Search

The textures of the β- and α-phases of the metastable β-titanium alloy Ti5321 after hot deformation were investigated by neutron diffraction. A hot-rolled bar was solutionized in the β-phase field and then hot compressed above and below the β-transus temperature. The initial texture after full recrystallization and grain growth in the β-phase field exhibits a weak cube component {001}<100> and minor {112}<110> and {111}<110> components. After hot compression, a <100> fiber texture is observed, increasing in intensity with compression temperature. Below the β-transus temperature, dynamic recrystallization of the β-phase and dynamic spheroidization of the α-phase interact strongly. The texture of the α-phase is a <11–20> fiber texture, increasing in intensity with decreasing compression temperature. The mechanisms of texture formation during hot compression are discussed. [ABSTRACT FROM AUTHOR]

The uniaxial hot compression experiments of Mg-7Gd-3Y-0.5Zr (VW73K) alloy were carried out by using the Instron5982 mechanical testing machine with environmental box. The hot deformation behavior at 350–500 °C and 0.001–1 s−1 was studied. Based on the stress-strain curve obtained from the experiment, a strain-compensated Arrhenius constitutive model, hot processing maps, and dynamic recrystallization (DRX) kinetics model of VW73K alloy were established. The results show that the machinable area of VW73K alloy is 450–500 °C and 0.001–0.1 s−1. Under machinable parameters, the force-displacement data obtained from the experiment are highly consistent with the finite element simulation, verifying the dependability of the strain-compensated Arrhenius constitutive model for the rheological behavior of VW73K alloy during hot compression. VW73K alloy is more easily to DRX at high temperatures and low strain rates, with higher recrystallization volume fraction and faster recrystallization rate. The DRX process of VW73K alloy during hot compression is completed by the collaboration of discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX).

Magnesium alloys show great promise in high-speed transport, aerospace, and military technology; however, their widespread adoption encounters challenges attributed to limitations such as poor plasticity and strength. This study examines the high-temperature deformation of semi-solid forged AZ91D magnesium alloy through a combination of experiments and simulations, with a focus on comprehending the influence of deformation conditions on dynamic recrystallization (DRX). The findings disclose that conspicuous signs of DRX manifest in the yield stress curve as strain increases. Additionally, decreasing the strain rate and temperature correlates with a reduction in both yield stress and peak strain, and the activation energy is 156.814 kJ/mol, while the critical strain and peak strain remain relatively consistent ( ε c = 0.66208 ε p ). Microstructural changes during high-temperature deformation and the onset of DRX are thoroughly examined through experimental methods. Moreover, a critical strain model for DRX and a predictive model for the volume fraction of DRX were formulated. These equations and models, validated through a combination of experiments and simulations, serve as invaluable tools for predicting the mechanical behavior and microstructural evolution, which also establishes a foundation for accurately predicting the deformation behavior of this alloy. By analyzing the hot deformation characteristics and dynamic compression mechanism of the newly developed semi-solid forging AZ91D magnesium alloy, a numerical simulation model can be effectively established. This model objectively reflects the changes and distributions of stress, strain, and rheological velocity, providing a scientific basis for selecting subsequent plastic deformation process parameters and designing mold structures. [ABSTRACT FROM AUTHOR]

The Epoxy-based hybrid composites are attention in various engineering domains. Distinctively, natural fiber-made epoxy composites are advantageous over synthetic fiber-made composites and attracted in automotive applications such as set frames, interior panels, dashboards, etc. Moreover, due to its high moisture absorption nature, the epoxy composite formed with natural fiber is suspected to have poor adhesive quality compared to synthetic fiber composite. It leads to lower adhesive performance and limits the behaviour of composite. The prime objective of the current work is to ensure the adhesive behaviour of NaOH-treated sisal fiber (SF) epoxy composite featured with silicon carbide nanoparticles (SiC). This composite is prepared with the constant percentage of SF as 15 wt% and varied wt% of SiC through compression mould technology. Influences of treated SF and SiC on pressing behaviour of surface morphology, tensile & flexural strength, microhardness, and fracture toughness of composites are experimentally investigated with ASTM D638, D790, D4762, and D6110 policy, and its outcomes are compared to 15wt% treated SF epoxy composite. The surface morphology study confirms that the SF and SiC appearances in the epoxy matrix are uniform and homogenous. The 5wt% SiC embedded with 15wt% treated SF facilitates higher tensile (65.2 ± 1.1 MPa) & flexural strength (69.1 ± 1.3 MPa), microhardness (35.5 ± 0.5 HV), and fracture toughness (1.56 ± 0.01 MPam0.5). The enriched epoxy hybrid composite sample will recommended for automobile interior parts application. [ABSTRACT FROM AUTHOR]

The dissolution behavior of δ-ferrite in two commercial stainless steels, 15-5PH and M-154, was studied. In this work, a new approach combining hot deformation and additional post-treatment was investigated and compared with conventional annealing heat treatments for the dissolution of δ-ferrite. The results showed the acceleration in the dissolution of δ-ferrite using the new methodology. Samples from each steel were subjected to conventional annealing heat treatments at 1000 °C and 1150 °C, with soaking times of 1, 2, and 3 h. A second set of samples was subjected to hot compression experiments at 900 °C, under different strain rates, followed by post-processing heat treatments at 1000 °C and 1150 °C, while keeping the holding time constant for 10 min. Advanced microstructural characterization techniques such as Scanning Electron Microscopy (SEM), and Electron Probe Micro-Analysis (EPMA) were employed to investigate δ-ferrite dissolution in terms of changes in area fraction and chemical composition. The results indicated a strong correlation between the dissolution behavior of δ-ferrite and the processing parameters. In addition, thermodynamic calculations using Thermo-Calc software (version 2021.2.87071-368) were used to assess the diffusion of elements during the dissolution of δ-ferrite as a function of temperature and time. [ABSTRACT FROM AUTHOR]

Hybrid polymer composites are composed of fiber and filler reinforcements found to have superior specific characteristics, and it is better than monolithic polymers. The motto of the research is to enrich the properties of epoxy composite by incorporating a multi-fiber/filler combination synthesized via an advanced hot compression technique. The synthesized composites contained epoxy combinations of sisal fiber (SF), glass fiber (GF), sisal-glass fiber (SGF), and SGF with silicon carbide (SiC) are involved in X-ray diffraction (XRD) analysis, tensile/flexural strength, microhardness, and fracture toughness performance evaluation. The advanced hot compression technique has proved that better dispersion of fiber and filler in epoxy resin results in better mechanical properties. The significance of multi-fiber/filler combination (SGF-SiC) in epoxy facilitates maximum tensile, flexural, and microhardness performance and better fracture toughness behaviour of 388 ± 12 MPa, 291 ± 8 MPa, 138 ± 5 HV, and 4.7 ± 0.1 J/cm2. The enriched epoxy hybrid composite composed of SGF-SiC will be suggested for auto-aerospace cabinet applications. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Al-Zn/martensitic stainless steel particles-based composite (Al-Zn/6 %SSp), was examined in this study. The composite was tested using isothermal compression at 200–350 °C/0.01–10 s−1 and a global strain of 0.5. From the results, it was noticed that the composite’s flow stress increased with strain rate increase and drop in temperature. The constitutive equation from the hot-worked composites resulted in an estimated activation energy of 226.27 kJ/mol, which was 58 % more than that for the self-diffusion of aluminum alloy (142 kJ/mol). These findings suggest dynamic recrystallization (DRX) as the dominant deformation mechanism, as confirmed from the microstructures of the hot worked samples mostly at high temperatures and strain rates. Work hardening was predicted to dominate the deformation process by the stress exponent (n) value of 10.36 (which exceeded 5), but this was inconsistent with the microstructural observations. Comparing the linear fitting of calculated flow stress data with the estimated flow stress yielded a correlation coefficient (R2) of approximately 0.97. This observation demonstrates an effective relationship involving the calculated stress with the computed stress value for the composite material that was fabricated. Based on the processing map analysis, the instability regime occurs at 200270 °C/0.01–10 s−1. The stable domain established was at 280–340◦C/0.01–10 s−1 which is most suitable for achieving the best microstructural conditions for enhanced service performance.

This comprehensive study investigates the recrystallization behavior and deformation mechanisms of the Fe50Mn30Co10Cr10 alloy during hot compression conditions. The alloy undergoes discontinuous dynamic recrystallization, evidenced by necklace-like structures at grain boundaries, competing with the initial hexagonal close-packed (HCP) phase and γ→ε reversion. Early deformation is dominated by strain-induced martensite transformation, twinning, with slip with strain partitioning at the end of deformation. The developed Zener-Hollomon equation, validated experimentally, shows a constant activation energy of 126.96 kJ/mol. Stress-strain curves indicate that recrystallization only partially compensates for hardening effects, with no significant peaks observed. The work hardening curve exhibits significant oscillations due to encounters with pre-existing thermal HCP layers, influencing the work hardening rate. Energy efficiency maps based on temperature and strain rate identify optimal deformation conditions at temperatures ranges of 710–750 °C and strain rates of 0.0025–0.0035 s⁻1. This study provides a deeper understanding of the alloy's behavior, offering insights into the interplay between recrystallization, HCP phase formation, and twin generation. These findings contribute to the optimization of the alloy's mechanical properties for industrial applications.

This study investigates the compression deformation behavior of an Mg-Gd-Y-Nd-Zr alloy at temperatures ranging from 293 K to 573 K and strain rates ranging from 293K to 573K and strain rates ranging from 1000 s−1 to 2100 s−1 using a split Hopkinson pressure bar. A modified Johnson-Cook (JC) constitutive model and a backpropagation neural network (BPNN) model based on the improved whale optimization algorithm (IWOA) are established. Four statistical metrics, including correlation coefficient (R), mean absolute error (MAE), mean absolute percentage error (MAPE), and root mean square error (RMSE), are employed to evaluate the predictive accuracy of the two models. The findings indicate that the flow stress of the alloy is sensitive to strain, strain rate, and temperature. Increasing strain and strain rate or decreasing deformation temperature results in higher flow stress. Error calculations revealed that the modified Johnson-Cook constitutive model has an R of 0.98731, a MAPE of 7.3653%, a MAE of 19.6305 MPa, and a RMSE of 26.5704 MPa. In contrast, the model established using the IWOA-BPNN has an R of 0.99996, a MAPE of 0.58894%, a MAE of 1.2671 MPa, and a RMSE of 1.7709 MPa. The IWOA-BPNN model demonstrates higher accuracy and accurately predicts the flow stress of the alloy.

This study explores the plastic deformation mechanism and microstructural evolution of as-homogenized and as-forging Inconel 718 alloy through low temperature and slow strain rate hot compression deformation. The stress-strain curves of Inconel 718 alloy were analyzed by modulating the deformation temperature, strain rate, and strain, and the extreme grain refinement process from cast billets (with abnormally coarse grains) to the final compression sample was revealed. The results show that the true stress levels are lower during both low temperature and slow strain rate hot compression, relative to high temperature and fast strain rate deformation. For the as-homogenized Inconel 718 sample, the same grain refinement as the high temperature and fast strain rate (i.e. forging deformation) was achieved by the low temperature and slow strain rate compression deformation. For Inconel 718 samples after forging, uniform, equiaxed, fine grains with an average size of 2.9 μm are obtained at lower deformation temperatures and slower strain rates. Based on these results this low temperature and slow strain rate metallic forming process demonstrates the potential for the application of plastic deformation in controlling grain size, morphology, and distribution, providing a direct, economical, and efficient approach to achieving fine equiaxed grain structures in as-forging metallic materials.

The exploration of the relationship between process parameters and grain evolution during the thermal deformation of rare-earth magnesium alloys using simulation software has significant implications for enhancing research and development efficiency and advancing the large-scale engineering application of high-performance rare-earth magnesium alloys. Through single-pass hot compression experiments, this study obtained high-temperature flow stress curves for rare-earth magnesium alloys, analyzing the variation patterns of these curves and the softening mechanism of the materials. Drawing on physical metallurgical theories, such as the evolution of dislocation density during dynamic recrystallization, recrystallization nucleation, and grain growth, the authors of this paper establish a cellular automaton model to simulate the dynamic recrystallization process by tracking the sole internal variable—the evolution of dislocation density within cells. This model was developed through the secondary development of the DEFORM-3D finite element software. The results indicate that the model established in this study accurately simulates the evolution process of grain growth during heat treatment and the dynamic recrystallization microstructure during the thermal deformation of rare-earth magnesium alloys. The simulated results align well with relevant theories and metallographic experimental results, enabling the simulation of the dynamic recrystallization microstructure and grain size prediction during the deformation process of rare-earth magnesium alloys. [ABSTRACT FROM AUTHOR]

The evolution of microstructure during hot deformation is key to achieving good mechanical properties in aluminum alloys. We have developed a cellular automaton (CA) based model to simulate the microstructural evolution in 7075 aluminum alloy during hot deformation. Isothermal compression tests were conducted to obtain material parameters for 7075 aluminum alloy, leading to the establishment of models for dislocation density, nucleation of recrystallized grains, and grain growth. Integrating these aspects with grain topological deformation, our CA model effectively predicts flow stress, dynamic recrystallization (DRX) volume fraction, and average grain size under diverse deformation conditions. A systematic comparison was made between electron back scattered diffraction (EBSD) maps and CA model simulated under different deformation temperatures (573 to 723 K), strain rates (0.001 to 1 s−1), and strain amounts (30% to 70%). These analyses indicate that large strain, high temperature, and low strain rate facilitate dynamic recrystallization and grain refinement. The results from the CA model show good accuracy and predictive capability, with experimental error within 10%. [ABSTRACT FROM AUTHOR]

Commercial simulation software like QFORM and DEFORM do not possess adequate material data for alloys produced through powder metallurgy. Therefore, in the present study, hot compression tests of Al-5.6%Zn–2%Mg aluminum alloy were conducted at temperature ranges (300 0C-500 °C) and strain rates (0.1 s−1-0.0001 s−1). The impact of compression temperature and strain rate on the flow curve behaviour and microstructure evolution-associated mechanisms were investigated through experimentally acquired flow curves and EBSD analysis. Four constitutive models were constructed; namely the Arrhenius-type, modified Johnson Cook (MJC), modified Zerilli-Armstrong (MZA), and an artificial neural network (ANN). The results demonstrated that among the models considered, the ANN and Arrhenius-type models exhibited the lowest AARE values of 0.486 % and 3.36 %, respectively. Conversely, the MZA and MJC models displayed higher AARE values of 8.84 % and 3.93 %, respectively. Notably, the Arrhenius-type model emerged as the most suitable prediction model due to its capability to handle nonlinear relationships between factors. However, in scenarios where material properties are unknown or experimental data is limited, the MJC model can serve as a simpler alternative. The MZA model was deemed unsuitable for accurately estimating flow stress in hot compression. Remarkably, the best-trained ANN model exhibited the highest predictive performance with an AARE of 0.486 % and an R-value of 0.99. This study offers fundamental insights to improve the accuracy of simulating hot compression procedures. EBSD analysis demonstrated that higher upsetting temperatures and lower strain rates promoted recrystallization, resulting in a more uniform microstructure.

Isothermal constant strain rate compression experiments were carried out on TC20 titanium alloy using a Gleeble- 1500 thermal simulation tester to investigate its high temperature flow behaviour at deformation temperatures of 750 - 900 °C and strain rates of 0,001 - 1 s-1. The results show that the flow stress basically decreases with increasing deformation temperature and increases with increasing strain rate. The correlation coefficients and mean relative errors were 0,998 and 5,06 % respectively, proving that the BP neural network-based intrinsic structure model is effective in predicting the flow stress of the alloy.

The textures of the β- and α-phases of the metastable β-titanium alloy Ti5321 after hot deformation were investigated by neutron diffraction. A hot-rolled bar was solutionized in the β-phase field and then hot compressed above and below the β-transus temperature. The initial texture after full recrystallization and grain growth in the β-phase field exhibits a weak cube component {001} and minor {112} and {111} components. After hot compression, a fiber texture is observed, increasing in intensity with compression temperature. Below the β-transus temperature, dynamic recrystallization of the β-phase and dynamic spheroidization of the α-phase interact strongly. The texture of the α-phase is a fiber texture, increasing in intensity with decreasing compression temperature. The mechanisms of texture formation during hot compression are discussed.

Copyright of Journal of Central South University is the property of Springer Nature 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.)

This study was an attempt to combine fused deposition modelling and hot press moulding technique to fabricate hybrid polymer composites using acrylonitrile butadiene styrene (ABS) polymer, woven glass fibre (GF) and woven carbon fibre (CF). The composite specimens were subjected towere subjected to mechanical and thermal characterization.Tensile strength of GF/ABS and GF/CF/ABS composite were far higher than the virgin ABS. GF/ABS composites displayedimproved thermal resistance by giving a final residue of 42.36%, followed by GF/CF/ABS hybrid composites as per the thermogravimetric analysis. Thermomechanical analysis revealed the coefficient of thermal expansion in the order: ABS > GF/ABS > GF/CF/ABS. The entropy obtained from the DSC curve was of higher value for composites than the ABS. The ABS based composites fabricated from this technique can be applicable to structural parts in the automobiles, aircrafts, shipping vessels, etc. [ABSTRACT FROM AUTHOR]

This study investigates the hot deformation behavior and microstructural evolution of a novel medium entropy alloy subjected to low strain rates and temperatures ranging from 650 °C to 850 °C. The alloy was subjected to hot compression testing under various conditions to observe its response. At all deformation condition, discontinous dynamic recrystallization was the main restoratory mechanism. After full recrystallization, grain sizes ranged from 1 to 5 μm, accompanied by an average hardness of 250 HV. The flow curves demonstrated a typical three-stage work hardening behavior across all deformation conditions, indicative of dynamic recrystallization. It is found that the deformation activation energy (Q) exhibited a negative slope with increasing strain, with an average value of Q = 267.7 kJ/mol. Zener-Hollomon parameter was determined from the experimental results and effectively used to simulate deformation, demonstrating good agreement with experimental findings. Remarkably, following the initial cycle of recrystallization, the deformation process shifted towards grain boundary sliding instead of secondary recrystallization, displaying characteristics reminiscent of superplastic behavior. Further analysis revealed a high strain rate sensitivity (m > 0.3) at 750 °C and 850 °C, with grain sizes lower than anticipated values. In summary, this study provides a comprehensive understanding of the hot deformation behavior and microstructural evolution in the Fe50-(CoCrMnNi)50 alloy. The findings shed light on dynamic recrystallization, deformation activation energy, and the unexpected shift to grain boundary sliding. These insights are valuable for advancing the knowledge of medium entropy alloys and their potential applications in various industries.

In this paper, the microstructure evolution in an Al–Mg–Si alloy during the soaking and cooling of homogenization was investigated. Moreover, the effects of the cooling rate on the hot deformation and subsequent age-hardening behavior were studied. During the soaking, the eutectic Mg2Si is dissolved, the solute segregation is eliminated, and the Fe-bearing phase is refined. During subsequent cooling, no precipitate is formed in the water-quenched sample, while β'' and β-Mg2Si are the predominant phases formed in the air- and furnace-quenched samples, respectively. The experiments agree with the simulated continuous cooling transformation (CCT) curves. The cooling rate in homogenization has a significant effect on the flow stress when the compression is performed at 450 °C. The air-quenched sample exhibits the highest flow stress due to the formation of nanoscale β-Mg2Si particles. The effect of the cooling rate diminishes as the compression temperature increases. At a compression temperature of 500 °C, the water-quenched sample exhibits a slightly higher flow stress due to the precipitation of micrometer-scale β-Mg2Si particles and the Mg and Si solutes retained in the matrix. The compressed samples have nearly similar thermal effects and peak aging hardness increments after compression at 500 °C, indicating that the age-hardening potential of the alloys is equivalent. The same types of precipitates are formed in all compressed samples at peak aging, including the GP zone, β'', β′ and B′, where β'' is the main strengthening phase. The relationship between the precipitation behavior and the increments of hardness, electrical conductivity (EC) was analyzed.

The properties of Al alloy are significantly affected by the evolution of the microstructure during hot deformation. In this study, the 2219-O Al alloy was tested by hot compression at different temperatures, strain rates and compression ratios. Microstructures were analyzed at different parameters based on scanning electron microscopy and electron backscattered diffraction. With the temperature rising above 350 °C, more Al2Cu particles were dissolved. Instead, the increasing strain rate had a slightly positive effect on the precipitation of Al2Cu. The main dynamic recrystallization (DRX) mechanism in the 2219-O Al alloy was continuous dynamic recrystallization (CDRX) facilitated by fine Al2Cu particles. Particle stimulated nucleation (PSN) and discontinuous dynamic recrystallization (DDRX) were also observed. At 250–350 °C, the rising temperature gradually promoted the DRX with the stable content of fine Al2Cu particles. At 350–450 °C, the decrease of Al2Cu particles with rising temperature weakened the DRX. At 490 °C, all fine Al2Cu particles were dissolved, and the extremely high temperature significantly promoted the migration of grain boundaries, strengthening the DRX. The decreasing strain rate and increasing strain facilitated the DRX.

In the present paper, the effect of strain on the microstructure evolution of 7Mo-0.42N contained cast super austenitic stainless steel (SASS) during compression deformation at 1200 °C was systematically studied to optimize the hot working process. The dynamic recrystallization (DRX) grains size, recrystallization mechanism, annealing twin characteristics, and dislocation evolution during high-temperature deformation at varied strains were examined. Results show that the recrystallization behavior of the SASS during high-temperature compression can be divided into three stages. In stage I, the parent grain boundaries were gradually replaced by recrystallized grains, and observed both cyclic grain refinement and coarsening of grains. In stage II, the recrystallized grains elongated into the parent grain interior from the boundaries until the parent grain was completely covered. Meanwhile, the DRX and abnormal grain growth occurred simultaneously and developed rapidly at this stage. At stage III, the recrystallized grains abnormally grew to ∼76 μm and was deformed again because of the increased strain. The nucleation mechanism also changed during deformation. The discontinuous dynamic recrystallization (DDRX) dominated at stage I and II (ε = 0.1–0.6) with relatively low deformation strain. While in the high strain range of stage III (ε = 0.7–1.0), the continuous dynamic recrystallization (CDRX) took over. These quantitative statistics and analyses of data were carried out in terms of recrystallization grain size and nucleation mechanism under different strain variables, providing experimental basis and theoretical guidance for the production of SASS.

Magnesium alloys show great promise in high-speed transport, aerospace, and military technology; however, their widespread adoption encounters challenges attributed to limitations such as poor plasticity and strength. This study examines the high-temperature deformation of semi-solid forged AZ91D magnesium alloy through a combination of experiments and simulations, with a focus on comprehending the influence of deformation conditions on dynamic recrystallization (DRX). The findings disclose that conspicuous signs of DRX manifest in the yield stress curve as strain increases. Additionally, decreasing the strain rate and temperature correlates with a reduction in both yield stress and peak strain, and the activation energy is 156.814 kJ/mol, while the critical strain and peak strain remain relatively consistent (εc=0.66208εp). Microstructural changes during high-temperature deformation and the onset of DRX are thoroughly examined through experimental methods. Moreover, a critical strain model for DRX and a predictive model for the volume fraction of DRX were formulated. These equations and models, validated through a combination of experiments and simulations, serve as invaluable tools for predicting the mechanical behavior and microstructural evolution, which also establishes a foundation for accurately predicting the deformation behavior of this alloy. By analyzing the hot deformation characteristics and dynamic compression mechanism of the newly developed semi-solid forging AZ91D magnesium alloy, a numerical simulation model can be effectively established. This model objectively reflects the changes and distributions of stress, strain, and rheological velocity, providing a scientific basis for selecting subsequent plastic deformation process parameters and designing mold structures.

The dissolution behavior of δ-ferrite in two commercial stainless steels, 15-5PH and M-154, was studied. In this work, a new approach combining hot deformation and additional post-treatment was investigated and compared with conventional annealing heat treatments for the dissolution of δ-ferrite. The results showed the acceleration in the dissolution of δ-ferrite using the new methodology. Samples from each steel were subjected to conventional annealing heat treatments at 1000 °C and 1150 °C, with soaking times of 1, 2, and 3 h. A second set of samples was subjected to hot compression experiments at 900 °C, under different strain rates, followed by post-processing heat treatments at 1000 °C and 1150 °C, while keeping the holding time constant for 10 min. Advanced microstructural characterization techniques such as Scanning Electron Microscopy (SEM), and Electron Probe Micro-Analysis (EPMA) were employed to investigate δ-ferrite dissolution in terms of changes in area fraction and chemical composition. The results indicated a strong correlation between the dissolution behavior of δ-ferrite and the processing parameters. In addition, thermodynamic calculations using Thermo-Calc software (version 2021.2.87071-368) were used to assess the diffusion of elements during the dissolution of δ-ferrite as a function of temperature and time.

The addition of Sn improves the properties of Mg–Bi-based alloys, and can potentially overcome the high-temperature limitations of magnesium (Mg) alloys. However, high-Sn alloying leads to stress concentration during hot extrusion. Hence, in this study, the dynamic recrystallization (DRX) mechanism and hot-deformation behavior of a novel precipitate-free Mg–0.25Bi–0.25Sn alloy during hot compression conducted at 250–400 °C with strain rate of 0.001–1 s−1 were examined in detail by constructing processing maps and deriving constitutive equation. The obtained correlation coefficient was 0.99113, indicating that the proposed method can adequately predict the hot deformation behavior of the studied alloy. The calculated average activation energy was 143.0336 kJ/mol. According to the processing maps, the ideal processing areas corresponded to the conditions of 300–400 °C/0.001 s−1/1 s−1 and 400 °C/0.1 s−1. In addition, a transformation of prismatic slip to pyramidal II slip was observed at 350 °C, and the continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) processes occurred during hot compression. The classification of the dominant DRX mechanisms was based on the Zener–Hollomon parameter (Z). Under high-Z deformation conditions, CDRX and DDRX occurred simultaneously; however, CDRX was the predominant process. Under medium-Z deformation conditions, DDRX was the only DRX process. Under low-Z deformation conditions, DDRX dominated over the DRX mechanism and was partially accompanied by CDRX.

The effects of strain rates (0.001-1 s-1) on the microstructures and mechanical performance of the novel Al-Zn-Mg-Cu alloy through hot compression at 300 °C are investigated in detail. With the increase of strain rate, the dislocation density increases from 0.06 × 1013 to 3.77 × 1013m-2, which promotes the dynamic precipitation kinetics. And the volume fraction of η precipitates is calculated by the differential scanning calorimetry curves increasing from 1.36% to 3.94%. Both dislocations and precipitates promote to increase the hardness of the Al-Zn-Mg-Cu alloy. The large number of η precipitates in high-strain-rate samples hinders the recrystallization process by impeding the movement of dislocations and grain boundaries, decreasing the volume fraction of recrystallized grains to 3.1%. Continuous/discontinuous dynamic recrystallization occurs preferentially at low strain rates, and discontinuous dynamic recrystallization is rarely observed in high-strain-rate samples. In addition, because the process of continuous dynamic recrystallization promotes the transformation from low-angle grain boundaries to high-angle grain boundaries, more continuous dynamic recrystallized grains and less low-angle grain boundaries can be observed in low-strainrate samples. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of 2.5 wt.% submicron alumina reinforced magnesium composite manufactured by a new casting method was examined to assess the impact of extrusion ratio and initial microstructure on the hot workability of Mg/Al2O3 composite. The thermomechanical experiments were performed at strain rates from 0.001 s−1 to 0.05 s−1 and the temperature ranging from 523 K to 673 K. The processing map was developed using power dissipation efficiency in terms of temperature and strain rate. Results revealed that the higher extrusion ratio yields finer grain size and a more homogenous distribution of alumina particles resulting in lower flow stress and activation energy. Stable regions with more power efficiency (57%) and less instability were observed in materials that experienced higher strain. Based on the microstructural observation, dynamic recrystallization as the main restoration mechanism occurred at composite with a higher extrusion ratio and finer grains in all conditions. It was deduced that the enhanced workability of fine-grain material is confirmed by steady flow stress and safe zones of the processing map. It was also revealed that twinning–twinning intersection and flow localization are the main reasons for unstable flow in both samples with unlike grain sizes. [ABSTRACT FROM AUTHOR]

This study researched how Ce addition affects the microstructure and mechanical behavior of Cu-Fe-Ti-Mg alloys during hot compression. A thermal deformation simulation machine was used to study the hot compression process at 0.001-10 s−1 strain rates and 500-950 °C deformation temperatures. The true stress–strain curves and constitutive equations were obtained for the two alloys. Based on the electron backscatter diffraction analysis, the addition of Ce can improve the dislocation density and texture strength of the Cu-Fe-Ti-Mg alloy. The microstructure and precipitates of the Cu-Fe-Ti-Mg-Ce alloy were also analyzed. The average grain size of the Cu-Fe-Ti-Mg-Ce alloy is smaller than the Cu-Fe-Ti-Mg alloy. The addition of Ce delayed dynamic recrystallization. These findings provide a theoretical foundation for understanding the Ce addition effects on the hot deformation behavior of the Cu-Fe-Ti-Mg alloy, serving as a reference for industrial manufacturing of the alloy. [ABSTRACT FROM AUTHOR]

Quasi-beta processing was considered to be a promising processing method to obtain a component with excellent mechanical properties. To achieve an optimized quasi-beta processing parameter for TC21 alloys, the hot deformation behavior in the near β phase region for the alloy with a forged structure was investigated by the thermal compression test and finite element (FEM) simulation. The obtained results indicated that the flow behavior of the samples was significantly influenced by the hot deformation parameters, and it exhibited a flow hardening behavior at the start stage of deformation. Based on the experimental data, the constitutive equation and processing maps were obtained. The optimum hot processing parameter was 986 °C/10−3 s−1. Based on the FEM simulation results, the evolution of the temperature field, strain field, and stress field in the deformed samples at different strains exhibited a similar trend in the unstable region, which was distributed symmetrically along the center line of the samples, with the center area of the samples being the highest and the center area of the section being the lowest. [ABSTRACT FROM AUTHOR]

TiAl alloys are high-temperature structural materials with excellent comprehensive properties, and their ideal service temperature range is about 700–950 °C. High-Nb containing the Ti-46Al-8Nb-2.5V alloy was subjected to hot compression and subsequent annealing at 900 °C. During hot compression, work-hardening and strain-softening occurred. The peak stresses during compression are positively correlated with the compressive strain rates and negatively correlated with the compression temperatures. The α2 phase exhibited a typical (0001)α2 basal plane texture after hot compression, while the β0 and γ phases did not show a typical strong texture. Subsequent annealing at 900 °C of the hot-compressed samples resulted in significant phase transformations, specifically the α2 → γ and β0 → γ phase transformations. After 30 min of annealing, the volume fraction of the α2 phase decreased from 39.0% to 4.6%. The microstructure characteristics and phase fraction after 60 min of annealing were similar to those after 30 min. According to the calculation of Miller indexes and texture evolution during annealing, the α2 → γ phase transformation did not follow the Blackburn orientation relationship. Multiple crystal-oriented α2 phases with nanoscale widths (20~100 nm) precipitate within the γ phase during the annealing process, which means the occurrence of γ → α2 phase transformation. Still, the γ → α2 phase transformation follows the Blackburn orientation relationship. [ABSTRACT FROM AUTHOR]

The dynamic recrystallization (DRX) behavior and microstructure evolution of medium-Mn (0.15C–10Mn) steel were investigated through isothermal hot compression tests. The flow stress–strain curves and microstructure analysis, in wide ranges of temperatures (900–1150 °C) and strain rates (10−3 - 1 s−1), were employed to establish constitutive equations and a grain size evolution model. Since the material constants were calculated based on polynomial function of strains, strain compensation was introduced into constitutive analysis. Comparison and verification showed that the constitutive equation had a high predictive ability. The correlation coefficient and average absolute relative error were 0.99 and 4.46%, respectively, which confirm the accuracy and guidance of the model. Metallographic observation was used to implement the grain size evolution analysis of the medium-Mn steel. Microstructure evolution was characterized with a gradual increase in average recrystallized grain size and an obvious expansion in the range of grain size distribution with both deformation temperature and strain rate, which were attributed to the competition between nucleation and grain boundary migration. Besides, a grain size evolution model was established to analyze the microstructure evolution.

The exploration of the relationship between process parameters and grain evolution during the thermal deformation of rare-earth magnesium alloys using simulation software has significant implications for enhancing research and development efficiency and advancing the large-scale engineering application of high-performance rare-earth magnesium alloys. Through single-pass hot compression experiments, this study obtained high-temperature flow stress curves for rare-earth magnesium alloys, analyzing the variation patterns of these curves and the softening mechanism of the materials. Drawing on physical metallurgical theories, such as the evolution of dislocation density during dynamic recrystallization, recrystallization nucleation, and grain growth, the authors of this paper establish a cellular automaton model to simulate the dynamic recrystallization process by tracking the sole internal variable—the evolution of dislocation density within cells. This model was developed through the secondary development of the DEFORM-3D finite element software. The results indicate that the model established in this study accurately simulates the evolution process of grain growth during heat treatment and the dynamic recrystallization microstructure during the thermal deformation of rare-earth magnesium alloys. The simulated results align well with relevant theories and metallographic experimental results, enabling the simulation of the dynamic recrystallization microstructure and grain size prediction during the deformation process of rare-earth magnesium alloys.

Copyright of Journal of Central South University is the property of Springer Nature 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 hot compression of rolled 7075 alloys with different heat treatments was performed. The temperature ranged from 200 to 400 °C, and the strain rate was 0.01 s−1. The stress level decreases with the increasing temperature during compression, and the strength of the alloy in the original condition is higher than that of solution-treated (ST) alloy at the same deformation condition. The alloys with different heat treatments exhibit different anisotropic behaviors at 200 °C; the anisotropy for the alloys in both conditions becomes weaker with increasing temperature. Then, the corresponding microstructure was studied. The alloy's microstructure in its original condition consists of fiber grains; however, many equiaxed grains are found after solution treatment due to the recrystallization. The grains with different shapes lead to different anisotropic mechanical properties. For the alloys in both conditions, the density of the dislocation decreases with increasing temperature during compression, and a certain number of subgrains were found when deformed at 400 °C due to the higher driving force and a higher rate of atomic migration. Meanwhile, it is observed that the precipitates of the alloy become coarser during higher-temperature deformation. Dynamic softening is dominant in high-temperature deformation, decreasing stress during hot deformation. [ABSTRACT FROM AUTHOR]

In this study, a hybrid manufacturing technique was proposed to fabricate composites of acrylonitrile butadiene styrene (ABS) with Bidirectional woven glass fiber mat (GF)/ABS and GF/Bidirectional woven carbon fiber mat (CF)/ABS. The composites were fabricated using fused deposition modeling 3D printing, followed by hot compression molding, and their flexural, impact, and dynamic mechanical behaviors were examined. Results indicated that composites with GF and ABS combinations had shown the highest maximum flexural strength (64.46 MPa) and impact strength (0.089 J/mm2). The hybrid composites showed intermediate performance between ABS and GF/ABS composites, with higher flexural strain before failure than ABS and GF/ABS. A comprehensive analysis utilizing scanning electron microscopy was carried out to evaluate the adhesion characteristics of the fiber‐matrix interface in impact‐tested samples. Dynamic mechanical analysis showed that GF/ABS composites had offered superior E′, E″, and tanδ than the hybrid configuration. The peak tan delta values obtained from ABS, GF/ABS, and GF/CF/ABS composites were utilized to determine their respective glass transition temperatures. The observed values for ABS, GF/ABS, and GF/CF/ABS composites were 109.65, 69.95, and 71.5°C, respectively. Some potential applications for the composites fabricated in this study could include the development of lightweight and strong components for aerospace or automotive industries. [ABSTRACT FROM AUTHOR]

The hot compression tests of medium carbon V and V–Ti microalloyed steels are carried out at the temperature of 900–1100 °C and strain rate of 0.01–10 s−1. Three physical constitutive models based on creep theory are studied, the prediction accuracy is compared and analyzed by employing the correlation coefficient (R) and average absolute relative error (AARE), and the deformation/diffusion mechanisms are discussed. The results show that Ti has obvious hardening effect in V microalloyed steel and retards the onset of dynamic recrystallization. The physical constitutive model containing the theoretical value of creep exponent 5 can accurately describe the hot flow behavior of both steels, the prediction accuracy of which is comparable to that of the model containing exponent n, reflecting that the dominant deformation mechanism of both steels is dislocation climbing. Furthermore, a modified physical constitutive model combining diffusion mechanisms of lattice diffusion and grain boundary diffusion shows higher accuracy (R = 0.996, AARE = 3.81% of V steel and R = 0.994, AARE = 4.52% of V–Ti steel), indicating that the diffusion mechanism is controlled not only by lattice diffusion but also by grain boundary diffusion. [ABSTRACT FROM AUTHOR]

Through isothermal hot compression experiments at various strain rates and temperatures, the thermal deformation behavior of Zn-2.0Cu-0.15Ti alloy is investigated. The Arrhenius-type model is utilized to forecast flow stress behavior. Results show that the Arrhenius-type model accurately reflects the flow behavior in the entire processing region. The dynamic material model (DMM) reveals that the optimal processing region for the hot processing of Zn-2.0Cu-0.15Ti alloy has a maximum efficiency of about 35%, in the temperatures range (493–543 K) and a strain rate range (0.01–0.1 s−1). Microstructure analysis demonstrates that the primary dynamic softening mechanism of Zn-2.0Cu-0.15Ti alloy after hot compression is significantly influenced by temperature and strain rate. At low temperature (423 K) and low strain rate (0.1 s−1), the interaction of dislocations is the primary mechanism for the softening Zn-2.0Cu-0.15Ti alloys. At a strain rate of 1 s−1, the primary mechanism changes to continuous dynamic recrystallization (CDRX). Discontinuous dynamic recrystallization (DDRX) occurs when Zn-2.0Cu-0.15Ti alloy is deformed under the conditions of 523 K/0.1 s−1, while twinning dynamic recrystallization (TDRX) and CDRX are observed when the strain rate is 10 s−1. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of a novel Al–Cu–Li alloy is investigated by isothermal compression with a temperature range of 350–510 °C and a strain rate range of 0.001–10 s−1. Constitutive analysis and hot processing maps are used to analyze the influence of deformation parameters on hot deformation behavior, and the related microstructure evolution is characterized by scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM) observations. The results indicate that the microstructure evolution of the alloy during deformation was dominated by dislocation movement and substructure evolution. With the increase in temperature or the decrease in strain rate, the dislocations introduced by deformation gradually transform into dislocation walls and substructures, showing distinct dynamic recovery (DRV) and slight dynamic recrystallization (DRX) characteristics. The degree of DRX is very low, while it is more sensitive to strain rate than temperature. According to the analysis of hot processing maps and microstructure, the optimum deformation temperature and strain rate of the alloy are determined as at least 430 °C and 0.008–0.15 s−1, respectively. These results can be referable for the industrial thermomechanical processing of this novel Al–Cu–Li alloy. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Mg-9.16Gd-3.03Y-1.44Zn-0.61Zr alloy was examined by hot compression experiments at 623–753 K with strain rates 0.1–20 s−1. Flow stress-strain curves developed an Arrhenius-type equation with adjustment for strain. The influence of strain on microstructure evolution was studied by optical microscope. The results showed that with the increase of deformation, LPSO phase broken and kinked and interacted with dislocations to promote nucleation of dynamic recrystallization (DRX) grains. In addition, the effects of temperature and strain rate on DRX during hot compression were examined using electron back-scatter diffraction. The results demonstrated that the volume fraction of DRX grains improved as temperature and strain rate increased. The alloys could adapt to plastic deformation caused mostly by continuous and discontinuous dynamic recrystallization. Transmission electron microscopy was then utilized to observe the phase structure. The dynamic precipitates occurred after hot compression, and the LPSO phase was broken and kinked, which coordinated the plastic deformation. Using the Avrami equation, the DRX dynamic model of the alloy at 0.1 s−1 was established for the first time.

Two-phase titanium alloy Ti–6Al–2Sn–4Zr–6Mo (TC19) has an excellent application prospect in aerospace field. In order to study its hot deformation behavior and the microstructure evolution mechanism of TC19 titanium alloy, hot compression tests were carried out. The flow behavior of this alloy was predicted by the constitutive models. Besides, the hot processing map of TC19 alloy was drawn according to the dynamic material model (DMM) theory. The peak efficiency of energy dissipation region occurred in the temperature range of 850–1000 °C with the strain rate of 0.001–0.1 s−1. The main deformation mechanisms were dynamic recovery (DRV) and dynamic recrystallization (DRX). It seems that the region of deformation instability was concentrated in high strain rate. The main deformation mechanisms in the structure were deformation band (DB), flow localization (FL), and recrystallized grains produced by continuous dynamic recrystallization (CDRX). Deformation mechanism of TC19 alloy was mainly controlled by the deformation rate. When the deformation rate was low, the deformation mechanism was mainly DRV and the strain-induced grain boundary migration, which led to the bulging of the grain boundary and resulted in discontinuous dynamic recrystallization (DDRX) with the increasing deformation rate. Furthermore, the sub-grain rotated continuously to transform from low angle grain boundaries (LAGBs) into high angle grain boundaries (HAGBs) at the high deformation rate continuously. Recrystallized grains packed with HAGBs were observed in the microstructure. The existence of ω phase in the precipitated phase observed by diffraction pattern, which indicated that phase transition was related to the deformation rate.

In this work, the hot processing maps of CF170 maraging stainless steel were generated by using flow stress data obtained from an isothermal compression experiment on the Gleeble-3800 hot compression simulator. The microstructure corresponding to the stable regions in the hot processing map was observed with an optical microscope. The results showed that the steel is susceptible to deformation temperature, strain, and strain rate, and the optimal hot working parameter is a strain rate range of 0.01?0.1 s?1 and a temperature range of 1350?1373K when the strain is 0.6. In addition, the texture evolution of prior austenite during hot compression was investigated based on reconstructing a parent grain by Electron Back-Scattered Diffraction. The results showed that twinning-induced dynamic recrystallization is another mechanism except for strain-induced dynamic recrystallization at a higher strain rate. Further, the deformed microstructure with a Cube texture (1 0 0) ©0 1 0ª will preferentially nucleate, and the increase in temperature makes the Cube texture (1 0 0) ©0 1 0ª change to the rotated Cube texture (1 0 0) ©1 1 0ª, and the increase of strain rate inhibits the growth of recrystallized grains and weakens texture. [ABSTRACT FROM AUTHOR]

The flow curves of Al-7.8Zn-1.65Mg-2.0Cu (wt.%) alloy in the temperature range of 300-450 °C and strain rate range of 0.01-10 s−1 were obtained by hot compression tests on a Gleeble-3500 isothermal simulator. The effects of deformation heat-induced temperature rising and friction on the flow curves were discussed and the flow curves were corrected to exclude these influences. The constitutive model was constructed and its accuracy was evaluated by the correlation coefficient (R) and average absolute relative error. The values of the corresponding evaluators were determined to be 0.9841 and 6.2346%, respectively. The processing maps were developed and through which the optimal hot working window for this alloy was determined in the range of 380-450 °C and 0.01-0.368 s−1. The microstructure evolution observations revealed that micro-crack and flow localization occurred at 300 °C and 10 s−1 and 400 °C and 10 s−1, which located in the instability region of processing map. With the increasing strain rate, the deformation activation energy decreased, simultaneously, the dislocation multiplication rate accelerated, which resulted in pronounced increasing of LAGBs and HAGBs. [ABSTRACT FROM AUTHOR]

To solve the problem of insufficient predictability in the classical models for the Ti6242s alloy, a new constitutive model was proposed, based on the partial derivatives from experimental data and the Taylor series. Firstly, hot compression experiments on the Ti6242s alloy at different temperatures and different strain rates were carried out, and the Arrhenius model and Hensel–Spittel model were constructed. Secondly, the partial derivatives of logarithmic stress with respect to temperature and logarithmic strain rate at low, medium and high strain levels were analyzed. Thirdly, two new constitutive models with first- and second-order approximation were proposed to meet the requirements of high precision. In this new model, by analyzing the high-order differential data of experimental data and combining the Taylor series theory, the minimum number of terms that can accurately approximate the experimental rheological data was found, thereby achieving an accurate prediction of flow stress with minimal material parameters. In the new model, by analyzing the high-order differential of the experimental data and combining the theory of the Taylor series, the minimum number of terms that can accurately approximate the experimental rheological data was found, thereby achieving an accurate prediction of flow stress with minimal material parameters. Finally, the prediction accuracies for the classical model and the new model were compared, and the predictabilities for the classical models and the new model were proved by mathematical means. The results show that the prediction accuracies of the Arrhenius model and the Hensel–Spittel model are low in the single-phase region and high in the two-phase region. In addition, second-order approximation is required between the logarithmic stress and logarithmic strain rate, and first-order approximation is required between logarithmic stress and temperature to establish a high-precision model. The order of prediction accuracy of the four models from high to low is the quadratic model, Arrhenius model, linear model and HS model. The prediction accuracy of the quadratic model in all temperatures and strain rates had no significant difference, and was higher than the other models. The quadratic model can greatly improve prediction accuracy without significantly increasing the material parameters. [ABSTRACT FROM AUTHOR]