and material selection for high-tech applications. The exceptional combination of characteristics found in MEAs can be attributed to their distinctive phase constitution, which is aided by their multi-principal constituents. These properties are seldom encountered in ordinary alloys. Nevertheless, the use of these materials in their as-cast state is challenging due to issues such as the presence of heterogeneity in their chemical makeup, shrinkage porosity, unrefined dendritic structure, and the presence of a quasi-stable eutectic at grain boundaries. Consequently, the utilization of hot deformation methods for the purpose of achieving uniform and refined microstructures in as-cast MEAs has garnered significant interest as a viable approach to address these limitations. This review provides a comprehensive summary of the hot deformation characteristics of MEAs. Factors such as the alloy composition, the phase constituent, deformation parameters and recrystallization mechanisms were observed to influence the microstructural development and phase transition, flow curve characteristics, and mechanical characteristics of MEAs. Additionally, the use of processing map analysis for the determination of optimal processing zones for the hot deformation of MEAs was appraised. The discussion also encompassed the constitutive model description, molecular dynamics modeling, and machine learning algorithm for the prediction of the governing deformation mechanism and the deformation flow stress. Finally, future research directions are suggested.

The hot deformation behavior and microstructure of Fe-12.5Cr–4Al–2Mo-0.03Nb-0.08Y alloy were studied under conditions of 800 °C–1200 °C/0.01 s−1∼10 s−1 using a combination of hot compression experiments, EBSD and TEM characterization. The results indicate that the deformation temperature and strain rate have a significant impact on the flow stress and microstructure of the alloy, especially the deformation temperature. The constitutive equation constructed in this paper can reflect the hot deformation process and accurately calculate flow stress value of the FeCrAl alloy in corresponding states. The FeCrAl alloy undergoes DRV and DRX during hot deformation. DDRX grains distributed along the original grain boundaries mainly formed at low deformation temperatures and high strain rates, while CDRX grains mainly formed at high deformation temperatures and low strain rates and characterized by the internal distribution of the original grains. Moreover, the orientation of DDRX grains is mostly different from that of adjacent original grains, while the orientation of CDRX grains is relatively close to that of the original grains.

Dynamic recrystallization (DRX) and deformation twinning play a pivotal role in stress partitioning during hot deformation of magnesium alloy. However, the influence of twinning on stress is diverse, and the interaction between DRX and twinning is intricate. Existing constitutive models cannot simultaneously describe the relationship between DRX and twinning, as well as their effects on stress. In this study, the hot compression tests were conducted to study the flow behavior and microstructure evolution of AZ31. The obtained flow curves and microstructure revealed that AZ31 alloy undergoes simultaneously DRX softening and twinning hardening during hot deformation. Furthermore, texture evolution was significantly influenced by both DRX and twinning behaviors. As a result of DRX behavior, there was a decrease in twin volume fraction in the later stages of deformation. Consequently, a twin volume fraction model that incorporates the inhibitory effect of DRX was proposed. According to the experimental results of high temperatures and low strain rates, a constitutive model incorporating work hardening, dynamic recovery (DRV), and DRX was established. Additionally, the influence of twinning on flow stress was incorporated into the model, resulting in a constitutive model that considers both DRX and twinning simultaneously. Finally, the proposed model's reliability was validated through the wedging spinning process, successfully predicting both macroscopic deformation and microstructure evolution of the spinning parts.

The hot deformation behavior and the associated microstructural evolution (which were the keys to decide mechanical properties) were studied using different deformation conditions for the quaternary Al–Cu–Li–Zn alloy containing 1.0 wt% Zn. The constitutive equations and processing map were established. Dynamic recrystallization (DRX) was related to the orientation of the initial grains. The DRX rarely occurred in the grains with an orientation near Al and mainly occurred in the grains with an orientation near Al. Particle simulated nucleation (PSN) promoted by pre-existed coarse T1 phase particles was the main mechanism of the DRX when the deformation temperature was below 450 °C. In the temperature range of 450–500 °C with a strain rate of 0.01 s−1, the DRX occurred by grain boundary bulging or the increase in the cumulative misorientation, but only small fraction of the DRX grains appeared. This work provided an important guideline for the optimization of deformation techniques and microstructures.

The hot compression tests of Fe–28Mn–11Al–1.5C–5Cr (wt.%) lightweight steel were carried out by Gleeble-3500 at temperature of 900, 1050 and 1150 °C with strain rates of 0.01 and 1 s−1. The effect of various precipitates on the hot deformation mechanism and dynamic recrystallization (DRX) mechanism was studied by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). When deformed at 900 °C, the dislocations tend to cut through intragranular κ carbides to form unidirectional microbands and deformation twins. The intergranular precipitates (intergranular κ carbides, B2 (FeAl type) precipitates and (Cr,Mn)23C6 precipitates) hinder the migration of the original grain boundaries, so that the discontinuous DRX (DDRX) is suppressed at the initial stage, but with the increase of strain, the dislocations accumulate at the grain boundaries to promote the nucleation of DRX grains. Meanwhile, the nucleation of DRX grains by continuous DRX (CDRX) mechanism within grains is also activated. Therefore, bimodal distribution of DRX grains is formed at low strain rate of 0.01 s−1, while the degree of DRX is low at high strain rate of 1 s−1. When the deformation temperature is 1050 °C, the content of microbands and deformation twins decreases. There are only a few B2 precipitates at the grain boundaries, so the original grain boundaries tend to bulge to promote DDRX nucleation. When deformed at 1150 °C, large-sized κ carbides are easily formed near the dislocations due to the fast diffusion rate of atoms, which inhibits the formation of microbands and deformation twins, and only slip bands are observed. There is no precipitate on the grain boundary, and the DDRX is the dominant mechanism of DRX. Moreover, the special yield-point-like elongation phenomenon has been proved to be caused by intragranular κ carbides.

A new titanium alloy with chemical composition of Ti–6Al–1Mo–1V–2Zr–2Cr–1Fe (wt.%) is designed and produced. The hot deformation behavior, microstructural evolution and texture evolution of the alloy after solution treatment are investigated in this paper. Firstly, the constitutive equation of solution-treated Ti–6Al–1Mo–1V–2Zr–2Cr–1Fe alloy with the consideration of strain compensation is obtained based on compressive test at the temperatures of 950–1100 °C and the strain rates of 0.01–10 s−1, which can be used to describe the flow behaviour at elevated temperatures. According to the corresponding constitutive equation, the flow stress of solution-treated alloy is accurately predicted, which is further verified by the experimental data. Furthermore, discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) are observed in the microstructures of the deformed alloys, where deformation temperature and strain rate have a significant effect on DDRX and CDRX processes of solution-treated Ti–6Al–1Mo–1V–2Zr–2Cr–1Fe alloy. Moreover, plastic deformation and dynamic recrystallization have a comprehensive influence on the texture evolution of solution-treated Ti–6Al–1Mo–1V–2Zr–2Cr–1Fe alloy. ηbcc-fiber textures of {100} and {110}, εbcc-fiber texture of {112} and ξbcc-fiber texture of {110} are the main texture compositions of the deformed samples, where all of the deformed samples exhibit a strong {100} texture.

Nanocrystalline Ce–Fe–B alloys exhibit potential utilization for low-cost permanent magnets, however, the preparation of anisotropic magnets with satisfactory magnetic properties remains a challenge. CeFe2 Laves phase with high melting point that forms in the Ce-rich Ce–Fe–B magnets has been considered as the reason to be detrimental to its hot-working process and magnetic performance. Herein, we report the significant effects of adding Ga to nanocrystalline melt-spun Ce17Fe78-xB6Gax alloys on suppressing the CeFe2 phase and enhancing coercivity. The x = 2.0 alloy is identified as the optimal precursor for preparing anisotropic hot-deformed magnet due to its lower CeFe2 phase content (5.7 wt.%), considerably less than that of the ternary Ce–Fe–B alloy (17.6 wt.%). The congruent alignment and platelet-shaped grain characteristics are obtained in the Ga-added hot-deformed magnet, indicating an enhanced anisotropy that results in an improved remanence from 4.2 kGs to 5.9 kGs. The development of such texture can be ascribed to the reduced amount of CeFe2 phase, allowing the formation of Ce-rich grain boundary (GB) phase, which is necessary to induce grain alignment during hot deformation process. Two types of Ga-containing GB phases are found in the Ga-added magnet, namely typical Ce-rich/Fe-lean GB phase and Ce6Fe13Ga phase. The uniformly distributed Ce-rich GB phases surrounding the main grains helps to magnetic isolate the Ce2Fe14B grains and thus enhance the coercivity, as verified by detailed microstructural characterizations combined with micromagnetic simulation. The work offers a potential way to realize anisotropy in Ce–Fe–B magnets and inspires further exploration of high abundance Ce-based magnets.

The present study dealt with the hot compression deformation behavior of Fe−18.5Mn–7Cr−0.6C and Fe−18.5Mn–7Cr−0.6C−0.21 N high-Mn austenitic steels within a temperature range of 900–1200 °C, a strain rate range of 0.01–5 s−1, and a true strain of 0.7. The accurate constitutive equations were established according to their flow curves, and the deformation microstructures were also analyzed. The results revealed that the dominant softening mechanism for the two test steels without substantial peak stress (higher Zenger-Holloman parameter values) could also be dynamic recrystallization (DRX) rather than dynamic recovery (DRV). The addition of N enhanced the strain rate sensitivity of high-Mn austenitic steel at low temperatures and high strain rates. Furthermore, the addition of N increased the high temperature strength and hot deformation activation energy (Q) of high-Mn austenitic steel. Moreover, the addition of N could also increase the DRX volume fraction and refine the DRX grain size of high-Mn austenitic steel.

The hot-working behavior of high-Mn austenitic steel for liquefied natural gas carriers at the deformation temperature in the range of 1073–1273 K and the strain rate in the range of 0.01–10 s−1 was studied on a Gleeble-3800 thermomechanical simulator using a compression test. Electron backscatter diffraction was used to study the microstructure after deformation. Under each deformation condition, a peak stress appears in the stress-strain curve, which conforms to traditional dynamic recrystallization hot-working flow stress curves. A hyperbolic sine-law-type constitutive equation was established to predict the peak stress. The thermal deformation activation energy was 414.19 kJ/mol, and the stress index n was 4.94. The texture of the deformed grains consisted of strong and weak fibers along the compression direction. The main recrystallization mechanism was discontinuous dynamic recrystallization. The grain size of the discontinuous dynamic recrystallization grains tended to increase with increasing deformation temperature or decreasing strain rate. Processing maps were drawn based on the dynamic material model. At high deformation temperatures, the power consumption factor of dynamic recovery was greater than that of dynamic recrystallization, whereas at low deformation temperatures, the power consumption factor of discontinuous dynamic recrystallization was greater than that of dynamic recovery. There are two flow instability regions in the processing maps, 1243–1273 K/1-10 s−1 and 1073–1203 K/0.05–10 s−1. The formation of a ‘necklace microstructure’ was the main cause of deformation instability. The optimized process parameters for industrial production were 1243–1273 K/1-10 s−1.

The formation of prior particle boundaries (PPBs) in a new powder metallurgy superalloy during hot isostatic pressing (HIP) is investigated. Also, the impact of subsequent hot deformation on the elimination of PPBs is systematically studied. The PPBs involves large γ′ phases, carbides (MC and M6C) and oxides (Al2O3, SiO2 and ZrO2). The reactions among the superficial oxides, the adsorbed C and O elements on the particle surface and internally-migrated alloying elements are the dominant reasons for the formation of PPBs during HIP. Besides, the existence of surface tension and surface energy induces the carbon segregation, as well as the formation of PPBs. Thus, the density of PPBs decreases when the spacing between powders is shrunk by a rapid deformation. In hot forming process, the PPBs can be efficiently eliminated via raising deformation temperature/true strain or reducing strain rate. The interactions between dislocations and PPBs, as well as the occurrence of dynamic recrystallization (DRX) induced by the strain/orientation gradient, lead to the elimination of PPBs. The thermodynamic stability of carbides declines with the raised temperature. It indicates that the dissolution of carbides and the elimination of PPBs can be accelerated via raising the deformation temperature. The breakage or deformation behavior of PPBs during hot extrusion is investigated by numerical simulation. The deformation degree of PPBs increases with the raised extrusion ratio. The above important findings are useful for developing hot extrusion processing to effectively eliminate PPBs.

In this work, we systematically evaluated the effect of Si on the dynamic recrystallization (DRX) during hot deformation behavior of a novel high-strength rolled Medium Mn steel. To this end, the novel steel was subjected to compression test in the temperatures of range temperature of 950–1150 °C and the strain rate of range of 0.01–10 s−1. Numerical simulation, constitutive analysis, different models and processing maps were also developed to predict the volume fraction of DRX, which was further confirmed through electron backscatter diffraction (EBSD). The results show that some disparities are existed between the model predictions and the results. The EBSD micrographs of samples displayed prominent discontinuous DRX peak in the true stress-strain curves exhibit conventional equiaxed DRX particles. Most specifically, in initial stages the addition of Si increased the DRX and grain boundary migration, and the later stages of deformation the DRX was triggered after achieving the steady state. Therefore, the final microstructure appears as elongated austenite or localized DRX. Furthermore, the work hardening stage before the new round of DRX nucleation caused the stress to continue to increase after the steady state. These findings provide valuable insights into the complex behavior of materials under the influence of Si addition and enhancing our understanding of microstructural evolution during hot deformation.

An accurate constitutive model is imperative to describe the deformation behavior of aluminum alloy in numerical simulation of thermal plastic forming process. In this study, isothermal uniaxial compressions of 2A12-T4 aluminum alloy were conducted by Gleeble-3500 thermal-mechanical simulator under the temperature of 300–450 °C and strain rate of 0.01–10 s−1. Three different Arrhenius constitutive models, including strain compensation (SC), genetic algorithm (GA) and K-function modification (KM), were established basing on the double correction of the true stress–strain curve by considering the effect of temperature variation and interfacial friction. The prediction accuracy of three models were assessed by the correlation coefficient (R), average absolute relative error (AARE) and the logarithm of the mean square error (ln (MSE)). The results show that the newly KM constitutive model considering the coupling effect of temperature and strain rate showed excellent agreement with the experimental data and best prediction capability with lowest error. Hot processing map based on the Murty-Rao criterion shows that high temperature and low strain rate is suitable for stable forming. In order to verify the reliability of the proposed model in numerical simulation, the established KM Arrhenius constitutive equation is secondarily developed in DEFORM 3D software and used in the hot compression process under the stable forming conditions obtained from hot processing map. The simulated force–displacement curves and maximum load values under forming conditions were well match with the experiment trends, which proved the reliability of the KM constitutive equation in the finite element numerical simulation.

The discovery of High entropy alloys (HEAs) and the deepened understanding of their physical metallurgy have raised the bar on microstructure design and choice materials selection for highly specialized, sensitive technological and structural integrity applications. This is on account of their unique phase constitution, facilitated by their multi-principal elemental compositions, which imparts excellent properties combinations in HEAs, which are rarely observed in conventional alloys. However, due to their shrinkage porosity, chemical composition heterogeneity, rough dendritic structure, and quasi-stable eutectic at grain boundaries make direct deployment in the as-cast condition, is problematic. As a result, using hot deformation techniques to create homogenous and fine microstructures in as-cast HEAs has gained attention as an effective strategy to resolve these shortcomings. A systematic review of studies on the hot deformation behaviour of different classes of high entropy alloys (HEAs), is summarized in this review paper. The plastic flow behaviour, phase, and microstructural evolution, mechanisms of hot deformation as well as the optimal hot deformation processing regions, derived from analysis of processing maps, were evaluated in this review. Factors such as alloy constitution, HEA phase(s) type, deformation processing parameters, and recrystallization mechanisms, were noted to influence the nature of microstructural evolution, plastic deformability, and material properties of the HEAs. The role and effectiveness of processing maps in establishing conditions for optimal tuning of the microstructures in HEAs to achieve the best product finish were also discussed.

The hot deformation behaviors and softening mechanism of 6%Si high-silicon austenitic stainless steel were investigated under deformation conditions of 1000–1200 °C/0.01–10 s−1. The constitutive equation was established based on the stress-strain curves, and the processing maps were drawn based on the Dynamic Material Model (DMM) at different strain levels. The results show that the activation energy(Q) of hot deformation is 368.555 kJ/mol. The peak region of the hot processing maps is 1130–1170 °C/0.01–0.03 s−1 at the strain of 0.7, the η value is 0.47, indicating that the best hot workability can be achieved in this region. At high strain rates (1000–1200 °C/0.66–10 s−1), the material is easily destabilized, while in the non-destabilized zone, η values are greater than 0.3, excluding the processing danger zone, and a better microstructure can be obtained. The accuracy of the processing maps established in this paper was verified by combining the microstructural morphology of different regions with the processing maps. Under the deformation conditions of 1200 °C/0.01 s−1, the χ phase and a small amount of δ ferrite are precipitated. The second phases induce the occurrence of a fracture along the grain while refining the grain size. Therefore, processing should be avoided in the range of second-phase precipitation. Crystallographic information analyses showed that the softening mechanism of high-silicon austenitic stainless steel is mainly discontinuous dynamic recrystallization (DDRX), and continuous dynamic recrystallization (CDRX) occurs in the softening mechanism between 1100 and 1150 °C.

The mechanical properties and related mechanisms of the Ti–6Al–4V alloy solid-state diffusion bonding (SSDB) joint under elevated temperature conditions have been experimentally investigated in this study. Tensile tests with temperatures (298 K–1173 K) and strain rates (0.001 s−1, 0.1 s−1) of the joint and base metal (BM) were carried out. The microstructural evolutions were characterised by optical microscope, scanning electron microscope combined with backscatter diffraction. The results show that the tensile strength and elongation of the joint are slightly lower than the BM at 298 K, which is attributed to the higher Schmid factor and unbonded areas of the joint. However, at elevated temperatures from 1023 to 1123 K, the tensile strength of the joint turns to be higher than the BM, while the elongation of the joint is much lower than the BM. Grains with relatively high Taylor factors cluster at the DB interface. The larger number fraction of high angle grain boundaries (HAGBs−88%) and a higher inclination of strain hardening at DB interface, cause a higher strength of the joint at high temperatures. No significant plasticity variation of the joint is revealed because of primitive remnant holes and new straight HAGBs at DB interface. While when the temperature further increases to 1173 K, the difference of properties between the joint and BM become negligible. Corresponding reasons are characterized as dynamic recrystallization occurs at the interface of the joint at 1173 K, which is 50 K higher than that of BM, and the interface is eliminated.

This review article provides an in-depth discussion on the hot deformability, processing map analysis, and microstructural development in superalloys, as well as the associated constitutive equations employed in flow stress prediction. It describes how hot working can improve the grain structure of superalloys by dynamic recrystallization (DRX), reduce defects, and enhance their mechanical characteristics. The formation of necklace structures, work-hardening analysis to identify the existence and commencement of dynamically recrystallized grains and the influence of processing conditions on DRX grain size are all addressed in this article. The influence of deformation variables, described by the Zener-Hollomon parameter - the occurrence of phases, dynamic precipitation, and alloying elements on the thermomechanical response, and the restoration processes of DRV and DRX are discussed in detail. The utilization of processing maps as a means to determine the most favourable processing conditions and identify the instability regime, encompassing flow instability, defects and cracking, that may arise during the hot-working of superalloys are discussed. Specifically concerning the constitutive modelling of flow stress for characterizing material flow (at various deformation strain rates, temperatures, and strain), the application of threshold stress (as a result of phase transformation during hot deformation), temperature-dependent Young's modulus, and comparing the experimentally observed activation energy and deformation stress exponent to the values predicted by creep theories, are discussed. Also, an analysis of the various modelling techniques and equations for predicting flow curves during hot-working processing is evaluated. Finally, some recommendations are made regarding the potential future research directions.

Hot compression tests in the temperature range of 493-653 K and strain rates of 0.01-10.00 s−1 were used to evaluate the hot deformation behavior of 60Mg-30Pb-9.2Al-0.8B alloy. In order to optimize the hot working parameters, the Arrhenius constitutive equation and processing map with strain compensation were established on the dynamic material model (DMM). The results show that the stress-strain curves have three different stages of rising, peaking, and steady state during the hot compression with typical characteristics of work hardening (WH), dynamic recovery (DRV), and dynamic recrystallization (DRX). In addition, the improved Arrhenius strain compensation constitutive model has a higher precision than the traditional constitutive model. By dividing the processing map into three typical regions for analysis, the maximum power efficiency is obtained at ε = 0.4. The optimum hot working parameters are temperature range of 573K∼653K, and strain rate range of 0.01 s−1∼0.1 s−1. Instability usually occurs in the region with high strain rate and low temperature, and the main form of instability is cracking.

The study aims to investigate the hot deformation behavior of Co–Cr–Fe–Ni–V high entropy alloy (HEA) at temperatures ranging from 1073 K to 1373 K and strain rates of 0.001, 0.01, 1, and 10 s−1, and to generate processing maps using dynamic materials modeling (DMM) to identify the optimum processing domain for industrial applications. The material's hardening and softening characteristics are also explored under various hot working conditions. Deformation twinning is observed in materials deformed at 0.1 s−1 at 1273 K and 1373 K, contributing to their observed hardening. The mean free path of dislocation defines the material's strength, and the transition point from dynamic recovery to dislocation-dislocation or dislocation-solute interaction occurs when the mean free path of dislocation reaches its lowest value. The inhomogeneity in the deformed sample is correlated with the strain field distribution using an integrated approach using finite element method (FEM) modeling and electron backscattered diffraction (EBSD) results. EBSD characterization reveals the presence of deformation bands and annealing twins at low and high temperatures, respectively. Additionally, an artificial neural network (ANN) model is proposed to predict the hot deformation behavior of Co–Cr–Fe–Ni–V HEA, with promising results, as evidenced by a correlation coefficient (R) of 0.9983 and an average absolute relative error (AARE) of 2.71% on the test dataset.

Hot tensile features of a commercial 7046 aluminum alloy are investigated through employing high-temperature tensile tests. The evolving mechanisms of microstructures over high-temperature tensile parameters are systematically revealed. A unified dislocation-density related constitutive model is proposed to reconstruct hot tensile stress–strain behaviors. Results imply that the microstructural evolving features are acutely influenced by tensile parameters. The principal softening mechanism converts from dynamic recovery (DRV) to dynamic recrystallization (DRX), as the tensile temperature reaches 350 °C or above. The combined DRX nucleation features containing discontinuous DRX (DDRX) as well as continuous DRX (CDRX) together emerge. Furthermore, the CDRX behavior characterized by substructural nucleation and interaction becomes apparent at low tensile temperature or high strain rate, while the DDRX process is weaken. Through validation, the reproduced tensile stress, grain size as well as DRX fraction are good accordance with experimented values, which proves the proposed dislocation-density related equation can enjoy an outstanding reproduced capacity for the thermal tensile features of a 7046 aluminum alloy.

In this study, the mechanical responses of Ti–6Al–4V alloy sheets at a high temperature under multi-axial loading were investigated using a micromechanics-based damage model within a continuum finite element (FE) framework. Tensile tests at three strain rates and a high temperature were conducted to analyze the plastic and ductile damage properties of the Ti–6Al–4V alloy sheets. Additionally, hot Nakajima tests were conducted on specimens with three different shapes to evaluate the improvement in formability at a high temperature. Moreover, the dimples on the fractured surfaces of the experimental samples were qualitatively analyzed. Simultaneously, corresponding FE simulations were conducted to predict the ductile damage behavior of the Ti–6Al–4V alloy sheets at a high temperature using a modified Gurson−Tvergaard−Needleman model. The predicted results and the displacements at the onset of failure were compared with the corresponding experimental data.

The current study investigates the high-temperature deformation behaviour, and microstructural evolution of the laser powder bed fused, Ti modified Al 2024 alloy. The high-temperature performance was evaluated using a hot compression test performed in the temperature range of 200–350 °C and strain rate range of 0.1–10 s−1. The flow behaviour at elevated temperatures at different strain rates can provide us insight into the high temperature application and can also be utilized for optimization of deformation-based post processing technique. The deformation-based post processing method utilizes work hardening to improve the mechanical properties and to reduce the inherent defect of additively manufactured parts, such as pores and lack of fusion. The optimal deformation conditions for these processes can be obtained from the processing map. The flow stress during different deformation conditions (strain, strain rate and temperature) was predicted using different phenomenological models such as Johnson-Cook (JC) model, strain compensated Arrhenius equation, and artificial neural network (ANN). The JC model was observed to be the least suited method in the current investigation, whereas the ANN method was observed to be best suited for predicting flow stress with an average absolute relative error of 0.5% and a correlation coefficient of 0.9998. Different deformation mechanisms such as dynamic recovery (DRV) and dynamic recrystallization (DRX) were investigated for different deformation conditions using empirical models, finite element analysis (FEA) and microstructural characterization using TEM, and EBSD. The primary DRX mechanism in the current study was observed to be continuous dynamic recrystallization or CDRX mechanism.