Modeling Of Hot Deformation Behavior Research Articles

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.

New constitutive equation utilizing grain size for modeling of hot deformation behavior of AA1070 aluminum

A new phenomenological and empirically-based constitutive model was proposed to modify the term in the original Johnson–Cook constitutive model. The new model can be used to describe and predict the flow stress of AA1070 aluminum with different initial grain sizes in the hot working process. This developed model considers thermal softening, strain-rate hardening, strain hardening, initial grain size, and interactions with each other and can correctly model the behavior of AA1070 at elevated temperature with different strains, strain rates, and initial grain sizes. The hot flow behavior of AA1070 was investigated through compression tests over wide ranges of temperature from 623 to 773 K, strain rate from 0.005 to 0.5 s −1 and initial grain size from 50 to 450 μm. Results show that the initial grain size has a significant effect on the flow behavior of AA1070. Then, correlation coefficient ( R ), average absolute relative error (AARE), and relative error were examined for comparative predictability of the model. Results show that flow stresses for different initial grain sizes calculated by the new proposed model perfectly correlate with experimental ones, with a mean relative error of 1.19%, which confirms that the new modified Johnson–Cook relation can give a precise estimation of the hot flow stress of AA1070 aluminum by considering the initial grain size.

Characterization and Modeling of Hot Deformation Behavior of a Copper-Bearing High-Strength Low-Carbon Steel Microalloyed with Nb

This study investigates hot deformation behavior of a newly developed Cu-bearing high-strength low-carbon steel microalloyed with Nb (Nb-HSLC). A computational method based on experimental data was employed to design the chemical composition of the alloy. Compression tests were carried out in the temperature range of 850-1100 °C as well as strain rates of 0.001-10 s−1 using BAHR Dil 805 A/D thermo-analyzer equipment. The Arrhenius-type constitutive equations were used to model the hot working behavior of the designed steel. Effects of friction and temperature rise during deformation were corrected to obtain the actual stresses. The results showed that the peak flow stress was increased with increasing Zener–Hollomon parameter. The obtained flow curves at strain rates lower than 0.1 s−1 and temperatures above 950 °C represented the typical dynamic recrystallization (DRX) behavior, while the flow curves at temperatures lower than 950 °C at all strain rates were associated with continuous strain hardening. This feature is in good agreement with the precipitation temperature range of Nb(C, N) particles, i.e., 800-1000 °C. Moreover, the flow curves showed the serrations during hot deformation at strain rates of 0.001 and 0.01 s−1, indicating that the dynamic strain aging (DSA) phenomenon occurred at low strain rates. The best fit between “peak stress” and “deformation conditions” was obtained by a hyperbolic sine-type equation (R2 = 0.993). Therefore, the average activation energy was determined as 348 kJ mol−1. The agreement between the achieved model and experimental flow data was verified using the results of additional tests at a strain rate of 5 s−1. The maximum difference between the measured and predicted “peak stresses” was calculated as 5 Mpa.

Modeling of hot deformation behavior of high phosphorus steel using Johnson-Cook model

To describe the hot deformation behavior of high phosphorus steel, isothermal hot compression test was performed using Gleeble 3800 thermo-mechanical simulator in the temperatures ranging from 750-1050°C at constant strain rates of 0.001-10 s−1. Based on the experimental results, Johnson-Cook model was developed to predict the values of flow stress. Johnson-Cook model shows a fairly good agreement with experimental and predicted values. Average absolute relative error (AARE), and relative error (RE) of JC model are calculated as 24.356%, and - 19.97% to 33.179%, respectively.

Modeling of hot deformation behavior and prediction of flow stress in a magnesium alloy using constitutive equation and artificial neural network (ANN) model

Abstract The aim of the present study was to investigate the modeling and prediction of the high temperature flow characteristics of a cast magnesium (Mg–Al–Ca) alloy by both constitutive equation and ANN model. Toward this end, hot compression experiments were performed in 250–450 °C and in strain rates of 0.001–1 s−1. The true stress of alloy was first and foremost described by the hyperbolic sine function in an Arrhenius-type of constitutive equation taking the effects of strain, strain rate and temperature into account. Predictions indicated that unlike low strain rates and high temperature with dominant DRX activation, in relatively high strain rate and low temperature values, the precision of the models become decreased due to activation of twinning phenomenon. At that moment and for a better evaluation of twinning effect during deformation, a feed-forward back propagation ANN was developed to study the flow behavior of the investigated alloy. Then, the performance of the two suggested models has been assessed using a statistical criterion. The comparative assessment of the gained results specifies that the well-trained ANN is much more precise and accurate than the constitutive equations in predicting the hot flow behavior.

Constitutive Modeling of Hot Deformation Behavior of High-Strength Armor Steel

The hot isothermal compression tests of high-strength armor steel under a wide range of deformation temperatures (1100-1250 °C) and strain rates of (0.001-1/s) were performed. Based on the experimental data, constitutive models were established using the original Johnson-Cook (JC) model, modified JC model, and strain-compensated Arrhenius model, respectively. The modified JC model considers the coupled effects of strain hardening, strain rate hardening, and thermal softening. Moreover, the prediction accuracy of these developed models was determined by estimating the correlation coefficient (R) and average absolute relative error (AARE). The results demonstrate that the flow behavior of high-strength armor steel is considerably influenced by the strain rate and temperature. The original JC model is inadequate to provide good description on the flow stress at evaluated temperatures. The modified JC model and strain-compensated Arrhenius model significantly enhance the predictability. It is also observed from the microstructure study that at low strain rates (0.001-0.01/s) and high temperatures (1200-1250 °C), a typical dynamic recrystallization (DRX) occurs.

Modeling of hot deformation behavior with dynamic recrystallization in TC4 titanium alloy

Abstract Isothermal compression tests of TC4 titanium alloy over a temperature range of 973 K to 1123 K and strain rate range of 0.1 s−1 to 30 s−1 showed that dynamic recrystallization (DRX) occurred under all deformation conditions. To model the flow stress taking into account the DRX behavior, the model was divided into two stages by the critical strain of DRX (∊c) calculated using the Poliak–Jonas method. The flow stress in the first stage with no DRX (∊ ≤ ∊c) was described by the Estrin–Mecking equation. The flow stress in the second stage with DRX (∊ > ∊c) was expressed by the interaction of work hardening, dynamic recovery, and DRX. The function relationship between the principal parameters in the flow stress model and the deformation conditions described by the Zener–Hollomon parameter was also analyzed. The prediction of the constructed flow stress model agreed well with the experimental results.

Constitutive modeling of hot deformation behavior of vacuum hot pressed Cu–8Cr–4Nb alloy

Abstract In the present study, atomized Cu–8Cr–4Nb alloy powder having in-situ formed Cr 2 Nb precipitates was vacuum hot pressed to near theoretical density. The hot-pressed alloy was hot isothermally compression tested at temperatures of 800 °C, 850 °C, 900 °C and 950 °C and strain rates of 0.01 s −1 , 0.1 s −1 , 1 s −1 and 10 s −1 to study the deformation behavior. The effect of friction between sample and compression die was evaluated and was found to be quite low. The measured flow stress data was used for the development of constitutive model for hot deformation behavior Cu–8Cr–4Nb alloy. The activation energy for hot deformation of hot-pressed Cu–8Cr–4Nb alloy was calculated to be 436.89 kJ/mol, which is significantly higher than that of the pure copper. The higher activation energy is attributed to the presence of Cr 2 Nb precipitates which are expected to generate threshold stress and reduce the effective stress available for thermal deformation.

Constitutive modeling of hot deformation behavior of X20Cr13 martensitic stainless steel with strain effect

Hot deformation behavior of X20Cr13 martensitic stainless steel was investigated by conducting hot compression tests on Gleeble–1500D thermo-mechanical simulator at the temperature ranging from 1173 to 1423 K and the strain rate ranging from 0.001 to 10 s−1. The material constants of α and n, activation energy Q and A were calculated as a function of strain by a fifth-order polynomial fit. Constitutive models incorporating deformation temperature, strain rate and strain were developed to model the hot deformation behavior of X20Cr13 martensitic stainless steel based on the Arrhenius equation. The predictable efficiency of the developed constitutive models of X20Cr13 martensitic stainless steel was analyzed by correlation coefficient and average absolute relative error which are 0.996 and 3.22%, respectively.

Modeling of Hot Deformation Behavior of 55SiMnMo Medium-Carbon Steel

The hot deformation behavior of 55SiMnMo steel was studied by hot isothermal compression tests at 950 — 1 100 °C and strain rates of 0.01 — 10s−1 using a Gleeble 3500 thermal simulation machine. Experimental results show that the peak stress increases with decreasing deformation temperature and increasing strain rate. When the strain rate ▪ = 0.01s−1, or when ▪ = 0.1s−1 and the deformation temperature T ≥ 1000 °C, the dynamic recrystallization (DRX) of 55SiMnMo steel occurs. The hot flow stress constitutive equation, peak strain equation, as well as critical stress and strain for DRX initiation are obtained based on the experimental data. A comparison between the theoretical and experimental results verifies the reliability of the flow stress equation.

Constitutive Modeling of Hot Deformation Behavior of the AA6063 Alloy with Different Precipitates

The current study proposes a simple constitutive model that integrates the kinetics of precipitation during static aging and the kinetics of precipitate dissolution during preheating to deformation temperature to predict the hot flow behavior of AA6063 alloy. The model relates the flow behavior of the age-hardenable alloy to the alloy chemistry, thermal history as well as deformation temperature, strain, and strain rate by means of a physically based model. Different aging conditions, including supersaturated solid solution and overaging conditions with different deformation parameters, were assessed. Each part of the model was in good agreement with those of experimental and other model results published in the literature.

Constitutive modeling of hot deformation behavior of H62 brass

Abstract The hot deformation behaviors of H62 brass are investigated by isothermal compression tests on a Gleeble 1500 thermal-mechanics simulator in the temperature range of 650–800 °C and the strain rate range of 0.01–10 s −1 . Most of the stress–strain curves exhibit a single peak stress, indicating a typical dynamic recrystallization (DRX) behavior of the alloy. Further microstructural observation confirms the occurrence of DRX behavior and the β → α phase transformation of H62 brass under the deformation conditions. A new constitutive equation coupling flow stress with strain, strain rate and deformation temperature is developed on the basis of the Arrhenius-type equation, in which the Zener–Hollomon parameter is modified by considering the compensation of the strain rate. In the constitutive equation, the material constants α , n , Q and A are found to be functions of the strain. The flow stress predicted by the constitutive equation shows good agreement with the experimental stress, which validates the efficiency of the constitutive equation in describing the deformation behavior of the material.