Hot Deformation and Processing Map of Pb-Mg-10Al-1B Alloy

The hot deformation behavior of the novel Pb-Mg-10Al-1B alloy has been investigated by hot compressive tests in the temperature range from 453 to 613 K within the strain rate range of 0.01-1 s^?1 using a Gleeble-1500 thermal simulator testing machine. The results show that the flow stress increases with increasing strain rate and decreasing temperature. The hot deformation behavior can be described by a constitutive equation with hyperbolic sine function or Zener-Hollomon parameter. The hot deformation activation energy of Pb-Mg-10Al-1B alloy is 151.2543 kJ/mol. The processing map at the strain of 0.4 exhibits an instable deformation domain of 460-520 K at 0.06-1 s^?1. According to the processing map, the optimum hot-working conditions for Pb-Mg-Al-B alloy are 573 K and 0.01 s^?1.     

Research on the Hot Deformation Behavior of Al-Zn-Mg-Sc-Zr Alloy During Compression at Elevated Temperature

The flow behavior of Al-Zn-Mg-Sc-Zr alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermo-mechanical equipment. Compression tests were performed in the temperature range of 340-500 °C and in the strain rate range of 0.001-10 s^?1.The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature, and decreases with increasing temperature at a given imposed strain rate. The relationship between flow stress and strain rate and temperature was derived by analyzing the experimental data. The constitutive equation of Al-Zn-Mg-Sc-Zr alloy during hot compression deformation can be described by the Arrhenius relationship of the hyperbolic sine form. The values of A, n, and α in the analytical expression of strain rate are fitted to be 1.49 × 10¹⁰ s^?1, 7.504, and 0.0114 MPa^?1, respectively. The hot deformation activation energy of the alloy during compression is 150.25 kJ/mol. The temperature and strain rate have great influences on microstructure evolution of Al-Zn-Mg-Sc-Zr alloy during hot compression deformation. According to microstructure evolution, the dynamic flow softening is mainly caused by dynamic recovery and dynamic recrystallization in this present experiment.     

Hot Compression Deformation Behavior and Processing Maps of Mg-Gd-Y-Zr Alloy

Hot compression deformation behavior and processing maps of the Mg-Gd-Y-Zr alloy were investigated in this paper. Compression tests were conducted at the temperature range from 300 to 450 °C and the strain rate range from 0.001 to 1.0 s^?1. It is found that the flow stress behavior is described by the hyperbolic sine constitutive equation in which the average activation energy of 251.96 kJ/mol is calculated. Through the flow stress behavior, the processing maps are calculated and analyzed according to the dynamic materials model. In the processing maps, the variation of the efficiency of the power dissipation is plotted as a function of temperature and strain rate. The instability domains of flow behavior are identified by the maps. The maps exhibit a domain of dynamic recrystallization occurring at the temperature range of 375-450 °C and strain rate range of 0.001-0.03 s^?1 which are the optimum parameters for hot working of the alloy.     

Hot Deformation Characteristics of GH625 and Development of a Processing Map

The hot deformation behavior of GH625 is investigated by a compression test in the temperature range of 950-1150 °C and the strain rate of 10^?3-5 s^?1. It is found that the flow stress behavior is described by the hyperbolic sine constitutive equation with average activation energy of 421 kJ/mol. Through the flow stresses’ curves, the processing maps are constructed and analyzed according to the dynamic materials model. In the processing map, the variation of the efficiency of the power dissipation is plotted as a function of temperature and strain rate, and the maps exhibit a significant feature with a domain of dynamic recrystallization occurring at the temperature range of 950-1150 °C and in the strain rate range of 0.005-0.13 s^?1, which are the optimum parameters for hot working of the alloy. Meanwhile, the instability zones of flow behavior can also be recognized by the maps.     

The Effect of Deformation Heating on Restoration and Constitutive Equation of a Wrought Equi-Atomic NiTi Alloy

In this study, a set of constitutive equation corrected for deformation heating is proposed for a near equi-atomic NiTi shape memory alloy using isothermal hot compression tests in temperature range of 700 to 1000 °C and strain rate of 0.001 to 1 s⁻¹. In order to determine the temperature rise due to deformation heating, Abaqus simulation was employed and varied thermal properties were considered in the simulation. The results of hot compression tests showed that at low pre-set temperatures and high strain rates the flow curves exhibit a softening, while after correction of deformation heating the softening is vanished. Using the corrected flow curves, the power-law constitutive equation of the alloy was established and the variation of constitutive constants with strain was determined. Moreover, it was found that deformation heating introduces an average relative error of about 9.5% at temperature of 800 °C and strain rate of 0.1 s⁻¹. The very good agreement between the fitted flow stress (by constitutive equation) and the measured ones indicates the accuracy of the constitutive equation in analyzing the hot deformation behavior of equi-atomic NiTi alloy.     

A Modified Constitutive Equation for Aluminum Alloy Reinforced by Silicon Carbide Particles at Elevated Temperature

In this paper, the constitutive relationship of an aluminum alloy reinforced by silicon carbide particles is investigated using a new method of double multivariate nonlinear regression (DMNR) in which the strain, strain rate, deformation temperature, and the interaction effect among the strain, strain rate, and deformation temperature are considered. The experimental true stress-strain data were obtained by isothermal hot compression tests on a Gleeble-3500 thermo-mechanical simulator in the temperature range of 623-773 K and the strain rate range of 0.001-10 s^?1. The experiments showed that the material-softening behavior changed with the strain rate, and it changed from dynamic recovery to dynamic recrystallization with an increase in the strain rate. A new constitutive equation has been established by the DMNR; the correlation coefficient (R) and average absolute relative error (AARE) of this model are 0.98 and 7.8%, respectively. To improve the accuracy of the model, separate constitutive relationships were obtained according to the softening behavior. At strain rates of 0.001, 0.01, 0.1, and 1 s^?1, the R and AARE are 0.9865 and 6.0%, respectively; at strain rates of 5 and 10 s^?1, the R and AARE are 0.9860 and 3.0%, respectively. The DMNR gives an accurate and precise evaluation of the flow stress for the aluminum alloy reinforced by silicon carbide particles.     

纯铂的热塑性变形行为及微观结构演变规律研究

用热模拟试验机研究了纯铂在真应变量为0.9、变形温度为550℃～950℃和应变速率为0.01～1 s~(-1)的热塑性变形行为,并对热压缩后的样品进行了金相观察和显微硬度测量。结果表明,纯铂的流变应力随变形温度的升高和应变速率的降低而降低;其热压缩变形过程中软化行为由变形温度和变形速率共同作用决定,一般以动态回复为主,而在低应变速率和高形变温度下以动态再结晶为主,动态再结晶发生造成的软化使纯铂样品的硬度迅速下降。利用Zener-Hollomon参数方程获得了热塑性变形流变应力本构方程,得到纯铂的热变形激活能为208.51 kJ/mol,流变应力拟合公式计算值与实验值的平均误差为5.9%。     

Modeling the High Temperature Flow Behavior and Dynamic Recrystallization Kinetics of a Medium Carbon Microalloyed Steel

In this study, the hot deformation behavior of a medium carbon microalloyed steel was investigated. The hot compression test was conducted in the temperature range of 1000-1200 °C under strain rates of 0.01, 0.1 and 1 s^?1. It has been observed that the flow stress increases with a decrease in temperature and/or an increase in strain rate. Furthermore, dynamic recrystallization (DRX) is found to be the main flow softening mechanism in almost all deformation conditions. Material parameters of the constitutive equations are found to be strain dependent. Their relationship with strain is identified by a fourth order polynomial fit. Then, a constitutive model is developed to predict the flow stress of the material incorporating the strain softening effect. The accuracy of the proposed model for the flow stress is evaluated by applying the absolute average error method. The result of 6.08% indicates a good agreement between predicted and experimental data. Moreover, the critical characteristics of DRX are extracted from the stress-strain curves at different deformation conditions. It is found that by increasing the strain rate at a constant temperature or decreasing deformation temperature under a constant strain rate, the recrystallization curve shifts to the higher strains. The kinetics of DRX increases with increasing deformation temperature or strain rate.     

Arrhenius-Type Constitutive Model for High Temperature Flow Stress in a Nickel-Based Corrosion-Resistant Alloy

Hot deformation behavior of Nickel-based corrosion-resistant alloy (N08028) was studied in compression tests conducted in the temperature range of 1050-1200 °C and the strain rate range of 0.001-1 s^?1. The flow stress behavior and microstructural evolution were observed during the hot deformation process. The results show that the flow stress increases with deformation temperature decreasing and strain rate increasing, and that the deformation activation energy (Q) is not a constant but increases with strain rate increasing at a given strain, which is closely related with dislocation movement. On this basis, a revised strain-dependent hyperbolic sine constitutive model was established, which considered that the “material constants” in the original model vary as functions of the strain and strain rate. The flow curves of N08028 alloy predicted by the proposed model are in good agreement with the experimental results, which indicates that the revised constitutive model can estimate precisely the flow curves of N08028 alloy.     

Constitutive relationship of IN690 superalloy by using uniaxial compression tests

The hot deformation behavior of IN690 superalloy was characterized in a temperature range of 1273-1473 K and a strain rate range of 0.01-10 s-1 using uniaxial compression tests on process annealed material.The constitutive relations between flow stress and effective strain,effective strain rate as well as deformation temperature were studied.It can be concluded that the flow stress significantly reduces with the deformation temperature of IN690 superalloy increasing.Whereas,there is a significant increase of flow stress when the strain rate increases from 0.1 s-1 to 10 s-1.Based on the hyperbolic-sine Arrhenius-type equation,a constitutive equation considering compensation of strain was developed.The activation energy and the material constants(Q,n and ln A) decrease as the deformation strain increases.The strain dependent term is successfully incorporated in the constitutive equation through a quartic equation.A good agreement between the experimental data and the predicted results has been achieved,indicating that the proposed constitutive equation and the methods of determing the material constants are suitable to model the high temperature deformation behavior of IN690 superalloy.     

Flow Behavior and Constitutive Equation of Ti-6.5Al-2Sn-4Zr-4Mo-1W-0.2Si Titanium Alloy

In order to get a reliable constitutive equation for the finite element simulation, flow behavior of Ti-6.5Al-2Sn-4Zr-4Mo-1W-0.2Si alloy under high temperature was investigated by carrying a series of isothermal compression tests at temperatures of 1153-1293 K and strain rates of 0.01-10.0 s^?1 on the Gleeble-1500 simulator. Results showed that the true stress-strain curves exhibited peaks at small strains, after which the flow stress decreased monotonically. Ultimately, the flow curves reached steady state at the strain of 0.6, showing a dynamic flow softening phenomenon. The effects of strain rate, temperature, and strain on the flow behavior were researched by establishing a constitutive equation. The relations among stress exponent, deformation activation energy, and strain were preliminarily discussed by using strain rate sensitivity exponent and dynamic recrystallization kinetics curve. Stress values predicted by the modified constitutive equation showed a good agreement with the experimental ones. The correlation coefficient (R) and average absolute relative error (AARE) were 98.2% and 4.88%, respectively, which confirmed that the modified constitutive equation could give an accurate estimation of the flow stress for BT25y titanium alloy.     

Flow stress and dynamic recrystallization behavior of Al-9Mg-1.1Li-0.5Mn alloy during hot compression process

The flow stress behavior of spray-formed Al-9Mg-1.1Li-0.5Mn alloy was studied using thermal simulation tests on a Gleeble-3500 machine over deformation temperature range of 300-450 °C and strain rate of 0.01-10 s^?1. The microstructural evolution of the alloy during the hot compression process was characterized by transmission electron microscopy (TEM) and electron back scatter diffractometry (EBSD). The results show that the flow stress behavior and microstructural evolution are sensitive to deformation parameters. The peak stress level, steady flow stress, dislocation density and amount of substructures of the alloy increase with decreasing deformation temperature and increasing strain rate. Conversely, the high angle grain boundary area increases, the grain boundary is in serrated shape and the dynamic recrystallization in the alloy occurs. The microstructure of the alloy is fibrous-like and the main softening mechanism is dynamic recovery during steady deformation state. The flow stress behavior can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation with the hot deformation activation energy of 184.2538 kJ/mol. The constitutive equation and the hot processing map were established. The hot processing map exhibits that the optimum processing conditions for Al-9Mg-1.1Li-0.5Mn alloy are in deformation temperature range from 380 to 450 °C and strain rate range from 0.01 to 0.1 s^?1.     

The Use of ANN to Predict the Hot Deformation Behavior of AA7075 at Low Strain Rates

In this study, artificial neural network (ANN) was used to model the hot deformation behavior of 7075 aluminum alloy during compression test, in the strain rate range of 0.0003-1 s^?1 and temperature range of 200-450 °C. The inputs of the model were temperature, strain rate, and strain, while the output of the model was the flow stress. The feed-forward back-propagation network with two hidden layers was built and successfully trained at different deformation domains by Levenberg-Marquardt training algorithm. Comparative analysis of the results obtained from the hyperbolic sine, the power law constitutive equations, and the ANN shows that the newly developed ANN model has a better performance in predicting the hot deformation behavior of 7075 aluminum alloy.     

Microstructure evolution and hot deformation behavior of Cu−3Ti−0.1Zr alloy with ultra-high strength

The hot compression deformation behavior of Cu–3Ti–0.1Zr alloy with the ultra-high strength and good electrical conductivity was investigated on a Gleeble–3500 thermal-mechanical simulator at temperatures from 700 to 850 °C with the strain rates between 0.001 and 1 s⁻¹. The results show that work hardening, dynamic recovery and dynamic recrystallization occur in the alloy during hot deformation. The hot compression constitutive equation at a true strain of 0.8 is constructed and the apparent activation energy of hot compression deformation Q is about 319.56 kJ/mol. The theoretic flow stress calculated by the constructed constitutive equation is consistent with the experimental result, and the hot processing maps are established based on the dynamic material model. The optimal hot deformation temperature range is between 775 and 850 °C and the strain rate range is between 0.001 and 0.01 s⁻¹.     

Hot Deformation Characteristics of 13Cr-4Ni Stainless Steel Using Constitutive Equation and Processing Map

Hot compression tests were performed to study the hot deformation characteristics of 13Cr-4Ni stainless steel. The tests were performed in the strain rate range of 0.001-10 s^?1 and temperature range of 900-1100 °C using Gleeble® 3800 simulator. A constitutive equation of Arrhenius type was established based on the experimental data to calculate the different material constants, and average value of apparent activation energy was found to be 444 kJ/mol. Zener-Hollomon parameter, Z, was estimated in order to characterize the flow stress behavior. Power dissipation and instability maps developed on the basis of dynamic materials model for true strain of 0.5 show optimum hot working conditions corresponding to peak efficiency range of about 28-32%. These lie in the temperature range of 950-1025 °C and corresponding strain rate range of 0.001-0.01 s^?1 and in the temperature range of 1050-1100 °C and corresponding strain rate range of 0.01-0.1 s^?1. The flow characteristics in these conditions show dynamic recrystallization behavior. The microstructures are correlated to the different stability domains indicated in the processing map.     

Optimization of thermal processing parameters of Ti555211 alloy using processing maps based on Murty criterion

Isothermal compression testing of Ti555211 titanium alloys was carried out at deformation temperatures from 750 to 950 °C in 50 °C intervals with a strain rate of0.001–1.000 s~(-1). The high-temperature deformation behavior of the Ti555211 alloy was characterized by analysis of stress–strain behavior, kinetics and processing maps. A constitutive equation was formulated to describe the flow stress as a function of deformation temperature and strain rate, and the calculated apparent activation energies are found to be 454.50 and 207.52 k J mol~(-1)in the a b-phase and b-phase regions, respectively. A processing map based on the Murty instability criterion was developed at a strain of 0.7. The maps exhibit two domains of peak efficiency from 750 to 950 °C. A *60 % peak efficiency occurs at 800–850 °C/0.001–0.010 s~(-1). The other peak efficiency of *60 % occurs at C950 °C/0.001–0.010 s~(-1), which can be considered to be the optimum condition for high-temperature working of this alloy.However, at strain rates of higher than 1.000 s~(-1)and deformation temperatures of 750 and 950 °C, clear process flow lines and bands of flow localization occur in the hightemperature deformation process, which should be avoided in Ti555211 alloy hot processing. The mechanism in stability domain and instability domain was also discussed.     

Physical Simulation of Hot Deformation of Low-Carbon Ti-Nb Microalloyed Steel and Microstructural Studies

Constitutive equations for the flow behavior of a 0.13 pct C-1.52 pct Mn-0.28 pct Si-0.05 pct Nb-0.052 pct Ti microalloyed steel are determined. For this purpose, uniaxial hot compression tests were performed over a wide range of strain rates (0.01 to 80 s^?1) and temperatures (750 to 1050 °C). From microstructural observations, the physical processes that occurred during deformation are discussed and related to the stress-strain responses. Using sinh type constitutive equation, the average apparent activation energy for hot deformation is obtained as 359 kJ/mol. The processing map obtained using the power dissipation efficiency, η, correlates well with microstructural changes observed. In the temperature range of 825-1050 °C and strain rate range of 0.01-0.1 s^?1, the strain rate sensitivity map and the power dissipation map exhibit a peak domain wherein dynamic recrystallization is the primary restoration mechanism. Safe domains of strain, strain rate, and temperature for hot working of this steel have been identified.     

Cu-Ni-Si-P合金热变形行为及热加工图

采用高温等温压缩试验,对Cu?Ni?Si?P合金在应变速率0.01~5?1、变形温度600~800°C条件下的高温变形行为进行了研究,得出了该合金热压缩变形时的热变形激活能Q和本构方程。根据实验数据与热加工工艺参数构建了该合金的热加工图,利用热加工图对该合金在热变形过程中的热变形工艺参数进行了优化,并利用热加工图分析了该合金的高温组织变化。热变形过程中Cu?Ni?Si?P合金的流变应力随着变形温度的升高而降低,随着应变速率的提高而增大,该合金的动态再结晶温度为700°C。该合金热变形过程中的热变形激活能Q为485.6 kJ/mol。通过分析合金在应变为0.3和0.5时的热加工图得出该合金的安全加工区域的温度为750~800°C,应变速率为0.01~0.1 s?1。通过合金热变形过程中高温显微组织的观察,其组织规律很好地符合热加工图所预测的组织规律。