Arrhenius-type Constitutive Equation Research Articles

Thermo-mechanical processing characteristics and strain-rate-sensitive degradation properties of Mg-Er-Ni alloys

Hot deformation behavior, the corresponding microstructure evolution, and degradation properties of a weak-textured Mg-Er-Ni alloy containing a high-volume fraction of Ni-LPSO phases, have been investigated. Hot deformation behavior has been carried out in the temperatures range of 370 ∼ 460 °C and strain rates range of 0.001 ∼ 1 s−1. Flow stress-strain curves of high strain rate cases show a continuous increase trend without a steady or a peak stage, while that of low strain rate cases show an obvious dynamic softening after peak stress. Based on flow stress-strain curves, materials constants calculated by an Arrhenius-type constitutive equation, show a high n and Q compared to those of high-volume fraction α-Mg matrix Mg alloys. Optimal processing windows, based on the dynamic material model, is determined as high temperature domains. As for microstructure evolution, a complete recrystallization and dispersive Ni-LPSO fragments for high temperature & low strain rates while a restricted recrystallization and a streamline distribution LPSO phase for high temperature & high strain rates are observed. Varying degrees of continuous dynamic recrystallization, particle induced nucleation mechanism, as well as coordinated deformation of LPSO through kinking and bending account for the strain-rate-dependence hot deformation mechanism. As a result, dispersive Ni-LPSO fragments at low strain rates provide more degradation channels for the α-Mg matrix and thus possess better a degradation rate than the streamlined LPSO at high strain rates.

Hot deformation and dynamic recrystallization of Mg-Gd-Y-Zn-Zr alloy containing high volume fraction 18R-LPSO phase

The deformation behavior including flow behavior, hot workability and dynamic recrystallization (DRX) mechanism of as-cast Mg-9Gd-3Y-3.75Zn-0.6Zr alloy containing 26.5 % volume fraction 18R long-period stacking ordered (LPSO) phase distributed in continuous network morphology were studied by hot compression experiments at deformation condition of 350 ℃-500 ℃, 0.01–1 s−1 strain rate and 0.75 true strain. The influence of deformation conditions on the microstructural evolution was analyzed by using optical microscopy (OM), scanning electron microscope (SEM), electron back scatter diffraction (EBSD) and transmission electron microscope (TEM). Results display that stress exponent and deformation activation energy are 5.58 and 241.39 kJ·mol−1 correspondingly, which suggested that dislocation climb is the principal deformation mechanism. The Arrhenius type constitutive equation is established as ε̇=4.09×1016sinh(9.922×10−3σ)5.58exp(−241394RT). Microstructure evolution can be characterized by Zener-Holomon parameter (Z) which reflects the combining effect of temperature and strain rate on microstructure. At low lnZ (lnZ<36), the 18R-LPSO phase dissolves from continuous network to blocks and high DRX volume (>50 %) is realized by particle-stimulated nucleation and discontinuous dynamic recrystallization. At moderate lnZ (36≤lnZ<40), a fine and coarse grains bimodal structure is formed at the original grain boundary by continuous dynamic recrystallization resulting in a DRX volume between 10 % and 50 %. At high lnZ (lnZ≥40), layered 14H‐LPSO phase precipitates and inhibits DRX (DRX volume＜10 %) by absorbing dislocations. With combination of dissipation coefficient, instability factor and microstructure analysis, 400 ℃/0.01–0.05 s−1 and 450 ℃/0.01 s−1 are confirmed as optimal hot working domains for the as-cast alloy, under which conditions bimodal microstructure and equiaxed grains microstructure (average grain size 10.3 μm) can be formed correspondingly.

Study on the influence of κ-carbide on the high temperature flow behavior of the medium-Mn lightweight steel: Modeling and characterization

Isothermal compression tests were carried out on the Fe-11Mn-10Al-0.9C medium-Mn lightweight steel in the temperature range from 800 °C to 1100 °C and strain rate range from 0.001 s−1 to 10 s−1 to investigate the influence of κ-carbide on the hot flow behavior. The true stress-true strain curves were analyzed to evaluate the role of κ-carbide on the softening phenomena during straining. It's found flow stress drops more remarkably from the peak point to the end of deformation at low temperature and low strain rate, that condition is favorable for the precipitation of κ-carbide instead of the occurrence of DRX. The activation energy of hot deformation based on the peak stress was calculated as 454.517 kJ mol−1, but this typical strain-compensated Arrhenius-type constitutive equation was found inappropriate to model the flow behavior of the present steel, especially at the low temperature regime. By comparison, a physically-based constitutive model consisting of Bergström's equation (ε<εp) and Kolmogorov-Johnson-Mehl-Avrami's equation (ε>εp) was developed and could predict the flow behavior of the steel accurately. Electron backscattered diffraction (EBSD) analysis revealed the formation of necklace structure at high strain rate and the dynamic recrystallization (DRX) proceeded more adequately with the decrease in strain rate and increase in the deformation temperature. The precipitation of κ-carbides in both austenite grain interior and boundaries (GI and GBs) were enhanced at relatively low deformation temperature (e.g., 800 °C) and greatly improved the peak stress by hindering the dislocation motion. With the increase of deformation, the GB κ-carbide gradually coarsened and induced the decomposition of deformed austenite via the eutectoid reaction (γ→α+κ) at lower strain rate (e.g., 0.001 s−1) due to the sufficient transformation time, consequently leading to the remarkable flow stress softening. The microstructure characterization result was in agreement with variations of parameters (i.e., U, Ω, ρp and nA) with different deformation condition.

High-temperature deformation behavior and microstructural evolution of TC17 alloy

The hot deformation behavior and microstructure evolution of TC17 alloy were investigated by hot compression tests at 700–950 ℃ with strain of 0.9 and strain rate of 0.001–10 s-1. A modified Arrhenius-type constitutive equation was established to describe the hot deformation characteristics. The spheroidization process of α phase was studied by scanning electron microscopy. The results show that the lamellar α phase forms a groove through the boundary splitting mechanism, and the gradually deepened groove eventually leads to the splitting of the lamellar α phase, and then diffuses to the surrounding under the termination migration mechanism. Finally, the lamellar α phase spheroidizes. The microstructure evolution during hot compression was analyzed by electron backscatter diffraction technique. The results show that the spheroidization of lamellar α phase is the main softening mechanism of TC17 alloy at low temperature. With the increase of temperature, dynamic recrystallization gradually transforms into the main softening mechanism of TC17 alloy. At the same time, the discontinuous dynamic recrystallization at the subgrain boundary and the continuous dynamic recrystallization at the subgrain rotation of TC17 alloy were found.

Hot deformation behaviors and microstructure evolution of a supersaturated nickel-based superalloy

The hot deformation behaviors and microstructure evolution of a supersaturated Ni-based superalloy GH4742 were investigated by isothermal compression tests. The deformation temperature range encompassed γ' sub-solvus (1000–1075 °C) and super-solvus (1100–1150 °C), with strain rates ranging from 0.001 s−1 to 1 s−1. Separate Arrhenius-type constitutive equations were established considering the re-precipitation of the γ' phase. The correlation coefficient between the calculated stresses and the experimental data was as high as 0.997, which indicated that the rheological behaviors of the material during hot deformation processes could be accurately analyzed by the constitutive relationship. Additionally, the activation energies for the γ + γ' two-phase region and the γ single region were calculated to be 949.08 kJ.mol−1 and 437.66 kJ.mol−1, respectively. Microstructural analysis revealed that the partial dynamic recrystallisation (DRX) occurred in the γ' sub-solvus regime whereas the full DRX occurred in the γ' super-solvus regime. The low DRX fractions in the γ' sub-solvus regime were attributed to the presence of near-spherical re-precipitated γ' phase, which effectively suppresses the nucleation and growth of new grains. The deformed grains were oriented in the <101> direction parallel to the compression direction. Meanwhile, the non-monotonic relationship between the degrees of DRX and strain rate was observed due to the adiabatic temperature rise. The retarding effects of solute elements on the grain growth in the γ' super-solvus regime were determined by comparing the recrystallized grain sizes from theoretical analysis and experiment values. This work can provide guidance for understanding the deformation behaviors of the alloy and achieving desired microstructures.

Enhancing flow stress predictions in CoCrFeNiV high entropy alloy with conventional and machine learning techniques

A machine learning technique leveraging artificial intelligence (AI) has emerged as a promising tool for expediting the exploration and design of novel high entropy alloys (HEAs) while predicting their mechanical properties at both room and elevated temperatures. In this paper, we predict the flow stress of hot-compressed CoCrFeNiV HEAs using conventional (qualitative and quantitative models) and advanced machine learning approaches across various temperature and strain rate conditions. Conventional modeling methods, including the modified Johnson-Cook (JC), modified Zerilli–Armstrong (ZA), and Arrhenius-type constitutive equations, are employed. Simultaneously, machine learning models are utilized to forecast flow stress under different hot working conditions. The performance of both conventional and machine learning models is evaluated using metrics such as coefficient of determination (R2), mean abosolute error (MAE), and root mean squared error (RMSE). The analysis reveals that the gradient boosting machine learning model shows superior prediction accuracy (with value R2 = 0.994, MAE = 7.77%, and RMSE = 9.7%) compared to conventional models and other machine learning approaches.

Hot deformation behavior and microstructure evolution of TC11 dual-phase titanium alloy

Thermomechanical processing is one of the major steps in the fabrication of structural components used in various engineering applications. The thermomechanical coupling effect of temperature and strain rate has a significant impact on the stress-strain thermal deformation behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) alloy. Here, the hot deformation behavior of TC11 dual-phase alloy has been comprehensively investigated by the hot compression tests with deformation temperatures ranging from 870 °C to 960 °C and strain rates of 0.01 s−1 to 1 s−1. Based on the flow stress curves and Arrhenius-type constitutive equation, a strain compensated Arrhenius model for TC11 alloy was successfully developed, achieving rapid and accurate prediction of high-temperature flow stress. By studying the deformed microstructure characteristics of materials under various deformation conditions, the role of deformation temperatures and strain rates was fully discussed in microstructure evolution, including the primary α phase (αp) and lamellar (αs). The thin-long lamellar shape αs can be obtained at a higher strain rate and deformation temperature. The predominance of single-peaked stress features in most flow curves, along with EBSD characterization results, indicates that continuous dynamic recrystallization (DRX) is the primary softening mechanism under different deformation conditions. This work supports the rapid prediction of flow stress and the relationship between process parameters and microstructural evolution to expedite the design optimization of plastic deformation process parameters and the development of advanced TC11 titanium alloy with targeted microstructures.

Hot Deformation Behavior and Microstructure Evolution of Al-7.92 Zn-1.64 Mg-2.00 Cu Alloy

During the thermal deformation of aluminum alloy materials, the deformation conditions such as deformation volume, temperature and strain rate are important factors that influence the deformation mechanisms such as work hardening, dynamic recovery and dynamic recrystallization. Under the interaction of different deformation mechanisms, the properties of aluminum alloy materials will change significantly. In this study, isothermal hot compression experiments were conducted on the Al-7.92 Zn-1.64 Mg-2.00 Cu alloy to analyze its hot flow behavior (T = 250~450 °C, ɛ̇ = 0.001~1 s−1). The obtained flow behavior data were used to construct an Arrhenius-type constitutive equation and processing maps, investigating organizational evolution under diverse hot deformation conditions. The results show that the energy dissipation rate can reach 0.37 when the deformation temperature T = 380~450 °C and the strain rate ɛ̇ &lt; 0.1 s−1, suggesting that the material is most suitable for thermal deformation processing at high temperatures and low strain rates. At a strain rate of 0.1 s−1 and a temperature of 450 °C, the percentage of recrystallized grains and substructures increased by 7.20% and 3.14%, respectively, compared to 300 °C, which is due to the severe dynamic recovery and dynamic recrystallization. At 350 °C and 0.1 s−1, there was a higher percentage of recrystallized grains and substructures, 5.44% and 5.87% higher, respectively, than at a strain rate of 1 s−1, indicating that the release of dislocation accumulation due to deformation storage energy will be more favored at low strain rates, which promotes the enhancement of the dynamic recrystallization mechanism.

Investigation of the Hot Deformation Behavior and Mechanism of a Medium-Entropy CoCr0.4NiSi0.3 Alloy

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.

Constitutive model for hot deformation behaviors of Al/Cu bimetal composites based on their components

The hot deformation behavior of Al/Cu bimetal composites was investigated using isothermal compression tests at temperatures of 400–500 °C and strain rates of 0.001–0.1 s−1 by considering the effects of volume fractions of composite components (30%–51% Al). In this regard, new proper constitutive equations were developed using Arrhenius-type and the rule of mixture (ROM) models. Experimental flow stress (FS) showed that processing parameters and volume fraction affect the flow behavior of composite as the volume fraction of copper has a more substantial impact on the flow behavior of the composite rods at elevated temperatures. The values of correlation coefficient (r) and average relative error of the developed Arrhenius-type constitutive equation and ROM model were 0.9826, 0.9742 and 0.9718, and also 0.18%, 1.69% and –0.84% for volume fractions of 51%, 42% and 30% Al, respectively. The results indicate that the newly developed constitutive model can successfully predict the hot working behavior of the considered bimetal composite. Finally, the microstructure of composites was investigated under different processing conditions. The dominant mechanisms for three considered volume fractions were identified at different temperatures, strains, and strain rates specified for the hot deformation of the Al/Cu composite.

The Portevin-Le Chatelier Effect of Cu-2.0Be Alloy during Hot Compression.

The Portevin-Le Chatelier effect of Cu-2.0Be alloy was investigated using hot isothermal compression at varying strain rates (0.01-10 s-1) and temperature (903-1063 K). An Arrhenius-type constitutive equation was developed, and the average activation was determined. Both strain-rate-sensitive and temperature-sensitive serrations were identified. The stress-strain curve exhibited three types of serrations: type A at high strain rates, type B (mixed A + B) at medium strain rates, and type C at low strain rates. The serration mechanism is mainly affected by the interaction between the velocity of solute atom diffusion and movable dislocations. As the strain rate increases, the dislocations outpace the diffusion speed of the solute atoms, limiting their ability to effectively pin the dislocations, resulting in lower dislocation density and serration amplitude. Moreover, the dynamic phase transformation triggers the formation of nanoscale dispersive β phases, which impede dislocation and cause a rapid increase in the effective stress required for unpinning, leading to the formation of mixed A + B serrations at 1 s-1.

Analysis of residual stress relief for Ti62A alloy welded joints by post weld heat treatment considering creep effect

In this paper, the Arrhenius-type constitutive equation based on strain compensation was developed, and the constants of the constitutive equation were determined by linear fitting to construct the material models of Ti62A alloy. Meanwhile, the creep parameters of Ti62A alloy at high temperature were corrected by existing experiments, and the Norton creep model during post weld heat treatment (PWHT) was established. The sequential coupling finite element method was used to calculate the residual stress distribution in the welding and PWHT processes of Ti62A alloy plates. The effects of PWHT parameters on the residual stress relief of welded joints were revealed, such as creep, heating rate, and heat treatment temperature. The results reveal that the creep has an important influence on residual stress relief during PWHT. Compared with longitudinal residual stress, the effects of heating rate and heat treatment temperature on transverse residual stress are more significant. A lower heating rate or higher heat treatment temperature will be beneficial for releasing residual stress. The results of this paper will contribute to a better understanding of PWHT mechanisms and provide a good theoretical guidance for optimizing process parameters.

Hot deformation behavior of a novel Ni–W–Co high-density Ni-based alloy with ultra-high W content

Ni–W–Co alloy is a recently developed single-phase Ni-based alloy with high density. An ultra-high content of W (35–38 wt%) is essential to ensure the high density but unfavorable to possess outstanding ductility or present large deformation. In this study, the flow stress behavior and hot workability of Ni–W–Co alloy were investigated through simulated compression tests with a temperature range of 1000–1300 °C and strain rate range of 0.01–5 s−1. The Arrhenius-type constitutive equation at peak stress was established. The constitutive equation displays prediction bias due to the lower experimental values at low temperature and high strain rate. The ultra-high solution content of W not only results in the severely inhibited discontinuous dynamic recrystallization (DDRX) and high apparent deformation activation energy (568.5 kJ/mol) but also promotes the generation of subgrain boundaries. Furthermore, continuous dynamic recrystallization (CDRX) occurs during deformation at a low temperature and a high strain rate, which is quite different from the Ni-based alloy with a low W content that only DDRX occurs. The activation of CDRX shortens the stage at which work hardening dominates, and results in lower peak stress values. The prediction bias of the constitutive equation caused by the lower peak stress was eliminated through difference compensation. The hot processing maps at strain values of 0.3, 0.5, 0.7, and 0.9 were constructed. The optimal hot processing parameters of the Ni–W–Co alloy, which aims to obtain full recrystallization microstructure without defects, are strain rate 0.01–0.1 s−1 and temperature 1225–1300 °C in combination with the hot processing maps and microstructure evolution. This study provides a reference for the hot processing and microstructural modification of the novel Ni–W–Co alloy with an ultra-high W content.

Constitutive model and processing maps of 7055 aluminum alloy used for fasteners

The hot deformation behavior of an annealed 7055 aluminum alloy was investigated by isothermal compression tests over the temperatures range of 250–450 °C and strain rates range of 0.001–10 s−1. The true stress-strain curves were obtained by applying friction and temperature corrections to experimental data. Based on the corrected curves, a sixth-order polynomial Arrhenius-type constitutive equation is established to represent the material characteristic constants. To investigate the workability of this material, processing maps representing the power dissipation capacity with examining various strains were created. According to the processing maps and examination of microstructures, the recommended processing parameters were within the temperatures range of 300–400 ℃ and strain rates range of 10−1.5-1 s−1, a good workability and uniformly deformed grains can be obtained under this condition. The preponderant softening mechanism is DRV (dynamic recovery) over all the recommended deformation parameter domains, but the effect of DRX (dynamic recrystallization) is enhanced in regions of low strain rate and high temperature deformation.

Hot deformation behavior of a novel alpha + beta titanium alloy TIMETAL®407

The hot deformation behavior of a newly developed α + β titanium alloy TIMETAL®407 (Ti407) was characterized in starting transformed-β microstructure at different temperatures (T = 650–950 °C) and strain rates (ε̇ = 10−3 - 1 s−1) using hot-compression testing. The Arrhenius type constitutive equations are developed for Ti407 and the activation energy for deformation is determined as 333.1 and 179.8 kJ/mol in the α and β dominated phases, respectively. The processing and strain-rate sensitivity maps of Ti407 were generated at true strain, ε = 0.5 on the basis of modified dynamic materials model (DMM) proposed by Murty and Rao. Results obtained from the maps and microstructural analysis of the deformed specimens indicates three distinct stable domains (I-A, II-A and I-B) within the examined conditions. Out of the three stable domains, Domain I-A occurring in the α + β phase field (T = 800–860 °C and ε̇= 6.3 ×10−2 - 1 s−1) and Domain I-B in the β phase field (T = 900–950 °C and ε̇= 10−3 - 1 s−1) were optimum domains for possible hot working of Ti407. The peak in the efficiency of power dissipation of about 58% occurred in Domain I-A at 850 °C/1 s−1, where dynamic spherodization of α lamellae occurred. In Domain I-B, formation of fine dynamically recrystallized β grains was observed with peak in power dissipation efficiency of about 60% at 950 °C/10−3 s−1. Ti407 showed evidence of flow instabilities like flow localization and kinking of α lamellae in the predicted unstable zones identified from the processing map. The hot workability of Ti407 on the basis of expanding or shrinking stable regimes for processing is also compared with CP-Ti and Ti-6Al-4V alloys at identical strain rates and temperatures relative to the beta-transus. Finite element method (FEM) software DEFORM®− 3D was used for forging simulation at the peak in deformation efficiency condition in various stable domains to evaluate the flow response and distributions of stress/strain in the forged billets.

Flow Stress Modeling of Tube and Slab Route Sheets of Zircaloy-4 Using Machine Learning Techniques and Arrhenius Type Constitutive Equations

Flow Stress Modeling of Tube and Slab Route Sheets of Zircaloy-4 Using Machine Learning Techniques and Arrhenius Type Constitutive Equations

Flow Behavior of AA5005 Alloy at High Temperature and Low Strain Rate Based on Arrhenius-Type Equation and Back Propagation Artificial Neural Network (BP-ANN) Model.

To realize the purpose of energy saving, materials with high weight are replaced by low-weight materials with eligible mechanical properties in all kinds of fields. Therefore, conducting research works on lightweight materials under specified work conditions is extremely important and profound. To understand the relationship of aluminum alloy AA5005 among flow stress, true strain, strain rate, and deformation temperature, hot isothermal tensile tests were conducted within the strain rate range 0.0003–0.03 s−1 and temperature range 633–773 K. Based on the true stress-true strain curves obtained from the experiment, a traditional constitutive regression Arrhenius-type equation was utilized to regress flow behaviors. Meanwhile, the Arrhenius-type equation was optimized by a sixth-order polynomial function for compensating strain. Thereafter, a back propagation artificial neural network (BP-ANN) model based on supervised machine learning was also employed to regress and predict flow stress in diverse deform conditions. Ultimately, by introducing statistical analyses correlation coefficient (R2), average absolute relative error (AARE), and relative error () to the comparative study, it was found that the Arrhenius-type equation will lose accuracy in cases of high stress. Additionally, owning higher R2, lower AARE, and more concentrative value distribution, the BP-ANN model is superior in regressing and predicting than the Arrhenius-type constitutive equation.

Hot deformation behavior and microstructure evolution of non-equimolar Ti2ZrHfV0.5Ta0.2 refractory high-entropy alloy

This work aims to elucidate the hot deformation behavior and microstructure evolution of a non-equimolar TiZrHf-rich refractory high-entropy alloy (RHEA) with a composition of Ti2ZrHfV0.5Ta0.2 (at. %). The as-cast Ti2ZrHfV0.5Ta0.2 alloy composed solely of a body-centered cubic phase showed superior tensile mechanical properties with a yield strength of 865 MPa and a total elongation of 22.5%. The uniaxial compression tests were performed at temperatures ranging from 900 to 1100 °C and strain rates varying from 10−3 to 10−1 s−1. The relation among the flow stress, deformation temperature, and strain rate was represented by the Arrhenius-type constitutive equations. The calculations show a comparatively low apparent activation energy of 144–119 kJ/mol over the entire range of strains, revealing a noticeable contradiction between the concentration of group IV elements (Ti, Zr, Hf) and the high-temperature strength. The excessive addition of Group IV elements tends to deteriorate the high-temperature strength due to the relatively low melting points and self-diffusion activation energies of Group IV elements. The misorientation analysis based on electron back-scattered diffraction indicated that the dynamic recrystallization mechanism depends strongly on the thermo-mechanical processing conditions. A low deformation temperature and high strain rate results in an abnormal discontinuous dynamic recrystallization mechanism. Additionally, the dominant role played by the edge dislocation in RHEAs during deformation is supposed to be the reason for the abnormal discontinuous dynamic recrystallization mechanism. A series of stress drops were observed under low deformation temperatures and high strain rates. Based on an interrupted hot-compression experiment and a strain aging experiment, the stress drop can be attributed to the unlocking of dislocations pinned by the Cottrell atmosphere or short-range ordering.

Hot deformation behavior of Sc/Nb modified AA2195 Al–Li–Cu alloys

The hot workability of third generation AA2195 (Al–Li–Cu–Ag–Mg–Zr) alloy with different Sc (0.15–0.25 wt%) and Nb (0.15–0.25 wt%) additions in the homogenized condition was investigated using processing maps approach. The additions of Sc and Nb were found to be beneficial in refining the as-cast grain size of AA2195 and changing the morphology from less dendritic grain structure to a globular or equiaxed form. Hot compression tests carried out in the temperature, T, range of 300–450 °C and strain rate, ε˙, of 10−3 – 10 s−1 were utilized to generate processing maps at a true strain, ε = 0.5. The flow curves of the alloys exhibit a typical dynamic recovery (DRV) characteristics and Arrhenius type constitutive equations successfully predicted flow stress of the alloys. The results obtained from the processing maps and complementary microstructural analysis of the deformed specimens revealed that 0.15 wt% additions of Sc and Nb (separately or in combination) are optimum to improve its workability. However, increasing Sc and Nb contents to 0.25 wt% relatively expanded flow instability regions. With the aid of the processing maps, deformed specimens microstructural analysis, activation energy and Zener-Hollomon parameter, Domain D-3 occurring at higher temperatures and strain rates were identified as the “safe” regimes for hot working of AA2195 with optimum Sc and Nb contents (0.15 wt% added separately or in combination). Limited pancake type grain morphology with higher fractions of dynamically recrystallized (DRX) grains was observed in Domain D-3. The microstructural manifestation in the flow instability regions was flow localization (at higher strain rates), cavities formation at the grain boundaries & precipitates, particles breakage and wedge cracking at the triple junctions at lower strain rates.

Constitutive modeling of hot deformation behavior of AlCrFeNi multi-component alloy

In present paper, the hot deformation behavior of an equiatomic AlCrFeNi medium entropy alloy (MEAs) was investigated. 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 flow stress analysis was performed on AlCrFeNi MEAs by using Arrhenius type relationship, and a linear dependence of flow stress on Zener–Hollomon parameter (Z) can be determined. Moreover, a comparative study was carried out to further evaluate the predictability of the Arrhenius-type constitutive equation and artificial neural network (ANN), support vector machine (SVM) model. The results show that the constitutive model developed by SVM performs better to describe the interdependency between deformation temperature, strain rate and flow stress. The activation energy (Q) for high-temperature deformation was calculated as 376.6 kJ/mol, and the related strain rate sensitivity (m), the power dissipation (η), and instability parameter (ξ) were also derived. The processing maps suggest that the flow instability tends to occur at high strain rate and the optimum processing parameters can be determined to direct the hot working process.