Hot Deformation Activation Energy Research Articles

Hot deformation behavior of Ti–22Al–25Nb alloy by processing maps and kinetic analysis

Abstract

Physically-based constitutive modeling of NiTi intermetallic compound during hot deformation

The hot compression behaviour of a binary nitinol alloy was studied at the temperature range of 700–1000°C under strain rate of 0.1 s− 1. First, the constitutive descriptions of flow stress versus the Zener-Hollomon parameter were used to determine the hot working constants of the investigated material. Subsequently, it was shown that the theoretical exponent of 5 and the self-diffusion activation energy as the hot deformation activation energy can be used in the classical hyperbolic sine equation to describe the peak flow stress, which is in accordance to the deformation mechanism controlled by glide and climb of dislocations. This resulted in a simple and more reliable constitutive equation from the physical and metallurgical standpoints.

Hot Deformation Behavior and Processing Map of Spray Formed M3: 2 High Speed Steel

Hot deformation behavior of a new type of M3 : 2 high speed steel with niobium addition made by spray forming was investigated based on compression tests in the temperature range of 950–1150 °C and strain rate of 0.001–10s−1. A comprehensive constitutive equation was obtained, which could be used to predict the flow stress at different strains. Processing map was developed on the basis of the flow stress data using the principles of dynamic material model. The results showed that the flow curves were in fair agreement with the dynamic recrystallization model. The flow stresses, which were calculated by the comprehensive constitutive equation, agreed well with the test data at low strain rates (≤1 s−1). The material constant (α), stress exponent (n) and the hot deformation activation energy (QHW) of the new steel were 0. 00615 MPa−1, 4.81 and 546 kJ ·mol−1, respectively. Analysis of the processing map with an observation of microstructures revealed that hot working processes of the steel could be carried out safely in the domain (T=1050–1150 °C, ɛ = 0.01–0.1 s−1) with about 33% peak efficiency of power dissipation (η). Cracks was expected in two domains at either lower temperatures (<1000 °C) or low strain rates (0.001 s−1) with different cracking mechanisms. Flow localization occurred when the strain rates exceeded 1 s−1 at all testing temperatures.

Characterization of the hot deformation behavior and microstructural evolution of Ti–6Al–4V sintered preforms using materials modeling techniques

The hot deformation behavior of Ti–6Al–4V sintered preforms was investigated by hot compression tests over temperatures from 800 to 1100 °C and strain rates from 0.001 to 10.0 s−1. The flow curves for the α + β regimes exhibited continuous flow softening and broad oscillation after the peak stress under all of the processing conditions. Otherwise, for the β field, steady-state flow stress was obtained or stress oscillation appeared after the peak stress. In the α + β field, the dynamic globularization and platelet buckling/kinking were observed at lower and higher strain rates, respectively. Unlike in the α + β regions, dynamic recrystallization was found at higher strain rates in the β ones. The apparent activation energies for hot deformation in the α + β and β regimes from kinetic modeling technique were estimated to 147.35 and 233.95 kJ mol−1, respectively. The efficiency of power dissipation over all of the deformation conditions was also calculated by using dynamic material models and schematized into a processing map. The highest value was predicted to 46% at a temperature of 945 °C and at a strain rate of 0.001 s−1, and the processing condition seemed to be optimal for hot deformation of the Ti–6Al–4V sintered preforms.

The physical interpretation of the activation energy for hot deformation of Ni and Ni–30Cu alloys

Abstract

Processing maps for the Cu-Cr-Zr-Y alloy hot deformation behavior

Hot deformation behavior of the Cu-Cr-Zr-Y alloy was studied by hot compressive tests in the 650–850°C temperature and 0.001–10s−1 strain rate ranges using the Gleeble-1500D thermo-mechanical simulator. The flow stress behavior and microstructure evolution were observed during the hot deformation process. The peak stress increases with decreasing temperature and increasing strain rate. The apparent activation energy for hot deformation of the alloy is 336kJ/mol. Based on the dynamic material model, the processing maps for the alloy were obtained at 0.3, 0.4 and 0.5 strain. The evolution of dynamic recrystallization microstructure strongly depends on the deformation temperature and strain rate. Dynamic recovery is the main softening mechanism at low temperature and high strain rate. Dynamic recrystallization appears at high temperatures and low strain rates. The precipitates of chromium-rich particles were observed during hot deformation. The addition of Y can refine the grain and effectively improve the hot workability of the Cu-Cr-Zr alloy. According to the processing maps and microstructure observations, the optimal hot working parameters for the Cu-Cr-Zr-Y alloy are 800–850°C temperature range and 0.01–1s−1 strain rate range.

Flow behavior and microstructure evolution of 6A82 aluminium alloy with high copper content during hot compression deformation at elevated temperatures

The flow behavior and microstructure evolution of 6A82 aluminum alloy (Al–Mg–Si–Cu) with high copper content were studied on a Gleeble–1500 system by isothermal hot compression test in the temperature range from 320 to 530 °C and the strain rate range from 0.001 to 10 s−1. The results reveal that the flow stress of the alloy exhibits a continuous flow softening behavior at low temperatures of 320–390 °C, whereas it reaches steady state at high temperatures (≥460 °C), which are influenced greatly by the Zener–Hollomon parameter (Z) in the hyperbolic sine with the hot deformation activation energy of 325.12 kJ/mol. Microstructure characterizations show that prominent dynamic recrystallization and coarsening of dynamic precipitation may be responsible for the continuous flow softening behavior. Due to deformation heating at high strain rates (≥1 s−1), dynamic recrystallization is more prominent in the specimen deformed at 530 °C and 10 s−1 than in the specimen deformed at 460 °C and 0.1 s−1 even though they have very close ln Z values.

The Hot Deformation Activation Energy of 7050 Aluminum Alloy under Three Different Deformation Modes

In this study, the hot deformation activation energy values of 7050-T7451 aluminum alloy, calculated with two different methods under three deformation modes, were compared. The results showed that the hot deformation activation energy values obtained with the classical constitutive equation are nearly equivalent under the hot tensile, compression, and shear-compression deformation modes. Average values exhibited an obvious increase when calculated with the modified constitutive equation because it can reflect the variation of activation energy with deformation conditions such as deformation temperature, strain rate and strain state. Moreover, the values under tensile and compression deformation modes were nearly the same regardless of the calculation method. The higher average value under the shear-compression deformation mode with modified equation indicates that the strain state has a significant effect on the hot deformation activation energy. In addition, when the activation energy was investigated for various deformation conditions, the effect of the strain state on the activation energy was more significant. Under a certain condition, the activation energy was the same for the three deformation modes.

Hot Deformation Characteristics and Processing Maps of the Cu-Cr-Zr-Ag Alloy

The hot deformation behavior of the Cu-Cr-Zr-Ag alloy has been investigated by hot compressive tests in the 650-950 °C temperature and 0.001-10 s−1 strain rate ranges using Gleeble-1500D thermo-mechanical simulator. The microstructure evolution of the alloy during deformation was characterized using optical and transmission electron microscopy. The flow stress decreases with the deformation temperature and increases with the strain rate. The apparent activation energy for hot deformation of the alloy was 343.23 kJ/mol. The constitutive equation of the alloy based on the hyperbolic-sine equation was established to characterize the flow stress as a function of the strain rate and the deformation temperature. The processing maps were established based on the dynamic material model. The optimal processing parameters for hot deformation of the Cu-Cr-Zr-Ag alloy are 900-950 °C and 0.001-0.1 s−1 strain rate. The evolution of DRX microstructure strongly depends on the deformation temperature and the strain rate.

A Study on Flow Behavior of AA5086 Over a Wide Range of Temperatures

Flow stress behavior of AA5086 was determined using tensile testing at different temperatures from room temperature to 500 °C and strain rates varying between 0.002 and 1 s−1. The strain rate sensitivity parameter and occurrence of dynamic strain aging were then investigated in which an Arrhenius-type model was employed to study the serrated flow. Additionally, hot deformation behavior at temperatures higher than 320 °C was evaluated utilizing hyperbolic-sine constitutive equation. Finally, a feed forward artificial neural network model with back propagation learning algorithm was proposed to predict flow stress for all deformation conditions. The results demonstrated that the strain rate sensitivity at temperature range of 25-270 °C was negative due to occurrence of dynamic strain aging leading to significant reduction in fracture strain. The serrated yielding activation energy was found to be 46.1 kJ/mol. It indicated that the migration of Mg-atoms could be the main reason for this phenomenon. The hot deformation activation energy of AA5086 was also calculated about 202.3 kJ/mol while the dynamic recovery was the main softening process. Moreover, the ANN model having two hidden layers was shown to be an efficient structure for determining flow stress of the examined alloy for all temperatures and strain rates.

Hot Deformation Simulation of Spray Formed 7055 Aluminum Alloy

The hot deformation behavior of spray formed 7055 aluminum alloy was investigated in this paper. Hot compression deformation was performed on Gleeble-3500 thermal-mechanical simulator at strain rate of 0.001-5s-1 and deformation temperature of 573-723K. The result shows that the flow stress of spray formed 7055 aluminum alloy is increased with the increasing of strain rates, while decreased with the increasing of the deforming temperature. The maximum temperature rising induced by deformation heat is 25K during the test at strain rate of 5s-1, and the corrected flow stress is 20MPa higher than measured value. A flow stress constitutive equation is constituted based on Arrhenius hyperbolic sine function containing the Z parameter, and the hot deformation activation energy is 146.91kJ·mol-1. The average absolute relative error (Er) is introduced to evaluate the performance of the developed constitutive equation. The value of Er is 2.89% , which proves the developed constitutive equation can accurately predict the flow stress of the spray formed 7055 aluminum alloy.

Деформационное поведение коррозионностойкой супермартенситной стали в условиях горячей осадки

The deformation behavior of supermartensitic stainless steel 02Cr13Ni4Mo was investigated through compression test using Gleeble-3800 thermo-mechanical simulator within the temperature range of 900–1200 °C and strain rate range of 0,01–10 s –1 . The results showed that the flow stress increases with the drop in the temperature and increasing strain rate. Flow stress of supermartensitic steel exceeds the flow stress of martensitic steel 20Cr13 for same regimes of deformation. Critical strain required to start dynamic recrystallization has similar values for supermartensitic and martensitic steel. The activation energy of hot deformation of supermartensitic steel (442 kJ/mole) is slightly higher than that of martensitic steel (430 kJ/mole). Apparently, this difference is due to a decrease in the carbon content and addition of molybdenum in the supermartensitic steel, which dramatically increases the activation energy of self-diffusion of g-iron.

Compression Deformation Behavior and Processing Map of Pure Copper

To reveal the compression deformation behavior of pure copper, the deformation characteristics of pure copper have been investigated by means of compression tests in the temperature range of 400–900°C and strain rate range of 0.001–1 s–1. The results show that the flow stress of pure copper increases with strain rate and decreasing deformation temperature, which is characterized by work-hardening, dynamic recovery, dynamic recrystallization, secondary work-hardening, etc. The activation energy of hot deformation is associated with deformation temperature and strain rate, and the average activation energy is calculated to be 303.8 kJ/mol. The flow stress prediction model based on GA+BP network provides a very good agreement with the true stress curve, which is instrumental for the guidance of hot working of pure copper. The flow instability occurs in the intermediate strain rate range (0.01–0.1 s–1). Based on the processing map anakysis, the high power dissipation corresponds to the dynamic recrystallization. Appropriate reduction of the deformation temperature or increased strain rate are beneficial for the grain refinement in the steady-state range of the processing map.

Influence of Boron on Initial Austenite Grain Size and Hot Deformation Behavior of Boron Microalloyed Steels

The initial austenite grain size of boron microalloyed steel with three different amounts of boron (20, 40, and 60 ppm) was investigated under different heating temperatures (1150, 1100, and 1050 °C), and hot compression tests of samples in a wide range of temperature (900–1100 °C) and strain rate (0.1–10 s−1) were conducted. It was found that the initial austenite grain size increases with increasing temperature and boron content. The flow stress decreased with increasing boron content at lower strain rates. The flow stress constitutive equation of hot deformation was developed for the experimental steels; results showed that boron addition has the trend to reduce the hot deformation activation energy. The characteristic points of the flow curves were analyzed. Results revealed that the peak and critical stress decreased in response to an increase of boron content. The work-hardening behavior of both steels was investigated, and it was found that boron addition can decrease the work-hardening rate when strained at lower strain rates. On the contrary, peak and critical strains increased as boron content increased, indicating that boron has the ability to delay the onset of dynamic recrystallization.

Evolution of activation energies for hot deformation of 7150 aluminum alloys with various Zr and V additions

The flow stress behavior of 7150 aluminum alloys with different Zr (0–0.15wt%) and V (0.01–0.15wt%) additions was investigated using uniaxial compression tests conducted at various temperatures and strain rates. Using the revised Sellars’ constitutive analysis, the activation energy maps for hot deformation of 7150 alloys are proposed, which are considered as a function of deformation temperature, strain rate and micro-alloying elements. The results reveal that the activation energies of all 7150 alloys decrease with increasing deformation temperature and increasing strain rate. The activation energies for hot deformation of the alloy with 0.12–0.15% Zr are remarkably increased compared with those of the base alloy at most deformation conditions due to the pinning effect of Al3Zr dispersoids on dislocation and the restrained dynamic recovery. The 0.05% V addition significantly increases activation energies, preferentially at lower temperatures of 573–623K, correlated with the V solute drag effect. At higher V additions from 0.11% to 0.15%, the activation energy generally increases at the majority of deformation conditions due to the Al21V2 dispersoid pinning effect. However, remarkable decreases in activation energy are exhibited at low deformation temperatures of 573–700K and at low strain rates of 0.001–0.008s−1, attributed to the enhanced dynamical precipitation and severe depletion of solutes. Comparing the activation energy maps for the alloys studied, the effects of the micro-alloying of Zr and V on plastic deformation under specific deformation conditions can be better understood.

An Investigation into Hot Deformation Characteristics and Processing Maps of High-Strength Armor Steel

The isothermal hot compression tests of high-strength armor steel over wide ranges of strain rates (0.01-10 /s) and deformation temperatures (950-1100 °C) are carried out using Gleeble thermo-simulation machine. The true stress-strain data obtained from the experiments are employed to establish the constitutive equations based on the strain-compensated Arrhenius model. With strain-compensated Arrhenius model, good agreement between the experimental and predicted values is achieved, which represents the highest accuracy in comparison with the other models. The hot deformation activation energy is estimated to be 512 kJ/mol. By employing dynamic material model, the processing maps of high-strength armor steel at various strains are established. A maximum efficiency of about 45% of power dissipation is obtained at high temperature and low strain rate. Due to the high power dissipation efficiency and excellent processing ability in dynamic recrystallization zone for metal material, the optimum processing conditions are selected such that the temperature range is between 1050 and 1100°C and the strain rate range is between 0.01 and 0.1/s. Transmission electron microscopy observations show that the dislocation density is directly associated with the value of processing efficiency.

Hot deformation mechanism and microstructure evolution of an ultra-high nitrogen austenitic steel containing Nb and V

The flow curves of an ultra-high nitrogen austenitic steel containing niobium (Nb) and vanadium (V) were obtained by hot compression deformation at temperatures ranging from 1000°C to 1200°C and strain rates ranging from 0.001 s−1 to 10 s−1. The mechanical behavior during hot deformation was discussed on the basis of flow curves and hot processing maps. The microstructures were analyzed via scanning electron microscopy and electron backscatter diffraction. The relationship between deformation conditions and grain size after dynamic recrystallization was obtained. The results show that the flow stress and peak strain both increase with decreasing temperature and increasing strain rate. The hot deformation activation energy is approximately 631 kJ/mol, and a hot deformation equation is proposed. (Nb,V)N precipitates with either round, square, or irregular shapes are observed at the grain boundaries and in the matrix after deformation. According to the discussion, the hot working should be processed in the temperature range of 1050°C to 1150°C and in the strain rate range of 0.01 to 1 s−1.

Deformation Behavior and Microstructure Evolution of the Cu-2Ni-0.5Si-0.15Ag Alloy During Hot Compression

Hot deformation behavior of the Cu-2Ni-0.5Si-0.15Ag alloy was investigated by hot compression tests using the Gleeble-1500D thermo-simulator in the 873 K to 1073 K (600 °C to 800 °C) temperatures range with the 0.01 to 5 s−1 strain rate. The flow stress strongly depends on the deformation parameters, including temperature and strain rate. The flow stress decreases with the deformation temperature and increases with the strain rate. The constitutive relationship between the peak stress, the strain rate, and the deformation temperature can be described by the Zener–Hollomon Z parameter in the hyperbolic sine function with the hot deformation activation energy of 316 kJ/mol. The dynamic recrystallization (DRX) is one of the important softening mechanisms of the Cu-2Ni-0.5Si-0.15Ag alloy during hot deformation. The DRX behavior of the Cu-2Ni-0.5Si-0.15Ag alloy is strongly affected by the Z parameter. Lower Z parameter leads to more adequate DRX proceeding.

Hot Deformation Behavior of a Novel Ni-Cr-Mo-B Ultra-heavy Plate Steel by Hot Compression Test

Hot deformation behavior of a novel Ni-Cr-Mo-B heavy plate steel was studied by hot compression tests, which were conducted on a Gleeble-3800 thermo-mechanical simulator corresponding to the temperature range of 850–1150°C with the strain rates of 0. 01–10s−1 and the true strain of 0. 8. The results suggest that the majority of flow curves exhibit a typical dynamic recrystallization (DRX) behavior with an apparent single peak stress followed by a gradual fall towards a steady-state stress. Important characteristic parameters of flow behavior as critical stress/strain for initiation of DRX and peak and steady-state stress/strain were derived from curves of strain hardening rate versus stress and stress versus strain, respectively. Material constants of the investigated steel were determined based on Arrhenius-type constitutive equation, and then the peak stress was predicted by the equation with the hot deformation activation energy of 379 139 J/mol, and the predicted values agree well with the experimental values. Furthermore, the effect of Zener-Hollomon parameter on the characteristic points of flow curves was studied using the power law relation, and the ratio of critical stress and strain to peak stress and strain were found to be 0. 91 and 0.46, respectively.

Gas tungsten arc welding and friction stir welding of ultrafine grained AISI 304L stainless steel: Microstructural and mechanical behavior characterization

In the present study, an ultrafine grained (UFG) AISI 304L stainless steel with the average grain size of 650nm was successfully welded by both gas tungsten arc welding (GTAW) and friction stir welding (FSW). GTAW was applied without any filler metal. FSW was also performed at a constant rotational speed of 630rpm and different welding speeds from 20 to 80mm/min. Microstructural characterization was carried out by High Resolution Scanning Electron Microscopy (HRSEM) with Electron Backscattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM). Nanoindentation, microhardness measurements and tensile tests were also performed to study the mechanical properties of the base metal and weldments. The results showed that the solidification mode in the GTAW welded sample is FA (ferrite–austenite) type with the microstructure consisting of an austenite matrix embedded with lath type and skeletal type ferrite. The nugget zone microstructure in the FSW welded samples consisted of equiaxed dynamically recrystallized austenite grains with some amount of elongated delta ferrite. Sigma phase precipitates were formed in the region ahead the rotating tool during the heating cycle of FSW, which were finally fragmented into nanometric particles and distributed in the weld nugget. Also there is a high possibility that the existing delta ferrite in the microstructure rapidly transforms into sigma phase particles during the short thermal cycle of FSW. These suggest that high strain and deformation during FSW can promote sigma phase formation. The final austenite grain size in the nugget zone was found to decrease with increasing Zener–Hollomon parameter, which was obtained quantitatively by measuring the peak temperature, calculating the strain rate during FSW and exact examination of hot deformation activation energy by considering the actual grain size before the occurrence of dynamic recrystallization. Mechanical properties observations showed that the welding efficiency of the FSW welded sample is around 70%, which is more than 20% higher than the GTAW welded sample.