Deformation Activation Energy Research Articles

Superplastic deformation mechanical behavior and constitutive modelling of a near-α titanium alloy TNW700 sheet

TNW700 is a newly developed near-α high temperature titanium alloy and has great application potential in the aerospace industry owing to excellent creep strength and short-term service temperature up to 700 °C. The superplastic tensile deformation behavior and constitutive model of TNW700 alloy in the temperature range of 900–975 °C and strain rate range of 0.0005–0.01s−1 were investigated. Results indicated that TNW700 alloy exhibits significant work hardening behavior, which may be related to dynamic growth of β grains, dislocation evolution, and silicide precipitates. In addition, work hardening coefficient (n) as well as the critical strain between flow hardening and softening increases with decreasing strain rate, and first increases and then decreases with increasing deformation temperature. TNW700 alloy exhibits excellent superplasticity at 900 °C–950 °C corresponding to strain rate sensitivity exponent (m) greater than 0.3, and expresses poor superplasticity at 975 °C with lower m value. The m value decreases monotonously with strain owing to decrease of grain boundary sliding contribution caused by dynamic grain growth of β grains. The deformation activation energy increases with decreasing strain rate due to the change of deformation mechanism. A phenomenological constitutive model considering strain hardening, strain rate hardening and temperature softening was proposed and material constants were calibrated by true stress-strain data. The constitutive model was implemented into Abaqus code by UHARD subroutine to simulate the superplastic forming of cone parts, and thickness distribution and bulging heights under different forming time were used to verify the validity of constitutive model.

Deformation behavior during hot processing of the alloy of the Al-Mg system economically doped with scandium

Hot deformation behavior of the new alloy 1580 sparingly doped with scandium (Al-5Mg-0.6Mn-0.10Sc-0.11Zr) was studied under the deformation temperature ranging from 350 to 450 °C and strain rate ranging from 0.01 to 10 s−1. Hot deformation by uniaxial compression and torsion was carried out on a Gleeble 3800 thermomechanical simulator. Hot deformation of the alloy 1580 is accompanied by dynamic softening with the establishment of a balance between the rates of nucleation and annihilation of dislocations. Alloy flow stresses increase with increasing strain rate and decreasing temperature. The experimental results for the new alloy are in full agreement with the known concepts that the combined effect of temperature and strain rate on the deformation behavior of metallic materials is described by the Zener-Hollomon parameter. The deformation activation energy of the alloy obtained by the regression analysis of steady-state flow stresses is 175.7 kJ/mol. When using the steady-state flow stresses normalized to the shear modulus, the deformation activation energy is 148.8 kJ/mol and is close to the activation energy of self-diffusion of aluminum. Analytical expressions are obtained for steady-state flow stresses as a function of the Zener-Hollomon parameter, which make it possible to predict the deformation resistance of the alloy 1580 in a wide range of temperatures and strain rates. This result is important for FEM modeling and for the choice of temperature and stain rate of hot deformation of the alloy under study. Comparison with the literature data showed that in the region of high temperatures and low strain rates, the flow stresses are weakly dependent on the scandium content in the alloy. However, with a decrease in the temperature and an increase in the strain rate, an increase in the scandium content in the alloys leads to a noticeable increase in the flow stresses. In torsion tests, a sharp increase in the ductility of the alloy is observed at a temperature of about 400 °C. One of its probable causes may be dissolution of particles Al3(Sc,Zr) during hot deformation in this high-temperature region.

Effects of C and N on high-temperature deformation behavior of 15Cr–15Mn–4Ni austenitic stainless steels

The effect of interstitial C and N atoms on high-temperature deformation behavior was investigated in 15Cr–15Mn–4Ni austenitic stainless steels containing 0.1–0.3 wt% of either C or N. Single-hit compression tests were performed in the deformation temperature range 800–1100 °C and the strain rate range 0.01–1 s−1. In both C-added (+C) and N-added (+N) steels, the high-temperature strength, i.e. mean flow stress, increased as the concentration of C or N increased. At the same level of C or N concentration, the mean flow stress, activation energy for high-temperature deformation, and degree of lattice expansion were larger in +N-steels than in +C-steels, whereas the dynamically recrystallized grain size and grain growth rate were larger and faster in +C-steels than in +N-steels. The higher strength of +N-steels over + C-steels at a wide range of temperatures was attributed to the stronger solid solution hardening effect of N atoms compared to C atoms. Dynamic recrystallization was relatively retarded in the +N-steels, because N atoms interacted strongly with grain boundaries.

The constitutive modeling and processing map of homogenized Al-Mg-Si-Cu-Zn alloy

The true stress-strain curve of Al-Mg-Si-Cu-Zn alloy under the condition of temperature from 350 °C to 500 °C and strain rate from 0.01 s−1 to 10 s−1 was obtained by Gleeble-3500 thermal-mechanical simulator. Based on these data, the constitutive equation of aluminum alloy is established by using hyperbolic sinusoidal model, and the average hot deformation activation energy Q = 256 kJ/mol is obtained. The model established can well predict the flow behavior of Al-0.9Mg-0.7Si-0.3Cu-0.6Zn alloy, and the average absolute relative error (AARE) between the predicted value and the experimental value is 6.3 %. The processing map was developed according to dynamic material science model (DMM) and Prasad’s criterion and the optimum hot working window is found to be 470 °C -500 °C/0.1 s−1-0.01 s−1. The microstructure evolution of aluminum alloy during isothermal compression deformation was analyzed by transmission electron microscopy (TEM). It was found that DRV is the main dynamic softening mechanism under experimental deformation conditions.

Dynamic Softening Mechanisms and Microstructure Evolution of TB18 Titanium Alloy during Uniaxial Hot Deformation

In this study, isothermal compression tests of TB18 titanium alloy were conducted using a Gleeble 3800 thermomechanical simulator for temperatures ranging from 650 to 880 °C and strain rates ranging from 0.001 to 10 s−1, with a constant height reduction of 60%, to investigate the dynamic softening mechanisms and hot workability of TB18 alloy. The results showed that the flow stress significantly decreased with an increasing deformation temperature and decreasing strain rate, which was affected by the competition between work hardening and dynamic softening. The hyperbolic sine Arrhenius-type constitutive equation was established, and the deformation activation energy was calculated to be 303.91 kJ·mol−1 in the (α + β) phase zone and 212.813 kJ·mol−1 in the β phase zone. The processing map constructed at a true strain of 0.9 exhibited stability and instability regions under the tested deformation conditions. The microstructure characteristics demonstrated that in the stability region, the dominant restoration and flow-softening mechanisms were the dynamic recovery of β phase and dynamic globularization of α grains below transus temperature, as well as the dynamic recovery and continuous dynamic recrystallization of β grains above transus temperature. In the instability region, the dynamic softening mechanism was flow localization in the form of a shear band and a deformation band caused by adiabatic heating.

Hot deformation behavior and 3D processing map of super austenitic stainless steel containing 7Mo–0.46N–0.02Ce: Effect of the solidification direction orientation of columnar crystal to loading direction

In the present paper, hot compression tests on a super austenitic stainless steel (SASS) containing 7Mo–0.46N–0.02Ce were performed at temperatures of 900 °C-1200 °C and strain rates of 0.01–10 s−1. The effect of angle between solidification direction of columnar crystal and loading direction (0°, 30°, 60°, and 90°) on the flow behavior and microstructure evolution of SASS was studied. Results showed that, samples with different columnar crystal characteristics and test conditions displayed various flow behaviors due to the difference in dynamic restoration softening mechanism, flow localization, and shear band formation. With the decrease of the angle between the solidification direction of columnar crystal and loading direction, the deformation activation energy (Q) and the ln Z value of SASS decreased at the true strain of 0.7. It indicates that dynamic recovery (DRV) and dynamic recrystallization (DRX) are more likely to happen in the samples with low angles. The location and range of high efficiency of power dissipation (η) region and instability region of the samples differed much with different columnar crystal characteristics. This means obviously different hot workability and microstructure evolution behaviors. At the true strain of 0.7, no negative η-value region was observed in the 0° sample, and the range of instability region was relatively small. On the whole, SASS presented the optimum hot workability when the angle between the solidification direction of columnar crystal and loading direction was 0°.

Hot Deformation Behavior and Processing Maps of a New Ti-6Al-2Nb-2Zr-0.4B Titanium Alloy.

The hot deformation behaviors of a new Ti-6Al-2Nb-2Zr-0.4B titanium alloy in the strain rate range 0.01–10.0 s−1 and temperature range 850–1060 °C were evaluated using hot compressing testing on a Gleeble-3800 simulator at 60% of deformation degree. The flow stress characteristics of the alloy were analyzed according to the true stress–strain curve. The constitutive equation was established to describe the change of deformation temperature and flow stress with strain rate. The thermal deformation activation energy Q was equal to 551.7 kJ/mol. The constitutive equation was On the basis of the dynamic material model and the instability criterion, the processing maps were established at the strain of 0.5. The experimental results revealed that in the (α + β) region deformation, the power dissipation rate reached 53% in the range of 0.01–0.05 s−1 and temperature range of 920–980 °C, and the deformation mechanism was dynamic recovery. In the β region deformation, the power dissipation rate reached 48% in the range of 0.01–0.1 s−1 and temperature range of 1010–1040 °C, and the deformation mechanism involved dynamic recovery and dynamic recrystallization.

Effect of initial microstructure on hot deformation behavior of AlMg5Si2Mn alloy

In this study, the hot deformation behavior of high-temperature annealed and as-cast AlMg5Si2Mn aluminum alloy was investigated in compression tests carried out between 350 and 430 °C, with a strain rate of 0.005–0.5 s−1, using a DIL 805A/D quenching-deformation dilatometer equipped with an accessory that allowed hot compression tests to be performed in either a vacuum or an inert gas atmosphere. To reveal the mechanism of hot deformation, the flow stress behavior and microstructural evolution were investigated after the hot compression tests. Constitutive constants for the as-cast and annealed state were then calculated and compared. The results show that the alloy in the annealed state exhibited lower deformation resistance under the same deformation conditions, especially at low deformation temperatures. The activation energies for deformation, Q, for the as-cast and annealed conditions were calculated to be 181 kJ*mol−1 and 169 kJ*mol−1, respectively.

Microstructure and Hot Deformation Behavior of the Mg-8 wt.% Sn-1.5 wt.% Al Alloy.

Mg–Sn–Al alloy is a new type of heat-resistant magnesium alloy with great potential and the hot deformation process of this alloy is of great significance for its application. The microstructure, hot deformation behavior, textural evolution, and processing map of a Mg–8 wt.% Sn–1.5 wt.% Al alloy were studied. A Gleeble 1500 D thermo-mechanical simulator was used. The temperature of deformation was 653 to 773 K, the strain rate was 0.001–1 s−1, and the maximum deformation degree was 60%. The obtained results show that the rheological stress of the alloy decreases with an increase in deformation temperature and increases with an increase in the strain rate. The alloy is completely dynamically recrystallized at 653 K, and the entire structure is formed of homogeneous crystals/grains, with small secondary phase particles distributed at the crystal boundary. The mean apparent activation energy of hot compression deformation is 153.5 kJ/mol. The Mg–8 wt.% Sn–1.5 wt.% Al alloy exhibits excellent plastic deformation properties, an expansive thermal processing interval, and a narrow instability zone under the test temperature and deformation rate. The optimal process parameters of the alloy comprise deformation temperatures between 603 and 633 K and strain rates of 0.03 to 0.005 s−1.

Effect of temperature and strain rate on the deformation behavior of Ti5321 during hot-compression

The effect of deformation temperature and strain rate (collectively described by the Zener-Hollomon parameter Z) on the deformation mechanism and texture formation of the metastable β-titanium alloy Ti5321 across the β-transus temperature during hot-compression was investigated by electron backscatter diffraction. In the β-phase field, it is found that the deformation behavior and texture formation varies depending on Z. With decreasing Z dynamic recovery and dynamic recrystallization become more and more important. The activation energy for steady state deformation is 240 kJ/mol and 370 kJ/mol in the β- and (α + β)-phase field, respectively. The texture developed is a<100> <111> double-fiber with<100>dominating at all deformation conditions. The<111> fiber gets more prominent with increasing Z suggesting that it is mainly related to deformation. Flow softening behavior of Ti5321 is associated with dynamic globularization of the α-phase and promotion of β-grain formation by continuous dynamic recrystallization.

High temperature nanoindentation as a tool to investigate plasticity upon phase transformations demonstrated on Cobalt

A new field of application for high temperature nanoindentation as a complimentary method to understand the mechanics of plasticity upon bulk phase transformations in thermodynamic equilibrium is introduced. The feasibility is outlined on polycrystalline Cobalt involving a low-temperature hexagonal closed packed phase, and above 700K, a high-temperature face centered cubic phase, which was conventionally characterized by means of differential scanning calorimetry and high temperature X-ray diffraction. Strain rate sensitivity, activation volume and activation energy of plastic deformation were determined up to 873 K to identify the rate-controlling deformation mechanism. From RT to 473 K plasticity was found to be controlled by lattice friction on the basal plane, where dislocations have to overcome the Peierls barrier and deformation twinning was apparent in the hexagonal phase. The thermal activation of cross slip lead to reduced twinning actions when the phase transition temperature is approached. In the high temperature face centered cubic phase deformation was found to be controlled by cutting of forest dislocations and no deformation twinning was observed.

The Significant Impact of Ti Addition on the Hot Deformation Behavior of Medium‐Manganese Microalloyed Steel

The constitutive analysis and microstructural characteristics of Ti microalloyed medium‐Mn steel are studied here by hot deformation test in the temperature range of 1123–1473 K and at the strain rates from 0.01 to 10 s−1 based on thermal simulation. Furthermore, the effect of Ti addition on hot deformation behavior is elucidated. The results indicate that the fluctuation of flow stress, which is sensitive to deformation conditions, is a result of dynamic equilibrium between strain hardening and thermally activated work softening. Flow stress constitutive equations for low Ti and high Ti content steels are developed with an average deformation activation energy Q of 456.1 and 350.9 kJ mol−1, respectively. The morphologies of prior austenite grain (PAG) and dynamic recrystallization (DRX) behavior are dramatically influenced by the compression parameters and the Ti content. The PAG size decreases with the increase in the Ti content, which can accelerate the progress in the DRX process. As a result, the refined martensite lath is obtained in the steel with high Ti content.

Hot deformation activation energy of a 5E83 alloy prepared with centrifugal casting

5E83 aluminum pipe was produced withy centrifugal casting, the hot deformation were performed on the inner, middle, and outer layers of the pipe, the hot deformation activation energy Q were calculated. The results revealed that the hot deformation flow stresses exhibited increase tendency along with the inner, middle, and outer layer, the hot deformation activation energy Q increased from 164.5MPa for the inner layer to 197.6 and 214.9MPa for the middle and the outer layer respectively. Along with the layer of inner, middle, and outer, the solid solution level increased and the grain size decreased. Correspondingly, the solid solution hardening became stronger and the grain refinement mechanism was enhanced, resulting in the increased hot deformation flow stresses and activation energy Q.

Flow Stress Behavior and Microstructural Evolution of DC Cast 7065 Aluminum Alloy During Hot Compression Deformation

The deformation behavior and microstructure evolution of DC cast 7065 aluminum alloy was investigated in the temperature range of 340-460 ℃ and strain rate range of 0.1-8 s-1. The flow stresses of the 7065 alloy are forceful function of deformation strain rate and temperature. The peak stress raises with reducing compression temperature, and at a designated deformation temperature, the peak stress increases with the increasing of strain rate. The hot deformation equation of the alloy is generated, and the deformation activation energy of the alloy is 117.869 kJ/mol. When the samples were deformed above 380℃, the α-aluminum dendrite in the initial microstructure was replaced by recrystallized grains, dynamic recrystallisation occurred during compression.

Hot Deformation Behaviors in Ti-6Al-4V/(TiB + TiC) Composites

Thermal compression testing was investigated using the Gleeble 3800 thermal simulator, and thermal deformation behavior of particle-reinforced titanium matrix composites (TMCs) was studied under deformation temperatures of 750–900 °C, strain rates of 0.001–1 s−1, and experimental deformation of 60%. According to obtained flow stress curves, the hot deformation characteristics were analyzed. Based on the Arrhenius hyperbolic sinusoidal model, the constitutive equation at high temperature was established. Based on the theory of dynamic material models, a hot processing map of TMCs at high temperature was established, and the peak region of power dissipation rate and the instability region in the hot processing map were both determined. At the same time, the corresponding microstructures in the peak power dissipation rate and rheological instability regions were observed. The results showed that flow stress decreased with increasing deformation temperature and increased with increasing strain rate. The thermal deformation activation energy of titanium matrix composites was 301.8 kJ/mol. The Ti-6Al-4V/(TiB + TiC) composites possessed only one instability zone under high-temperature compression at a strain of 0.5, with corresponding temperatures at 750–840 °C and strain rates at 0.1–1 s−1. The optimal thermal deformation parameters included corresponding temperatures of 830–880 °C and strain rates of 0.001–0.05 s−1. The microstructures corresponding to optimal hot working parameters in processing maps were more homogeneous than the microstructures in the instability zone, including the distribution uniformity of reinforcement and the degree of dynamic recrystallization, and no instability phenomena including abnormal grain growth, microcracks or intensive fracture of reinforcements were found, indicating that the hot processing map had a positive guiding effect on the option of desirable material thermal-working parameters.

High-Temperature Deformation Characteristics and Constitutive Model of an Ultrahigh Strength Steel

The high-temperature deformation characteristics of an ultrahigh strength steel is studied by hot compression tests under the deformation temperatures of 920–1160 °C and strain rates of 0.01–10 s−1. By employing the metalloscope and transmission electron microscope, the influences of deformation parameters (deformation temperature and strain rate) upon microstructure evolution are analyzed in detail. Results show that the hot deformation activation energy of the studied steel is estimated as 332.3 kJ/mol. The microstructure presents the typical dynamic recrystallization (DRX) features, and the DRX behaviors are mainly dominated by the discontinuous DRX mechanism under different deformation parameters. Under the low strain rate or the high deformation temperature, the continuous DRX behavior caused by the rotation of subgrains takes place. For forecasting the deformation stress of the studied steel, a physically-based constitutive model is constructed by combining dislocation density theory and DRX kinetics. The reproduced deformation stresses well close to the measured data indicates that the developed physically-based constitutive model enjoys a preferred prediction ability to forecast the high-temperature deformation behaviors for the studied steel.

Establishment of flow stress model and optimization of process parameters for ZK10 magnesium alloy with low zinc-content during isothermal compression

Under the condition of strain rates of 0.001–1 s−1 and temperatures of 473–723 K, the flow behaviors of the cast-homogenized ZK10 magnesium alloy were studied through the isothermal compression test with final true strain of 1. In view of this, the Arrhenius equation subject to strain was treated with a comprehensive correction, the deformation activation energy Q of ZK10 alloy was calculated to be 181.87 kJ/mol, and a reliable flow stress model of ZK10 alloy was established. Meanwhile, the processing maps and microstructure evolution of ZK10 alloy were analyzed, which indicated that obvious dynamic recrystallization occurred during thermal compression deformation of ZK10 alloy under the above process conditions. When ZK10 alloy was hot compressed at 473 K in the instability zone, serious instability deformation and macro cracks occurred at strain rates of 0.001 s−1 and 0.01 s−1. The optimum process parameter of ZK10 alloy under the experimental conditions was obtained to be 673 K/1 s−1, and the corresponding microstructure was the most uniform and finest, which provides useful guidance for the selection of process parameters of ZK10 alloy.

A Comparative Study on the Activation Energy for Hot Deformation of 5CrNiMoV and S34MnV Steel

Background: The value of the activation energy is dependent on deformation conditions and sensitive to the difference in the alloying element. The research on the evolution of the activation energy with strain and alloying elements plays an important role in analyzing the mechanism of hot deformation. Objective: The purpose was to clarify the activation energy evolution with strain, to analyze strengthening or softening mechanism of each element and acquire an empirical equation for medium carbon steels to quantitatively describe the effect of each element on activation energy. Methods: Hot compression tests of the two medium carbon steel were conducted. The value of activation energy at different strain was obtained by fitting the experiment results. Through the analysis of medium carbon steels with different composition in published papers, the empirical relationship between thermal activation energy and chemical composition can be fitted. Results: It was found that the activation energy showed significant dependence on the strain and chemical composition. The activation energy’s evolution with strain was revealed. An empirical expression for medium carbon steels was proposed to characterize the influence of the chemical composition on the activation energy. It was found that the microalloying elements Nb, Ti, V and Mo, as the main solution strengthener and precipitation strengthener, have a positive effect on the activation energy. Conclusion: The evolution of the activation energy with strain was revealed and the corresponding hot deformation mechanism was analyzed through the activation energy. An empirical expression was acquied to characterize the influence of the chemical composition on the activation energy for medium carbon steels, which would be used for the research on new materials.

Effects of vanadium concentration on mechanical properties of V NbMoTa refractory high-entropy alloys

Abstract Mechanical properties and strengthening, deformation, and/or fracture mechanisms of refractory high-entropy alloys VxNbMoTa are investigated. At room temperature, both the yield strength and ductility of VxNbMoTa are greatly improved when increasing the V concentration, which can be related to the enhanced solid solution strengthening and the grain refinement. The fracture morphologies of VxNbMoTa experience the intergranular-to-transgranular transition as increasing the V content. The better ductility of high vanadium alloys should attribute to the refined grains and reduced impurities and brittle compounds at the grain boundary as revealed by atom probe tomography. At 800 °C and 1000 °C, the VxNbMoTa alloys of higher V concentrations exhibit weaker strain hardening rates, while this is opposite at room temperature. This can be explained by the decreased activation energy of hot deformation as increasing the V concentration at elevated temperatures, as indicated by flow stress analyses using the strain-compensated Arrhenius-type model with improved predictability.

Effect of a High Mg Solute Content on the Hot Workability of Al-Mg Alloys.

The workability of Al-xMg alloys with a high Mg content (Al-6Mg, Al-8Mg, Al-9Mg) was evaluated by investigating the microstructure and processing map. Hot torsion tests were conducted in the range of 350-500 °C between 0.1 and 1 s-1. Constitutive equations were derived from various effective stress-strain curves, and the thermal activation energies for deformation obtained were 171 kJ/mol at Al-6Mg, 195 kJ/mol at Al-8Mg, and 220 kJ/mol at Al-9Mg. In the case of the processing map, the instability region, which widened with increasing Mg content, was due mainly to the influence of the Mg solute, which activated grain boundary cracking and flow localization.