Search

To further investigate the properties of Incoloy825/P110 bimetallic composite seamless pipes, thermal deformation analysis was conducted on their billets. The thermal deformation and dynamic recrystallization (DRX) behavior of Incoloy825/P110 bimetallic composite materials were studied through hot compression tests at deformation temperatures (850–1150 °C) and strain rates (0.01–10 s−1). A constitutive relationship was established, and compensation and correction were made based on the differences in materials corresponding to different strain states. The hot processing map was established based on the thermal deformation behavior of bimetallic materials. In addition, the evolution of microstructure was also studied to verify the feasibility of the established hot processing map. The results show that the strain compensated Arrhenius can accurately predict the flow stress. By analyzing the microstructure using EBSD, it can be found that DRX behavior has a significant impact on the thermal processing properties of composite materials. This study provides an important theoretical basis for the production of Incoloy825/P110 bimetallic composite seamless pipes in the future. [ABSTRACT FROM AUTHOR]

The hot compression experiments were performed at a deformation temperature of 720 °C to 870 °C and a strain rate of 0.0005 s−1 to 5 s−1. The strain‐compensated Arrhenius constitutive equation and the hot processing map at a strain of 0.6 were established, and the dynamic recrystallization behaviors of the alloy in different power dissipation (η) regions were studied. The results show that the correlation coefficient (R) and average relative errors (AARE) of the established constitutive equations are 0.999 % and 2.523 % in the β phase region, and 0.988 % and 7.709 % in the α+β phase region, respectively. The hot processing map shows that the deformation parameters in the high power dissipation regions range from 810 °C to 870 °C/0.0005 s−1 to 0.005 s−1, accompanied by a power dissipation factor of 0.41 to 0.55. These regions result from a combination of continuous and discontinuous recrystallization mechanisms. With the decrease in the power dissipation value, the appearance of deformation bands (DBs) and localized flow (FL) in the microstructure increased. [ABSTRACT FROM AUTHOR]

It is important to explore the hot deformation behavior and establish the hot processing map of steel to design and optimize the hot rolling process. In this paper, 50CrVA spring steel was used as the experimental material. Single-pass compression tests were performed at 850–1150 °C and 0.01–5 s−1 on an MMS-300 thermo-mechanical simulation testing machine to investigate the hot deformation behavior and establish the hot processing map. The results show that as the strain rate increases and the deformation temperature decreases, the flow stress of 50CrVA spring steel increases. The constitutive equation of 50CrVA spring steel is ε ˙ = 1.01 × 10 14 [ sinh (0.0094 σ p) ] 4.53 exp (− 364 , 470 R T ) . The dynamic recrystallization critical strain model is ε c = 4.19 × 10 − 3 Z 7.31 × 10 − 2 . A hot processing map of 50CrVA spring steel was constructed to determine the plastic instability region and optimal hot working region. [ABSTRACT FROM AUTHOR]

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

The present study prepared 7075Al composites reinforced with vapor-phase-grown carbon nanofibers (VGCNFs) using the spark plasma sintering (SPS) method. Constitutive equations of the composites were calculated, and thermal processing maps were constructed by performing thermal compression tests on the VGCNF/7075Al composites at deformation temperatures ranging from 300 to 450 °C and strain rates from 0.01 to 1 s−1. This study analyzed the microstructural evolution of the VGCNF/7075Al composites during the thermomechanical processing. The experimental results demonstrated that dynamic recrystallization (DRX) primarily governed the softening mechanism of VGCNF/7075Al composites during thermomechanical processing. At high strain rates, a combination of dynamic recovery (DRV) and DRX contributed to the softening behavior. The incorporation of VGCNFs results in higher dislocation density and a larger orientation deviation within the 7075Al matrix during the thermomechanical deformation process, providing stored energy that facilitated DRX. The activation energy for deformation of VGCNF/7075Al composites was 175.98 kJ/mol. The constitutive equation of the flow stress showed that a hyperbolic sinusoidal form could effectively describe the relationship between flow stress, strain, strain rate, and temperature of VGCNF/7075Al composites. The optimal thermomechanical deformation parameters for VGCNF/7075Al composites were 400–450 °C and 0.01–0.1 s−1 when the strain ranged from 0.05 to 0.15. For strains between 0.25 and 0.35, the optimal thermomechanical parameters were 380–430 °C and 0.01–1 s−1. [ABSTRACT FROM AUTHOR]

The increasing demand for high-strength lightweight hollow shafts in transportation highlights the need for advanced fabrication techniques. Al–Zn–Mg–Cu alloys, noted for their superior properties, are selected for three-roll skew rolling (TRSR). In TRSR, the material undergoes combined axial tensile and radial compressive stresses. This study evaluates the feasibility of TRSR for producing high-strength lightweight hollow stepped shafts from Al–Zn–Mg–Cu alloy. An integrated approach, including constitutive modeling, hot processing map development, and TRSR numerical simulations/experiments, is employed to optimize the TRSR forming process. The constitutive model was established based on 300°C–450 °C & 0.01–10 s−1 hot compression and 350°C–430 °C & 0.1–5 s−1 high-temperature tensile test data. The established Johnson-Cook optimization by genetic algorithms (GA-JC) model and unified viscoplastic constitutive model, accurately capture the alloy's hot deformation behavior, exhibiting minimal average absolute relative errors (AARE) of 5.431% and 5.808%, respectively. Microstructure evolution analyses shed light on the predominant softening mechanisms, emphasizing dynamic recovery (DRV) at elevated strain rates and diminishing texture intensity with escalating deformation temperatures. The composite hot processing map delineates optimal process parameters (400°C–450 °C & 0.1s−1-1s−1), facilitating informed decision-making in manufacturing practices. The validation of numerical simulations through TRSR forming experiments with initial temperature of 450 °C for the billet and axial moving speed of 10 mm/s for the chuck in affirms the feasibility of producing hollow stepped shafts from high-strength Al–Zn–Mg–Cu alloy. Close agreement was found between simulated and experimental wall thickness variations. This study enhances understanding and optimization of TRSR forming for high-strength lightweight alloys, advancing industrial manufacturing methodologies.

In this study, a Zwick 1484 machine was employed to conduct hot compression experiments on a Mg-12Gd-3Y-0.6Zr alloy (GW123 magnesium alloy) at deformation temperatures ranging from 360 to 480 °C and strain rates from 10−3 to 10 s−1. A dataset comprising deformation temperature, strain, strain rate, and stress was built based on these experimental conditions, and the strain-compensated Arrhenius model and the backpropagation artificial neural network (BP-ANN) model were developed to investigate the hot deformation behavior of the GW123 magnesium alloy. The results show that the BP-ANN model has a correlation coefficient of 0.9986 and an average absolute error of 1.53, whereas the Arrhenius model has a correlation coefficient of 0.9729 and an average absolute error of 13. The reason for this result is that the BP-ANN model, by leveraging more data points (1500 in total) to optimize its adaptive parameters, can effectively capture complex nonlinear relationships between different deformation conditions simultaneously, thus providing superior accuracy in predicting the true stress–strain curve responses compared with the Arrhenius model. Furthermore, the optimal processing parameters for the GW123 magnesium alloy were determined through hot processing maps to be within the temperature range of 440–480 °C and strain rates of 10−3 s−1 and 10−2 s−1. [ABSTRACT FROM AUTHOR]

The evaluation of the hot workability of 5Cr5MoSiV1 steel with high deformation resistance is crucial for the controllability of the hot forging process. Based on the isothermal compression at deformation temperature of 950–1200 °C and strain rate of 0.01–10 s−1, the flow behavior of 5Cr5MoSiV1 steel is demonstrated. As the strain rate increases, the typical characteristics of the true stress–strain curve indicate that the dynamic softening mechanism changes from dynamic recrystallization to dynamic recovery. Moreover, the hot working window determined by the hot processing map from the modified J–C constitutive model is constructed for the forging process of the material. Through microstructure verification, the optimal hot working window is within the range of deformation temperature from 1000 to 1185 °C and strain rate from 0.01 to 0.202 s−1. Furthermore, the forging upsetting tests of the large cylindrical specimens are used to confirm the insecurity of hot deformation parameters outside the optimum hot working window. The implementation of this study can provide a theoretical basis for the determination of hot forging process parameters for 5Cr5MoSiV1 steel. [ABSTRACT FROM AUTHOR]

A new near-α titanium alloy Ti-0.3Mo-0.8Ni-2Al-1.5Zr was designed based on Ti-0.3Mo-0.8Ni (TA10). The hot compression tests were carried out at temperatures of 800–970 °C and strain rates of 0.01–5 s−1. The results show that the flow softening phenomenon in the α + β phase region is more distinct than that in the single β phase region. The Arrhenius constitutive models based on strain compensation in the α+β phase region and β phase region were established respectively, and the correlation coefficient between the predicted flow peak stress values and the experimental values reached 0.99365. The hot processing map of the alloy was established, the processing parameters of the peak efficiency: 800 ≤ T ≤ 818 °C, 0.01 ≤ ε˙ ≤ 0.0235 s−1, and 960 ≤ T ≤ 970 °C, 0.01 ≤ ε˙ ≤ 0.0213 s−1. The microstructure evolution and deformation mechanism of the compressed specimens were researched by electron backscatter diffraction (EBSD) technique. There were two nucleation mechanisms for dynamic recrystallization (DRX): sub-grains growth nucleation and high angle grain boundaries (HAGBs) bulging nucleation, the former was continuous dynamic recrystallization (CDRX), and the latter was discontinuous dynamic recrystallization (DDRX). The flow stress in the α+β phase region was softened by CDRX and dynamic recovery (DRV), while the principal deformation mechanisms in the β phase region are DRV and DDRX. The dislocation strain energy and recrystallization ability at different temperatures were quantitatively analyzed by the kernel average misorientation (KAM) and the geometrically necessary dislocation (GND), and the results showed that more complete recrystallization occurred at lower temperature in the α + β phase region. The HCP slip was principally completed by prismatic ⟨a⟩ and pyramidal ⟨c+a⟩ slip systems during the hot compression, while BCC was a mixed mode of {110}, {112} and {113} multiple slips.

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.

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

The Laasraoui segmented and Arrhenius flow stress model, dynamic recrystallization (DRX) model, grain size prediction model, and hot processing map (HPM) of Fe-Cr-Mo-Mn steels were established through isothermal compression tests. The models and HPM were proven by experiment to be highly accurate. As the deformation temperature decreased or the strain rate increased, the flow stress increased and the grain size of the Fe-Cr-Mo-Mn steel decreased, while the volume fraction of DRX (Xdrx) decreased. The optimal range of the hot processing was determined to be 1050–1200 °C/0.369–1 s−1. Zigzag-like grain boundaries (GBs) and intergranular cracks were found in the unstable region, in which the disordered martensitic structure was observed. The orderly packet martensite was formed in the general processing region, and the mixed structure with incomplete DRX grains was composed of coarse and fine grains. The microstructure in the optimum processing region was composed of DRX grains and the multistage martensite. The validity of the Laasraoui segmented flow stress model, DRX model, grain size prediction model, and HPM was verified by upsetting tests. [ABSTRACT FROM AUTHOR]

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

The two-phase titanium alloy Ti–10 V–5Al-2.5Fe-0.1 B was taken as the experimental material, and thermal compression experiments were carried out at a deformation temperature of 770–920 °C and a strain rate of 0.0005–0.5 s−1. An Arrhenius model, a modified Johnson-Cook model, and an improved BP neural network model based on the sparrow search algorithm (SSA-BP) model were established to predict the high temperature rheological stress of the alloy. A comparison of the prediction accuracy of the three models was made. When the partial random data in the rheological curves was used for model building and relatively independent data were used for predicting the rheological stress, the SSA-BP model had higher prediction accuracy, which exhibits the highest mean square correlation coefficient (R2) value of 0.9992 and the lowest root mean square error (RMSE) and average absolute relative error (AARE) values of 1.3031, and 2.0947 %, respectively. The ability of three models to predict the rheological stress for the new process parameters was verified. Results show that the SSA-BP model still has better prediction ability, which exhibits the highest mean square correlation coefficient (R2) value of 0.9720 and the lowest root mean square error (RMSE) and average absolute relative error (AARE) values of 5.0099, and 6.0382 %, respectively. The predicted values of SSA-BP for the rheological stress were used to construct the hot processing map. Results show that the trend of the power dissipation factor (η) value from the hot processing map predicted by SSA-BP can well agree with the microstructure evolution of the alloy.

The present work provides a systematical investigation on the hot deformation behavior of Fe2Ni2CrAl1.2 multi-principle element alloys (MPEAs). Hot compression tests were carried out at various temperatures ranging from 800 °C to 1100 °C at different strain rates from 0.001 s-1 to 1 s-1. The stress–strain curves obtained under different processing conditions were used to develop the constitutive model for the alloy. The advanced machine learning (ML) models including Support Vector Regression (SVR), Artificial Neural Network (ANN), Generalized Regression Neural Network (GRNN) and Random Forest (RF) were trained to predict the flow behavior of Fe2Ni2CrAl1.2 MPEAs. The predictive capability of ML algorithms were estimated, the SVR model performed better among the developed four algorithms. Then Particle Swarm Optimization (PSO) was imposed to SVR model to further enhance its prediction accuracy. The developed PSO-SVR model achieved an average testing R2 of 0.9819, as well as low RMSE and MAPE values, demonstrating its strong predictive performance. Then the PSO-SVR model was applied to generate the flow curves at various temperature and strain rate for the development of the hot processing maps. The flow instability and the optimum processing conditions were identified, indicating that instability (ζ

The thermal compression deformation behaviors of the hot extruded (HEX) FGH95 alloys were investigated systematically using the Gleeble 3800D thermal-mechanical simulator in the strain rate of 0.001~1.000 s−1 at the deformation temperature range of 1050~1120 ℃. The constitutive equations of the hot extruded FGH95 alloys were derived from the stress-strain curves obtained in the isothermal compression tests. Furthermore, the hot processing maps were established based on the dynamic models. In the results, the corresponding material constants of the constitutive equation are determined as Q=300.925 kJ·mol−1, α=0.01139 MPa−1, and n=1.86. Compared with the hot isostatic pressing (HIP) alloys, the activation energy of the hot extruded FGH95 alloys is declined by more than 50%. According to the energy dissipation efficiency and the microstructure analysis of the hot extruded FGH95 alloys, the processing safety zone and instability zone are identified during the hot extrusion process. Ultimately, the optimal processing conditions of the FGH95 alloys are proposed as the strain rate of 0.010~0.100 s−1 and the deformation temperature of 1050~1120 ℃.

It is important to explore the hot deformation behavior and establish the hot processing map of steel to design and optimize the hot rolling process. In this paper, 50CrVA spring steel was used as the experimental material. Single-pass compression tests were performed at 850–1150 °C and 0.01–5 s−1 on an MMS-300 thermo-mechanical simulation testing machine to investigate the hot deformation behavior and establish the hot processing map. The results show that as the strain rate increases and the deformation temperature decreases, the flow stress of 50CrVA spring steel increases. The constitutive equation of 50CrVA spring steel is ε˙=1.01×1014[sinh(0.0094σp)]4.53exp(−364,470RT). The dynamic recrystallization critical strain model is εc=4.19×10−3Z7.31×10−2. A hot processing map of 50CrVA spring steel was constructed to determine the plastic instability region and optimal hot working region.

The present study prepared 7075Al composites reinforced with vapor-phase-grown carbon nanofibers (VGCNFs) using the spark plasma sintering (SPS) method. Constitutive equations of the composites were calculated, and thermal processing maps were constructed by performing thermal compression tests on the VGCNF/7075Al composites at deformation temperatures ranging from 300 to 450 °C and strain rates from 0.01 to 1 s−1. This study analyzed the microstructural evolution of the VGCNF/7075Al composites during the thermomechanical processing. The experimental results demonstrated that dynamic recrystallization (DRX) primarily governed the softening mechanism of VGCNF/7075Al composites during thermomechanical processing. At high strain rates, a combination of dynamic recovery (DRV) and DRX contributed to the softening behavior. The incorporation of VGCNFs results in higher dislocation density and a larger orientation deviation within the 7075Al matrix during the thermomechanical deformation process, providing stored energy that facilitated DRX. The activation energy for deformation of VGCNF/7075Al composites was 175.98 kJ/mol. The constitutive equation of the flow stress showed that a hyperbolic sinusoidal form could effectively describe the relationship between flow stress, strain, strain rate, and temperature of VGCNF/7075Al composites. The optimal thermomechanical deformation parameters for VGCNF/7075Al composites were 400–450 °C and 0.01–0.1 s−1 when the strain ranged from 0.05 to 0.15. For strains between 0.25 and 0.35, the optimal thermomechanical parameters were 380–430 °C and 0.01–1 s−1.

The deteriorated plasticity arising from the insoluble precipitates may lead to cracks during the rolling of FeCrAl alloys. The microstructure evolution and hot deformation behavior of an FeCrAl alloy were investigated in the temperature range of 750–1200 °C and strain rate range of 0.01–10 s−1. The flow stress of the FeCrAl alloy decreased with an increasing deformation temperature and decreased strain rate during hot working. The thermal deformation activation energy was determined to be 329.49 kJ/mol based on the compression test. Then, the optimal hot working range was given based on the established hot processing maps. The hot processing map revealed four small instability zones. The optimal working range for the material was identified as follows: at a true strain of 0.69, the deformation temperature should be 1050–1200 °C, and the strain rate should be 0.01–0.4 s−1. The observation of key samples of thermally simulated compression showed that discontinuous dynamic recrystallization started to occur with the temperate above 1000 °C, leading to bended grain boundaries. When the temperature was increased to 1150 °C, the dynamic recrystallization resulted in a microstructure composed of fine and equiaxed grains. [ABSTRACT FROM AUTHOR]

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

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

In this work, the hot deformation behaviors of the high-nitrogen steel X30CrMoN15-1 from 900 °C to 1200 °C have been investigated. The microstructure observation indicates that the maximum DRXed grain size reaches 59.05 μm under the deformation temperature of 1200 °C with strain rate of 0.005 s−1, while the minimum grain size is 2.12 μm under the condition of 900 °C with strain rate of 1 s−1. The fully dynamic recrystallization (DRX) occurs at the conditions of high temperature and high strain rate (1000 °C − 1200 °C, 1 s−1 –5 s−1). There are two main mechanisms of crack formation. Under lower temperatures (900 °C-1000 °C), the significant stress concentration produced by M2(C, N) should be responsible for crack propagation along the DRXed grain boundaries. As the temperature increases to 1100 °C, the formation of cracks is mainly attributed to the uncoordinated deformation and huge pinning of dislocations by Lomer-Cottrell (L-C) locks. A new hot processing map has been established to reveals that the optimal processing domains are located at 1020 °C − 1090 °C with strain rate of 0.37 s−1 –4 s−1 and 1140 °C − 1200 °C with strain rate of 2 s−1 –5 s−1.

The hot deformation behavior of modified N50 austenitic stainless steel in the temperature range 950∼1250 °C and strain rate range of 0.01–50/s was studied by uniaxial compression experiment. The processing map and the constitutive equation for the finite element simulation were established, and the recrystallization mechanism was discussed. The results indicated that the dominant deformation mode DDRX (discontinuous dynamic recrystallization) increased with the rise of deformation temperature while the CDRX (continuous dynamic recrystallization) was on the contrary. There is a decrease in global recrystallization with increasing strain rate, up to a threshold 1/s beyond which the global recrystallization began significantly promotion owing to not only the adiabatic heat and higher stored energy, but also quick Post-DRX mechanism induced by delay quenching. The reasonable hot working interval was determined by a hot working map, then the most suitable hot extrusion parameters (1180°C-100 mm/s) were further obtained with the help of finite element simulation, and ultimately, the industrial hot extrusion trials of N50 pipes with Post-DRX features were further completed. The tensile performance of final jacket pipes was far beyond the current mainstream low-temperature austenitic structural steel and met the requirements of the new generation of superconducting coil jacket materials.

The high temperature deformation behavior and mechanisms of the cold-deformed CoCrCu1.2FeNi high-entropy alloy (HEA) were investigated by optical microscope (OM), scanning electron microscope (SEM) and electron backscattered diffraction (EBSD) at temperatures and strain rates of 950–1100 °C and 0.001–1 s−1, respectively. The results show that the flow stress increases as the deformation temperature decreases and the strain rate increases, and there is significant dynamic recrystallization (DRX) during the deformation process. 1050–1090 °C/0.02–1 s−1 and 975–1050 °C/0.002–0.2 s−1 are the optional hot temperature deformation regions. Discontinuous dynamic recrystallization (DDRX) occurs at different temperatures when the strain rate is 0.001 s−1 with a maximum recrystallization percentage of 90.28 %. The DRX degree gradually increases as the temperature rises from 950 °C to 1000 °C and from 1050 °C to 1100 °C. The maximum polar density of texture sharply increases to 11.78 at 1050 °C. The deformed microstructure leads to an increase in dislocation density, which could be effectively reduced by DRX.

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.

In order to predict the hot workability of the material more accurately, this paper takes the hot deformation of IN617B as the example. The activation energy (Q) map, Zener-Hollomon parameter (Z) map, and hot processing map were established based on the hot compression tests conducted at 950–1200 °C and 0.01–5 s−1. It was found that the area with high power dissipation values (denoted by η) in the hot processing map did not match the complete dynamic recrystallization (DRX) region completely. However, the microstructure corresponding to the high η area and low Z and Q area exhibited higher DRX. Therefore, the optimal hot processing region for this alloy was determined to be 1200 °C/0.1 s−1/0.8. Under this parameter, the DRX mechanism of IN617B alloy was dominated by discontinuous dynamic recrystallization (DDRX), supplemented by small amounts of continuous dynamic recrystallization (CDRX) and twinning dynamic recrystallization (TDRX).

Due to the high deformation resistance and poor thermal ductility of the new cast GH4151 alloy ingots, cracks are easy to occur during cogging process. For clarifying the effects of deformation parameters on microstructural evolution and dynamic recrystallization (DRX) nucleation mechanisms. In this work, the causes of crack formation and extension were first investigated using SEM and EBSD. The study revealed that the reasons for crack formation and propagation are the MC carbides at the original grain boundaries, large-size γ′ phase, residual eutectic phases, and tiny pores near the grain boundaries. Subsequently, a series of hot compression tests were performed using a Thermecamastor-Z thermo-mechanical simulator at temperatures ranging from 1080 °C to 1160 °C and a strain rate range of 0.01–10 s−1. The constitutive equation of the Arrhenius model and the hot working map was established, determining activation energy(Q) of 1086.58 kJ·mol−1. Large-size γ′ is coherent with the matrix. For the γ+γ′ dual-phase region, heterogeneous strain-induced dynamic recrystallization (HDRX) occurs, and discontinuous dynamic recrystallization (DDRX) is the main nucleation mechanism for DRX. However, for γ single-phase region, DDRX plays a more significant role. Furthermore, the MC phase (>1 μm) has different crystal orientations with the γ matrix and acts as sites for recrystallization through particle-stimulated nucleation (PSN). Finally, a fine and uniform grain structure can be obtained in the temperature range of 1120–1135 °C and the strain rate range of 0.1 s−1 to 1 s−1.

In this study, the hot processing map was drawn to study the hot formability of high strength automotive steel Docol 1500 Bor. The quenching microstructure of the test steel was observed under optical microscope and EBSD and the deformed PA (parent austenite) was reconstructed under different conditions according to KS (Kurdjumov–Sachs) OR (orientation relationship). The results indicate that the optimal deformation conditions in the stable region are strain rates less than 1s−1 and temperatures higher than 900 °C. Overall, the fine-grained martensite structure with a larger Schmid factor has a better deformation ability for subsequent service. The texture component {011} appears in the PA at the strain rate of 5 s−1 and the temperature of 1000 °C, while the dynamic recrystallization is significantly inhibited. The quenched martensite is found coarse. In the stable region, the recrystallized austenite grains with certain deformation transforms into the martensite grains with low cumulative misorientation values and higher Schmid factors. In the unstable region, the austenite grains are smaller in size, in which severe cumulative misorientation caused by higher strain rates leads to poor plasticity.

In this paper, the isothermal thermal compression simulation test of 2024 aluminum alloy was carried out. The deformation temperature is 573-723 K, the strain rate is 0.01-10 s−1, and the deformation amount is 50%. The experimental results show that the change of flow stress is inversely proportional to the deformation temperature, but directly proportional to the strain rate. OM and TEM were used to observe the microstructure after thermal deformation, the increase of temperature and the decrease of strain rate contribute to the formation of recrystallization and the decrease of dislocation density, which is the main reason for dynamic softening. The thermal deformation activation energy of 2024 aluminum alloy is 201.62 kJ/mol. The experimental peak stress constitutive model is in good agreement with the calculated value. Based on the Prasad instability model and the dynamic material model, the hot working diagram of 2024 aluminum alloy is established to construct the true strain of 50%. The ideal deformation conditions are the deformation temperature of 573-673 K and strain rate of 0.01-0.1 s−1. [ABSTRACT FROM AUTHOR]

Thermohydrogen processing (THP) is a potential method for enhancing the formability of titanium alloys. However, there has been no report on the deformation behavior and microstructure evolution of hydrogenated Ti65 alloys, which are new high-temperature titanium alloys used above 600 °C. In this study, we conducted a series of isothermal hot compression tests in the α+β and β phase field of Ti65 alloy specimens with varying hydrogen content to investigate the effect of hydrogen on high-temperature flow behavior and microstructure evolution. The results showed that after hydrogenation, the number of α phases in Ti65 alloy significantly decreased. δ hydride precipitates were observed in the specimen with 0.43 wt% hydrogen, resulting in an apparent refinement of its microstructure. Adding 0.25 wt% hydrogen reduced the deformation temperature by about 60 °C and increased deformation strain rate by nearly two orders of magnitude for Ti65 alloy. This improvement can be attributed to how hydrogen promotes dislocation movement, dynamic recrystallization (DRX), and dynamic recovery (DRV) during deformation. Similarly, as strain increases, the instability region on the hot processing map gradually decreases or even disappears due to broadening effects from added hydrogen; thus expanding its hot processing window further. This research deepens our understanding regarding deformation behavior while providing theoretical guidance for THP applications using Ti65 alloy. [Display omitted] • Effect of hydrogen on the hot deformation behavior of new Ti65 alloy was studied. • Hydrogenation significantly reduces the forming resistance and activation energy. • Hydrogen promotes dynamic recrystallization and refines the microstructure. • Hydrogen shrinks the instability region of the hot working maps. [ABSTRACT FROM AUTHOR]

The CoCrNi-based medium-entropy alloys (MEA) have been extensively investigated due to their exceptional mechanical properties at both room and cryogenic temperatures. To investigate the hot deformation behavior and the recrystallization mechanism of the CoCr0.4NiSi0.3 medium-entropy alloy, a series of deformation tests was conducted using the MMS-100 thermal simulation tester, with deformation conditions of 0.001–1 s−1/850–1150 °C. During the hot deformation process, the flow stress initially increases up to its peak value before gradually decreasing towards a steady state level. Higher flow stress levels are observed with increasing strain rate and decreasing deformation temperature. The estimated activation energy for hot deformation of this alloy is approximately 423.6602 kJ/mol. The Arrhenius-type constitutive equation is utilized to establish a modified model while incorporating power dissipation theory and the instability criterion of a dynamic material model to construct power dissipation maps and instability maps. By superimposing these maps, hot processing maps with strains of 0.4, 0.5, and 0.7 are derived. In this investigation, it is observed that regions of instability exclusively occur when the true strain exceeds 0.4. These regions of instability on the hot processing map align well with experimental findings. The suitable range of parameters for hot-working decreases as the true strain increases. The microstructure was analyzed using electron backscatter diffraction and transmission electron microscopy (TEM) techniques. The volume fraction of dynamic recrystallization (DRX) decreases with increasing strain rate but diminishes with rising temperature. The TEM characterization elucidated the mechanism of DRX in this MEA. The presence of the long-period stacking ordered (LPSO) phase was observed in both the face-centered cubic matrix and hexagonal close-packed recrystallized grains under different deformation conditions. The LPSO phase originates from the matrix at a low strain rate, whereas it is generated during recrystallization at a high strain rate. The observed increase in flow stress of the as-cast MEA is primarily attributed to the synergistic effects arising from the interaction of the dislocation with twins and the second phase. The onset of instability is effectively suppressed within a limited range through the formation of coherent second phases such as L12, LPSO, and superlattice structures resulting from phase transitions. These second phases serve as nucleation sites for recrystallization and contribute to the strengthening of dispersion. Furthermore, their interaction with dislocations and twins significantly influences both flow stress behavior and recrystallization kinetics under hot deformation. These findings not only deepen our understanding of the underlying deformation mechanisms governing MEA but also offer valuable insights for designing CoCrNi-based alloys with improved mechanical properties at elevated temperatures. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and flow stress characteristics of experimental 26CrMo7S steel were analyzed using a thermal simulator under a range of conditions, including a strain rate range of 0.01~10 s−1, a temperature range of 850~1250 °C, and a maximum deformation amount of 70%. The Arrhenius constitutive model was built for the corresponding conditions, and the model's accuracy was verified through error analysis. Additionally, hot processing maps were constructed to analyze the processing zone of the steel under different hot deformation conditions. Finally, the microstructure of the processing zones was observed and verified using the electron backscattered diffraction (EBSD). The results indicate that the interaction of work hardening and dynamic softening influences the hot deformation behavior of 26CrMo7S steel. The Arrhenius constitutive equation with a value of the correlation coefficient (r = 0.99523) accurately predicts the flow behavior of 26CrMo7S steel under different strains. The optimal processing zone obtained with the hot processing maps is within a deformation range of 1010~1190 °C and a strain rate range of 0.01~10−1.5 s−1, and the obtained microstructure is in good agreement with the analysis results. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of 40Cr/Q345B bimetal during hot compression bonding was studied using the isothermal compression method. A true stress–strain curve of the bimetal was obtained and modified to eliminate the effects of friction. The results show that the flow stress increases with decreasing deformation temperature and increasing strain rate. By analyzing the relationship of stress, deformation temperature, and strain rate, the constitutive equation of 40Cr/Q345B bimetal was obtained. The hot processing maps of 40Cr/Q345B bimetal under different strains are drawn. Through microstructure characterization, 40Cr/Q345B bimetal formed metallurgical bonding under the deformation process of this study. Combined with the hot processing map, microstructure, prior austenite grain, and microhardness distribution, it is proposed that the optimal deformation parameters of 40Cr/Q345B bimetal is 1050–1150°C and 0.02–0.4 s−1. [ABSTRACT FROM AUTHOR]

In this work, a series of isothermal hot compression tests were performed at the temperature of 900–1150 °C with the strain rate ranging from 0.01 to 10s−1 in Inconel X-750 alloy (referred as Alloy X-750). Based on the flow stress data, the back-propagation artificial neural network model was utilized to accurately predict the flow stress at elevated temperatures. Subsequently, by constructing a modified hot processing map coupled with the variation of Σ3n (n = 1, 2, and 3) twin boundaries fraction, the optimal processing parameters were determined to be in the range of 1100–1150 °C and 1-10s−1 for Alloy X-750. Moreover, the possibility of grain boundary engineering via hot deformation were also evaluated by using some critical quantification descriptors of twin related domains (TRDs), such as the number of grains in the TRDs, the lengths of the longest chain, and the average TRDs size. All the results can further verify the validity of modified hot processing map. Finally, the high-temperature flow behavior combined with the relevant microstructure characterization showed that discontinuous dynamic recrystallization is considered as the predominant softening mechanism, while the continuous dynamic recrystallization and particle-stimulated nucleation also additionally contribute to the recrystallization nucleation during the hot deformation of Alloy X-750.

Nickel-based superalloy has excellent mechanical properties at high temperature. However, the high deformation resistance, narrow deformation temperature range and complex microstructure evolution of the alloy bring great challenge to the plastic deformation of the alloy. The microstructure evolution and hot deformation behavior of as-forged nickel-based superalloy were examined through thermal compression tests at 950–1150 °C and strain rates of 0.001–10 s−1 with true strain of 1.0. The stress-strain curve exhibited a yield stage under small strain, and it comprised dynamic recovery (DRV) and dynamic recrystallization (DRX) two types. Strain rate sensitivity (m) and power dissipation efficiency (η) were calculated, and hot processing map was generated in accordance with the Murty criterion, and the rate of strain and the temperature of deformation were obtained as 1100–1150 °C and 0.02–0.4 s−1, separately, based on the optimal hot processing parameters. The instability zone was primarily in the zone of high strain rates. As the temperature of deformation was risen or the rate of strain was decreased, the DRX grain size was increased, as indicated by the microstructure results. The main deformation mechanism varied from DRX to DRV, and, then to the shear band (SB), deformation band (DB), and flow localization (FL) as η was decreased. Moreover, continuous dynamic recrystallization (CDRX) at subgrains rotation and discontinuous dynamic recrystallization (DDRX) at grain boundaries were identified during thermal deformation.

The hot workability of the 40%SiCp/Al composites (volume fraction) was studied by isothermal compression deformation on Glebble-1500D thermal simulated test machine at the deformation temperature of 350~500 ℃ under the strain rate of 0.01~10.00 s−1. The thermal deformation of the composites was analyzed according to the true stress-strain curves, and the constitutive equation was established. The strain rate sensitivity index and power dissipation efficiency factor were calculated by dynamic material model, and the power dissipation diagram, instability diagram, and two-dimensional processing map were obtained. The results show that, the strain rate and deformation temperature significantly affect the flow stress. Under the same strain rate, the flow stress decreases with the increase of deformation temperature; at the same deformation temperature, the flow stress increases with the increase of strain rate. According to the processing map, the power dissipation efficiency factor is large under the condition of high temperature and high strain rate, illustrating the microstructure transformation in the deformation region. The strain has little effect on the instability region and processing region, and the power dissipation efficiency factor increases with the increase of strain. The recommended hot working conditions for the composite is as the deformation temperature of 436~491 ℃ and the strain rate of 0.04~9.97 s−1.

The combination of wire arc additive manufacturing (WAAM) technology with traditional manufacturing process provides a promising method for fabricating the large and complex parts with the advantages of high performance, time-saving, low cost and high material utilization. In order to acquire the optimal hybrid manufacturing process, the comparative study of flow behaviors and microstructure evolution of wrought and WAAMed ultrahigh-strength (UHS) steels is carried out under the temperatures of 920–1160 o C and strain rates of 0.01–10 s - 1 . The results show that the coarse prior austenite columnar grains and carbides in the initial microstructure of the WAAMed UHS steel contribute to the higher flow stress and slower dynamic recrystallization (DRX) kinetics during hot deformation as compared to the wrought UHS steel. The hot activation energy under the peak stress of the wrought and WAAMed UHS steels is estimated to be 332.3 kJ/mol and 374.1 kJ/mol, respectively. On the basis of the hot processing maps, the common optimal processing window for WAAMed and wrought UHS steels is determined as the temperatures of 1060–1160 o C and strain rates of 0.08–0.66 s - 1 . Under these deformation parameters, the microstructures of WAAMed and wrought UHS steels consist of fine DRXed grains, and the DRX behaviors are both dominated by the discontinuous DRX and continuous DRX mechanisms. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and dynamic softening mechanism of 7B50 aluminum alloy were studied via isothermal compression experiments in the range of 320–460 °C/0.001–1.0 s−1. According to the flow curves obtained from the experiments, the flow behavior of this alloy was analyzed, and the Zener–Hollomon (Z) parameter equation was established. The hot processing maps of this alloy were developed based on the dynamic material model, and the optimal hot working region was determined to be 410–460 °C/0.01–0.001 s−1. The electron backscattered diffraction (EBSD) microstructure analysis of the deformed sample shows that the dynamic softening mechanism and microstructure evolution strongly depend on the Z parameter. Meanwhile, a correlation between the dynamic softening mechanism and the lnZ value was established. Dynamic recovery (DRV) was the only softening mechanism during isothermal compression with lnZ ≥ 20. Discontinuous dynamic recrystallization (DDRX) becomes the dominant dynamic recrystallization (DRX) mechanism under deformation conditions of 15 < lnZ < 20. Meanwhile, the size and percentage of DDRXed grains increased with decreasing lnZ values. The geometric dynamic recrystallization (GDRX) mechanism and continuous dynamic recrystallization (CDRX) mechanism coexist under deformation conditions with lnZ ≤ 15. [ABSTRACT FROM AUTHOR]