In engineering practice,it is often necessary to determine functional relationships between dependent and independent variables.These relationships can be highly nonlinear,and classical regression approaches cannot al...In engineering practice,it is often necessary to determine functional relationships between dependent and independent variables.These relationships can be highly nonlinear,and classical regression approaches cannot always provide sufficiently reliable solutions.Nevertheless,Machine Learning(ML)techniques,which offer advanced regression tools to address complicated engineering issues,have been developed and widely explored.This study investigates the selected ML techniques to evaluate their suitability for application in the hot deformation behavior of metallic materials.The ML-based regression methods of Artificial Neural Networks(ANNs),Support Vector Machine(SVM),Decision Tree Regression(DTR),and Gaussian Process Regression(GPR)are applied to mathematically describe hot flow stress curve datasets acquired experimentally for a medium-carbon steel.Although the GPR method has not been used for such a regression task before,the results showed that its performance is the most favorable and practically unrivaled;neither the ANN method nor the other studied ML techniques provide such precise results of the solved regression analysis.展开更多
The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion a...The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion at 1150℃(A3).The results show that A2 sample,extruded at 1100℃ with uniform γ+γ′duplex microstructures,demonstrates excellent hot deformation behavior at both 1050 and 1100℃.The true stress-true strain curves of A2 sample maintain a hardening-softening equilibrium over a larger strain range,with post-deformation average grain size of 5μm.The as-HIPed A1 sample and 1150℃ extruded A3 sample exhibit a softening region in deformation curves at 1050℃,and the grain microstructures reflect an incomplete recrystallized state,i.e.combination of fine recrystallized grains and initial larger grains,characterized by a necklace-like microstructure.The predominant recrystallization mechanism for these samples is strain-induced boundary migration.At 1150℃ with a strain rate of 0.001 s^(-1),the influence of the initial microstructure on hot deformation behavior and resultant microstructure is relatively less pronounced,and postdeformation microstructures are fully recrystallized grains.Fine-grained microstructures are conducive to maximizing the hot deformation potential of alloy.By judiciously adjusting deformation regimes,a fine and uniform deformed microstructure can be obtained.展开更多
Using a Gleeble 3500 thermomechanical simulation testing machine,the hot deformation characteristics of 23Cr-8Ni steel were investigated under the conditions of 1000–1250℃ and 0.001‒10 s^(−1).Furthermore,the microst...Using a Gleeble 3500 thermomechanical simulation testing machine,the hot deformation characteristics of 23Cr-8Ni steel were investigated under the conditions of 1000–1250℃ and 0.001‒10 s^(−1).Furthermore,the microstructure of the characterization region was analyzed to investigate the recrystallization behavior of 23Cr-8Ni steel.Results show that as the strain rate decreases and the deformation temperature increases,the flow stress decreases.Because the softening phenomenon occurs after the peak stress,the flow stress decreases.The stress index(n)is 4.28,and the thermal deformation activation energy(Q)is 588878 J/mol.Processing map is established,and an optimal thermal processing range of 0.001–0.1 s^(−1) and 1000–1200℃ is achieved,therefore greatly promoting the yield rate.展开更多
The popular constitutive models used in the field of hot forming of magnesium alloys can be divided into phenomenological models,machine learning models,and internal state variables(ISV)models based on physical mechan...The popular constitutive models used in the field of hot forming of magnesium alloys can be divided into phenomenological models,machine learning models,and internal state variables(ISV)models based on physical mechanisms.Currently,there is a lack of comparison and evaluation regarding the suitability of different types of models.In this study,Mg-Gd-Y-Zr alloy is taken as the research object.The hot deformation behavior of the alloy was studied systematically.Subsequently,Arrhenius model with strain compensation,artificial neural network(ANN)model,and ISV model involving dynamic recrystallization(DRX),dislocation density and grain size evolution were established.ANN model demonstrates a higher level of accuracy in fitting the original stress-strain curves compared to both ISV model and modified Arrhenius model,but ANN model is not suitable for predicting the experimental results outside of the initial database.ISV model considers the impact of microstructure evolution history on stress,making it highly effective in reflecting the mechanical responses under complex loading condition.The established ISV model is embedded in the ABAQUS software,which shows good ability in calculating the mechanical response,dimension,and microstructure evolution information of the component during hot forming.展开更多
As high-speed railway transportation advances toward increased velocities,it is imperative to enhance the mechanical performance of EA4T axle steel,especially through microstructures regulation by thermal–mechanical ...As high-speed railway transportation advances toward increased velocities,it is imperative to enhance the mechanical performance of EA4T axle steel,especially through microstructures regulation by thermal–mechanical processing.However,little research has been conducted on the phase transformation and microstructure evolution mechanism of EA4T steel under thermal–mechanical load,resulting in a lack of theoretical guidance.The hot deformation behavior and phase transformation mechanism of EA4T steel were investigated under different conditions of strain rates(0.01–10 s^(−1))and temperatures(850–1200℃).A relation of deformation stresses with Zener–Hollomon parameter was established to characterize the mechanical response and dynamic softening effect of EA4T steel during hot compression.The evolution of grain boundaries with different misorientations has been analyzed to evaluate the influence of strain rates and temperatures on the dynamic recrystallization.It was found that the grain refinement mechanisms of EA4T steel by dynamic recrystallization including twin-assisted boundary bulging,sub-grain rotation,and sub-grain growth.Transmission electron microscopy observations confirmed that dynamic recrystallization nuclei and small recrystallized grains impeded martensite phase nucleation during hot deformation,while the ongoing dynamic recrystallization consumed deformation stored energy and reduced dislocation density,which mitigated the stress concentration in the parent phase of martensite,thereby facilitating the uniform growth of martensite lath with a mixing structure of nanotwins and dislocations during quenching.展开更多
The hot deformation behavior of magnesium(Mg)alloys is significantly governed by the multi-physics coupling effects of temperature(T),strain rate(ε)and strain(ε),resulting in flow behavior that exhibits pronounced n...The hot deformation behavior of magnesium(Mg)alloys is significantly governed by the multi-physics coupling effects of temperature(T),strain rate(ε)and strain(ε),resulting in flow behavior that exhibits pronounced nonlinearity and multi-scale complexity.This study systematically investigates the hot deformation behavior of Mg-Y-Nd-(Sm)-Zr alloys.Sm alloying promotes recrystallization.The flow stress of Sm-containing alloys declines sharply towards a steady state after reaching its peak value.To overcome the limitations of the Arrhenius-type constitutive(AC)model in predicting complex nonlinear flow behavior,the AC and data hybrid informed neural network(ACINN)model is developed.This approach enhances the predictive accuracy and extends the applicability of the traditional AC model.The evolution of microstructure and recrystallization behavior under hot deformation conditions are investigated based on results from electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).The relationship between the power dissipation factor(η)and recrystallization behavior is further examined using K-means clustering analysis.The results demonstrate that dynamic recrystallization(DRX)behavior varies with theηvalue,comprising four distinct regimes:dynamic recovery(DRV),discontinuous dynamic recrystallization(DDRX)dominance,continuous dynamic recrystallization(CDRX)dominance and complete dynamic recrystallization.This analysis presents a new perspective for studying the hot deformation processes of Mg alloys.展开更多
The hot deformation behavior and microstructure evolution of 1460 Al-Li alloy were investigated by isothermal compression test conducted at various strain rates（10-3-10 s-1） and temperatures（573-773 K）. The flow s...The hot deformation behavior and microstructure evolution of 1460 Al-Li alloy were investigated by isothermal compression test conducted at various strain rates（10-3-10 s-1） and temperatures（573-773 K）. The flow stress curves were corrected by considering the friction at the platen/specimen interface and the temperature change due to the deformation heating. The effects of strain, strain rate and temperature on the deformation behavior were characterized by the Zener-Hollomon parameter in a hyperbolic-sine equation, and the constitutive equations were established according to the peak flow stress associated with dynamic recovery, dynamic recrystallization and the dissolution of T1 phases. In the entire strain rate and temperature range, the prediction capabilities of the developed constitutive equation are proved to be feasible and effective with a linear correlation coefficient and an average absolute relative error coefficient of 0.9909 and 6.72%, respectively.展开更多
The hot deformation behavior of AA2014forging aluminum alloy was investigated by isothermal compression tests attemperatures of350-480°C and strain rates of0.001-1s-1on a Gleeble-3180simulator.The corresponding m...The hot deformation behavior of AA2014forging aluminum alloy was investigated by isothermal compression tests attemperatures of350-480°C and strain rates of0.001-1s-1on a Gleeble-3180simulator.The corresponding microstructures of thealloys under different deformation conditions were studied using optical microscopy(OM),electron back scattered diffraction(EBSD)and transmission electron microscopy(TEM).The processing maps were constructed with strains of0.1,0.3,0.5and0.7.The results showed that the instability domain was more inclined to occur at strain rates higher than0.1s-1and manifested in theform of local non-uniform deformation.At the strain of0.7,the processing map showed two stability domains:domain I(350-430°C,0.005-0.1s-1)and domain II(450-480°C,0.001-0.05s-1).The predominant softening mechanisms in both of the twodomains were dynamic recovery.Uniform microstructures were obtained in domain I,and an extended recovery occurred in domainII,which would lead to the potential sub-grain boundaries progressively transforming into new high-angle grain boundaries.Theoptimum hot working parameters for the AA2014forging aluminum alloy were determined to be370-420°C and0.008-0.08s-1.展开更多
The hot compression behavior of as-extruded Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy was studied on a Gleeble-3500 thermal simulation machine.Experiments were conducted at temperatures ranging from 523 to 673 K and strain rat...The hot compression behavior of as-extruded Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy was studied on a Gleeble-3500 thermal simulation machine.Experiments were conducted at temperatures ranging from 523 to 673 K and strain rates ranging from 0.001 to 1 s^(-1).Results showed that an increase in the strain rate or a decrease in deformation temperature led to an increase in true stress.The constitutive equation and processing maps of the alloy were obtained and analyzed.The influence of deformation temperatures and strain rates on microstructural evolution and texture was studied with the assistance of electron backscatter diffraction(EBSD).The as-extruded alloy exhibited a bimodal structure that consisted of deformed coarse grains and fine equiaxed recrystallized structures(approximately 1.57μm).The EBSD results of deformed alloy samples revealed that the recrystallization degree and average grain size increased as the deformation temperature increased.By contrast,dislocation density and texture intensity decreased.Compressive texture weakened with the increase in the deformation temperature at the strain rate of 0.01 s-1.Most grains with{0001}planes tilted away from the compression direction(CD)gradually.In addition,when the strain rate decreased,the recrystallization degree and average grain size increased.Meanwhile,the dislocation density decreased.Texture appeared to be insensitive to the strain rate.These findings provide valuable insights into the hot compression behavior,microstructural evolution,and texture changes in the Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy,contributing to the understanding of its processing-microstructure-property relationships.展开更多
Hot deformation behavior of the Cu-Cr-Zr alloy was investigated using hot compressive tests in the tem- perature range of 650-850℃ and strain rate range of 0.001-10 s-1. The constitutive equation of the alloy based o...Hot deformation behavior of the Cu-Cr-Zr alloy was investigated using hot compressive tests in the tem- perature range of 650-850℃ and strain rate range of 0.001-10 s-1. The constitutive equation of the alloy based on the hyperbolic-sine equation was established to characterize the flow stress as a function of strain rate and deformation temperature. The critical conditions for the occurrence of dynamic recrystallization were determined based on the alloy strain hardening rate curves. Based on the dynamic material model, the processing maps at the strains of 0.3, 0.4 and 0.5 were obtained. When the true strain was 0.5, greater power dissipation efficiency was observed at 800-850 ℃ and under 0.001-0.1 s-1, with the peak efficiency of 47%. The evolution of DRX microstructure strongly depends on the deformation temperature and the strain rate. Based on the processing maps and microstructure evolution, the optimal hot working conditions for the Cu-Cr-Zr alloy are in the temperature range of 800-850 ℃ and the strain rate range of 0.001-0.1 s-1.展开更多
Hot compression tests in the temperature range of 340-450 ℃ and strain rate range of 0.001-1 s^-1 of spray-formed 7055 aluminum alloy were carried out to study its hot deformation behavior. Three phenomenological mod...Hot compression tests in the temperature range of 340-450 ℃ and strain rate range of 0.001-1 s^-1 of spray-formed 7055 aluminum alloy were carried out to study its hot deformation behavior. Three phenomenological models including Johnson-Cook, modified Fields-Backofen and Arrhenius-type were introduced to predict the flow stresses during the compression process. And then, a comparative predictability of the phenomenological models was estimated in terms of the relative errors, correlation coefficient（R）, and average absolute relative error（AARE）. The results indicate that Johnson-Cook model and modified Fields-Backofen model cannot well predict the hot deformation behavior due to the large deviation in the process of line regression fitting. Arrhenius-type model obtains the best fit through combining the effect of strain rate and temperature.展开更多
Q345E as one of typical low alloy steels is widely used in manufacturing basic components in many fields because of its eminent formability under elevated temperature. In this work, the deformation behavior of Q345E s...Q345E as one of typical low alloy steels is widely used in manufacturing basic components in many fields because of its eminent formability under elevated temperature. In this work, the deformation behavior of Q345E steel was investigated by hot compression experiments on Gleeble-3500 thermo-mechanical simulator with the temperature ranging from 850 ℃ to 1150 ℃ and strain rate ranging from 0.01 s-1 to 10 s-1. The experimental results indicate that dynamic softening of Q345E benefits from increasing deformation temperature and decreasing strain rate. The mathematical relationship between dynamic softening degree and deformation conditions is established to predict the dynamic softening degree quantitatively, which is further proved by some optical microstructures of Q345E. In addition, the experimental results also reveal that the stress level decreases with increasing deformation temperature and decreasing strain rate. The constitutive equation for flow stress of Q345E is formulated by Arrihenius equation and the modified Zener-Hollomon parameter considering the compensation of both strain and strain rate. The flow stress values predicted by the constitutive equation agree well with the experimental values, realizing the accurate prediction of the flow stress of Q345E steel under hot deformation.展开更多
The hot deformation behavior of Ti22A125 Nb was investigated by hot compression test.The flow stressstrain curves can be divided into two types：conventional dynamic recrystallization（DRX） and discontinuous DRX.The ...The hot deformation behavior of Ti22A125 Nb was investigated by hot compression test.The flow stressstrain curves can be divided into two types：conventional dynamic recrystallization（DRX） and discontinuous DRX.The different softening mechanism and micro structure observation of conventional DRX and discontinuous DRX were analyzed.The processing map（PM） of Ti22A125 Nb was built to predict the safe deformation region.The optimal low strain rate domain（DOM I） with high power dissipation efficiency indicates the complete DRX.Additionally,in the high strain rate and low-temperature domain（DOM Ⅲ）,the power dissipation efficiency is low and some adiabatic shear bands and glide bands are observed,which are unsafe and should be avoided.Finally,the DRX map was established.In DOM I,it reveals low dislocation density and high DRX content,which is in agreement with PM.展开更多
Hot deformation behavior and microstructural evolution of as-homogenized 7A65 Al alloy under isothermal compression at temperatures of 573-713 K and strain rates of 0.1-10.0 s-1were investigated.It was found that the ...Hot deformation behavior and microstructural evolution of as-homogenized 7A65 Al alloy under isothermal compression at temperatures of 573-713 K and strain rates of 0.1-10.0 s-1were investigated.It was found that the flow stress of 7A65 Al alloy exhibited a typical dynamic recovery characteristic at high-temperature deformation conditions,and a sixth-order polynomial strain compensated Arrhenius constitutive equation was proposed to describe the flow behavior.Based on the dynamic material model and the Prasad standard,the hot processing map was established.The optimal processing conditions were within the temperature range of 633-713 K and the strain rate range of 0.1-0.5 s^(-1)when the true strain exceeded 0.6.Deformation temperature and strain rate had an obvious effect on the micros tructure evolution of 7A65Al alloy,and the deformed microstructures were mainly composed of deformed grains and recovery structure.The main softening mechanism was dynamic recovery at the temperature of 573-713 K and the strain rate of 0.1-10.0s-1,but dynamic recrystallization was enhanced with the increase in temperature.展开更多
The hot deformation behavior of S31042 austenitic heat-resistant steel was investigated over the tempera- ture range of 900--1 200 ℃ and strain rate range of 0.01--10 s- 1 using hot compression tests and the correspo...The hot deformation behavior of S31042 austenitic heat-resistant steel was investigated over the tempera- ture range of 900--1 200 ℃ and strain rate range of 0.01--10 s- 1 using hot compression tests and the corresponding flow curves were obtained. The hot deformation activation energy of the test steel is 625 kJ/mol. The hot deformation equation and the relationship between the peak stresses, deformation temperature and strain rate were set up. The Zener-Hollomon parameter under various conditions was determined. The relation between the Zener-Hollomon parameter and the microstructure evolution of test steel was discussed. With the decrease of Zener-Hollomon param- eter, the microstructure of test steel transforms from deformation instability to dynamic recovery, partial dynamic recrystallization, full dynamic recrystallization with equiaxial structure, and finally to full dynamic recrystaUization with mixed crystal structure. The deformation condition can be adjusted easily by utilizing the Zener-Hollomon pa- rameter to obtain equiaxial microstructure.展开更多
The isothermally compression deformation behavior of an elevated Cu/Li weight ratio Al–Cu–Li alloy was investigated under various deformation conditions.The isothermal compression tests were carried out in a tempera...The isothermally compression deformation behavior of an elevated Cu/Li weight ratio Al–Cu–Li alloy was investigated under various deformation conditions.The isothermal compression tests were carried out in a temperature range from 300 to 500℃ and at a strain rate range from 0.001 to 10 s^-1.The results show that the peak stress level decreases with temperature increasing and strain rate decreasing,which is represented by the Zener–Hollomon parameter Z in the hyperbolic sine equation with the hot deformation activation energy of 218.5 k J/mol.At low Z value,the dynamic recrystallized grain is well formed with clean high-angle boundaries.At high Z value,a high dislocation density with poorly developed cellularity and considerable fine dynamic precipitates are observed.Based on the experimental data and dynamic material model,the processing maps at strain of 0.3,0.5 and 0.7 were developed to demonstrate the hot workability of the alloy.The results show that the main softening mechanism at high Z value is precipitate coarsening and dynamic recovery;the dynamic recrystallization of the alloy can be easily observed as ln Z ≤ 29.44,with peak efficiency of power dissipation of around 70%.At strains of 0.3,0.5 and 0.7,the flow instability domains are found at higher strain rates,which mainly locate at the upper part of processing maps.In addition,when the strain rate is 0.001 or 0.02 s^-1,there is a particular instability domain at 300–350℃.展开更多
Graphene nanoplates(GNPs)-reinforced magnesium matrix composites have been attracted great attention.However,knowledge is lack for the hot deformation behavior of GNP-reinforced magnesium(GNPs/Mg)composite.In this stu...Graphene nanoplates(GNPs)-reinforced magnesium matrix composites have been attracted great attention.However,knowledge is lack for the hot deformation behavior of GNP-reinforced magnesium(GNPs/Mg)composite.In this study,the fine-grained GNPs/Mg composite was fabricated by powder metallurgy process followed by extrusion.The hot deformation behavior,microstructure evolution and dynamic recrystallization(DRX)mechanism of fine-grained GNPs/Mg composite were investigated by hot compression test and electron back-scatter diffraction(EBSD).The hot compression tests of the composite were conducted at temperatures between 423 and 573 K with the strain rates from 0.001 to 1 s^(-1).The strain compensated power law equation was established to describe the hot deformation behavior of the composites.The stress exponent and activation energy of the composite are 7.76 and 83.23 kJ/mol,respectively,suggesting that the deformation mechanism is grain boundary slip controlled dislocation climb creep.The abnormally high stress exponent and activation energy are unattainable in the composite due to the fine grain size of the composites and the absence of Zener pinning and Orowan effects of GNPs reinforcement.The grain size increases with the decrease in Zener-Hollomn(Z)parameter,which can be well fitted by power-law relationship.With the increase in grain size and decrease in Z parameter,the geometrically necessary dislocation density decreases,which shows the approximately power-law relationship.A random and weak texture was formed after hot compression.The discontinuous dynamic recrystallization and continuous dynamic recrystallization mechanism dominated the DRX behavior at 473 K/0.001 s^(-1) and 573 K/0.001 s^(-1),respectively.展开更多
The isothermal compression test for Ti-6Al-7Nb alloy was conducted by using Gleeble-3800 thermal simulator.The hot deformation behavior of Ti-6Al-7Nb alloy was investigated in the deformation temperature ranges of 940...The isothermal compression test for Ti-6Al-7Nb alloy was conducted by using Gleeble-3800 thermal simulator.The hot deformation behavior of Ti-6Al-7Nb alloy was investigated in the deformation temperature ranges of 940-1030℃and the strain rate ranges of 0.001-10 s^(-1).Meanwhile,the activation energy of thermal deformation was computed.The results show that the flow stress of Ti-6Al-7Nb alloy increases with increasing the strain rate and decreasing the deformation temperature.The activation energy of thermal deformation for Ti-6Al-7Nb alloy is much greater than that for self-diffusion ofα-Ti andβ-Ti.Considering the influence of strain on flow stress,the strain-compensated Arrhenius constitutive model of Ti-6Al-7Nb alloy was established.The error analysis shows that the model has higher accuracy,and the correlation coefficient r and average absolute relative error are 0.9879 and 4.11%,respectively.The processing map(PM)of Ti-6Al-7Nb alloy was constructed by the dynamic materials model and Prasad instability criterion.According to PM and microstructural observation,it is found that the main form of instability zone is local flow,and the deformation mechanisms of the stable zone are mainly superplasticity and dynamic recrystallization.The optimal processing parameters of Ti-6Al-7Nb alloy are determined as follows:960-995℃/0.01-0.18 s^(-1)and 1000-1030℃/0.001-0.01 s^(-1).展开更多
The true stress-true strain curves of Ti-6Al-2Zr-IMO-IV alloy with hydrogen were obtained by hot compression test. The microstructures of the alloy before and after thermo-compression were observed. The apparent activ...The true stress-true strain curves of Ti-6Al-2Zr-IMO-IV alloy with hydrogen were obtained by hot compression test. The microstructures of the alloy before and after thermo-compression were observed. The apparent activation energies of deformation were calculated for the alloy with and without hydrogen. The behavior and mechanism of deformation for hydrogenated Ti-6A1-2Zr-IMO-IV alloy at high temperature were analyzed. The relationship between hydrogenation time and hydrogen content at 800 ℃ can be expressed as the equation： CH（t）=1.2-1.2exp（-t/120）. The true stress-true strain curves of hot compression for Ti-6Al-2Zr-IMO-IV alloy with hydrogen first move down and then move up as hydrogen content increases. Appropriate hydrogen content can reduce the peak of flow stress to minimal value. The apparent activation energies of deformation of the alloy with 0.47% hydrogen content and without hydrogen were calculated as 140 kJ·mol^-1 and 390 kJ-mol^-1, respectively, at 800 ℃ and at strain rate 8.3×10^4 s^-1. The apparent activation energy of deformation increases when the strain rate enhances from 8.3×10^-4 s^-1 to 8.3×10^-2 s^-1.展开更多
The hot deformation behavior of a newly developed Ni–W–Cr superalloy for use in 800℃molten salt reactors(MSRs)was looked into by isothermal compression tests in the temperature range of 1050–1200℃with a strain ra...The hot deformation behavior of a newly developed Ni–W–Cr superalloy for use in 800℃molten salt reactors(MSRs)was looked into by isothermal compression tests in the temperature range of 1050–1200℃with a strain rate of 0.001–1 s^(−1)under a true strain of 0.693.An Arrhenius-type model for the Ni–W–Cr superalloy was constructed by fitting the corrected flow stress data.In this model,the effect of dispersion of solid solution elements during thermal deformation on microstructure evolution was considered,as well as the effects of friction and adiabatic heating on the temperature and strain rate-dependent variation of flow stresses.The hot deformation activation energy of the Ni–W–Cr superalloy was 323 kJ/mol,which was less than that of the Hastelloy N alloy(currently used in MSRs).According to the rectified flow stress data,processing maps were created.In conjunction with the corresponding deformation microstructures,the flow instability domains of the Ni–W–Cr superalloy were determined to be 1050–1160℃/0.03–1 s^(−1)and 1170–1200℃/0.001–0.09 s^(−1).In these deformation conditions,a locally inhomogeneous microstructure was caused by flow-i.e.,incomplete dynamic recrystallization and hot working parameters should avoid sliding into these domains.The ideal processing hot deformation domain for the Ni–W–Cr superalloy was determined to be 1170–1200℃/0.6–1 s^(−1).展开更多
基金supported by the SP2024/089 Project by the Faculty of Materials Science and Technology,VˇSB-Technical University of Ostrava.
文摘In engineering practice,it is often necessary to determine functional relationships between dependent and independent variables.These relationships can be highly nonlinear,and classical regression approaches cannot always provide sufficiently reliable solutions.Nevertheless,Machine Learning(ML)techniques,which offer advanced regression tools to address complicated engineering issues,have been developed and widely explored.This study investigates the selected ML techniques to evaluate their suitability for application in the hot deformation behavior of metallic materials.The ML-based regression methods of Artificial Neural Networks(ANNs),Support Vector Machine(SVM),Decision Tree Regression(DTR),and Gaussian Process Regression(GPR)are applied to mathematically describe hot flow stress curve datasets acquired experimentally for a medium-carbon steel.Although the GPR method has not been used for such a regression task before,the results showed that its performance is the most favorable and practically unrivaled;neither the ANN method nor the other studied ML techniques provide such precise results of the solved regression analysis.
基金Shenzhen Science and Technology Program(KJZD20230923113900001)Project of Industry and Information Technology Bureau of Shenzhen Municipality(201806071403422960)。
文摘The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion at 1150℃(A3).The results show that A2 sample,extruded at 1100℃ with uniform γ+γ′duplex microstructures,demonstrates excellent hot deformation behavior at both 1050 and 1100℃.The true stress-true strain curves of A2 sample maintain a hardening-softening equilibrium over a larger strain range,with post-deformation average grain size of 5μm.The as-HIPed A1 sample and 1150℃ extruded A3 sample exhibit a softening region in deformation curves at 1050℃,and the grain microstructures reflect an incomplete recrystallized state,i.e.combination of fine recrystallized grains and initial larger grains,characterized by a necklace-like microstructure.The predominant recrystallization mechanism for these samples is strain-induced boundary migration.At 1150℃ with a strain rate of 0.001 s^(-1),the influence of the initial microstructure on hot deformation behavior and resultant microstructure is relatively less pronounced,and postdeformation microstructures are fully recrystallized grains.Fine-grained microstructures are conducive to maximizing the hot deformation potential of alloy.By judiciously adjusting deformation regimes,a fine and uniform deformed microstructure can be obtained.
文摘Using a Gleeble 3500 thermomechanical simulation testing machine,the hot deformation characteristics of 23Cr-8Ni steel were investigated under the conditions of 1000–1250℃ and 0.001‒10 s^(−1).Furthermore,the microstructure of the characterization region was analyzed to investigate the recrystallization behavior of 23Cr-8Ni steel.Results show that as the strain rate decreases and the deformation temperature increases,the flow stress decreases.Because the softening phenomenon occurs after the peak stress,the flow stress decreases.The stress index(n)is 4.28,and the thermal deformation activation energy(Q)is 588878 J/mol.Processing map is established,and an optimal thermal processing range of 0.001–0.1 s^(−1) and 1000–1200℃ is achieved,therefore greatly promoting the yield rate.
基金supported by the fund of the National Natural Science Foundation of China(52275322,51875127)。
文摘The popular constitutive models used in the field of hot forming of magnesium alloys can be divided into phenomenological models,machine learning models,and internal state variables(ISV)models based on physical mechanisms.Currently,there is a lack of comparison and evaluation regarding the suitability of different types of models.In this study,Mg-Gd-Y-Zr alloy is taken as the research object.The hot deformation behavior of the alloy was studied systematically.Subsequently,Arrhenius model with strain compensation,artificial neural network(ANN)model,and ISV model involving dynamic recrystallization(DRX),dislocation density and grain size evolution were established.ANN model demonstrates a higher level of accuracy in fitting the original stress-strain curves compared to both ISV model and modified Arrhenius model,but ANN model is not suitable for predicting the experimental results outside of the initial database.ISV model considers the impact of microstructure evolution history on stress,making it highly effective in reflecting the mechanical responses under complex loading condition.The established ISV model is embedded in the ABAQUS software,which shows good ability in calculating the mechanical response,dimension,and microstructure evolution information of the component during hot forming.
基金support was received from National Key Research and Development Plan from China:Demonstration and application of special steel for typical components of high-end equipment(2017YFB0703004).
文摘As high-speed railway transportation advances toward increased velocities,it is imperative to enhance the mechanical performance of EA4T axle steel,especially through microstructures regulation by thermal–mechanical processing.However,little research has been conducted on the phase transformation and microstructure evolution mechanism of EA4T steel under thermal–mechanical load,resulting in a lack of theoretical guidance.The hot deformation behavior and phase transformation mechanism of EA4T steel were investigated under different conditions of strain rates(0.01–10 s^(−1))and temperatures(850–1200℃).A relation of deformation stresses with Zener–Hollomon parameter was established to characterize the mechanical response and dynamic softening effect of EA4T steel during hot compression.The evolution of grain boundaries with different misorientations has been analyzed to evaluate the influence of strain rates and temperatures on the dynamic recrystallization.It was found that the grain refinement mechanisms of EA4T steel by dynamic recrystallization including twin-assisted boundary bulging,sub-grain rotation,and sub-grain growth.Transmission electron microscopy observations confirmed that dynamic recrystallization nuclei and small recrystallized grains impeded martensite phase nucleation during hot deformation,while the ongoing dynamic recrystallization consumed deformation stored energy and reduced dislocation density,which mitigated the stress concentration in the parent phase of martensite,thereby facilitating the uniform growth of martensite lath with a mixing structure of nanotwins and dislocations during quenching.
基金supported by the National Natural Science Foundation of China(nos.52201119,52371108)Frontier Exploration Project of Longmen Laboratory,China(no.LMQYTSKT014)The Joint Fund of Henan Science and Technology R&D Plan of China(no.242103810056).
文摘The hot deformation behavior of magnesium(Mg)alloys is significantly governed by the multi-physics coupling effects of temperature(T),strain rate(ε)and strain(ε),resulting in flow behavior that exhibits pronounced nonlinearity and multi-scale complexity.This study systematically investigates the hot deformation behavior of Mg-Y-Nd-(Sm)-Zr alloys.Sm alloying promotes recrystallization.The flow stress of Sm-containing alloys declines sharply towards a steady state after reaching its peak value.To overcome the limitations of the Arrhenius-type constitutive(AC)model in predicting complex nonlinear flow behavior,the AC and data hybrid informed neural network(ACINN)model is developed.This approach enhances the predictive accuracy and extends the applicability of the traditional AC model.The evolution of microstructure and recrystallization behavior under hot deformation conditions are investigated based on results from electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).The relationship between the power dissipation factor(η)and recrystallization behavior is further examined using K-means clustering analysis.The results demonstrate that dynamic recrystallization(DRX)behavior varies with theηvalue,comprising four distinct regimes:dynamic recovery(DRV),discontinuous dynamic recrystallization(DDRX)dominance,continuous dynamic recrystallization(CDRX)dominance and complete dynamic recrystallization.This analysis presents a new perspective for studying the hot deformation processes of Mg alloys.
基金Project supported by the Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation CenterProject(2013JSJJ0001)supported by the Teachers’Research Foundation of Central South UniversityChina
文摘The hot deformation behavior and microstructure evolution of 1460 Al-Li alloy were investigated by isothermal compression test conducted at various strain rates（10-3-10 s-1） and temperatures（573-773 K）. The flow stress curves were corrected by considering the friction at the platen/specimen interface and the temperature change due to the deformation heating. The effects of strain, strain rate and temperature on the deformation behavior were characterized by the Zener-Hollomon parameter in a hyperbolic-sine equation, and the constitutive equations were established according to the peak flow stress associated with dynamic recovery, dynamic recrystallization and the dissolution of T1 phases. In the entire strain rate and temperature range, the prediction capabilities of the developed constitutive equation are proved to be feasible and effective with a linear correlation coefficient and an average absolute relative error coefficient of 0.9909 and 6.72%, respectively.
基金Project(51301209) supported by the National Natural Science Foundation of China
文摘The hot deformation behavior of AA2014forging aluminum alloy was investigated by isothermal compression tests attemperatures of350-480°C and strain rates of0.001-1s-1on a Gleeble-3180simulator.The corresponding microstructures of thealloys under different deformation conditions were studied using optical microscopy(OM),electron back scattered diffraction(EBSD)and transmission electron microscopy(TEM).The processing maps were constructed with strains of0.1,0.3,0.5and0.7.The results showed that the instability domain was more inclined to occur at strain rates higher than0.1s-1and manifested in theform of local non-uniform deformation.At the strain of0.7,the processing map showed two stability domains:domain I(350-430°C,0.005-0.1s-1)and domain II(450-480°C,0.001-0.05s-1).The predominant softening mechanisms in both of the twodomains were dynamic recovery.Uniform microstructures were obtained in domain I,and an extended recovery occurred in domainII,which would lead to the potential sub-grain boundaries progressively transforming into new high-angle grain boundaries.Theoptimum hot working parameters for the AA2014forging aluminum alloy were determined to be370-420°C and0.008-0.08s-1.
基金supported by the National Key R&D Program of China(No.2021YFB3701100)the National Natural Science Foundation of China(No.52271091)the China Scholarship Council(No.202206050135)。
文摘The hot compression behavior of as-extruded Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy was studied on a Gleeble-3500 thermal simulation machine.Experiments were conducted at temperatures ranging from 523 to 673 K and strain rates ranging from 0.001 to 1 s^(-1).Results showed that an increase in the strain rate or a decrease in deformation temperature led to an increase in true stress.The constitutive equation and processing maps of the alloy were obtained and analyzed.The influence of deformation temperatures and strain rates on microstructural evolution and texture was studied with the assistance of electron backscatter diffraction(EBSD).The as-extruded alloy exhibited a bimodal structure that consisted of deformed coarse grains and fine equiaxed recrystallized structures(approximately 1.57μm).The EBSD results of deformed alloy samples revealed that the recrystallization degree and average grain size increased as the deformation temperature increased.By contrast,dislocation density and texture intensity decreased.Compressive texture weakened with the increase in the deformation temperature at the strain rate of 0.01 s-1.Most grains with{0001}planes tilted away from the compression direction(CD)gradually.In addition,when the strain rate decreased,the recrystallization degree and average grain size increased.Meanwhile,the dislocation density decreased.Texture appeared to be insensitive to the strain rate.These findings provide valuable insights into the hot compression behavior,microstructural evolution,and texture changes in the Mg-0.6Mn-0.5Al-0.5Zn-0.4Ca alloy,contributing to the understanding of its processing-microstructure-property relationships.
基金financially supported by the National Natural Science Foundation of China(No.51101052)the National Science Foundation(No.IRES 1358088)
文摘Hot deformation behavior of the Cu-Cr-Zr alloy was investigated using hot compressive tests in the tem- perature range of 650-850℃ and strain rate range of 0.001-10 s-1. The constitutive equation of the alloy based on the hyperbolic-sine equation was established to characterize the flow stress as a function of strain rate and deformation temperature. The critical conditions for the occurrence of dynamic recrystallization were determined based on the alloy strain hardening rate curves. Based on the dynamic material model, the processing maps at the strains of 0.3, 0.4 and 0.5 were obtained. When the true strain was 0.5, greater power dissipation efficiency was observed at 800-850 ℃ and under 0.001-0.1 s-1, with the peak efficiency of 47%. The evolution of DRX microstructure strongly depends on the deformation temperature and the strain rate. Based on the processing maps and microstructure evolution, the optimal hot working conditions for the Cu-Cr-Zr alloy are in the temperature range of 800-850 ℃ and the strain rate range of 0.001-0.1 s-1.
基金Project(2013HH100055) supported by the Basic Research and Science and Technology Innovation Fund of Foshan City,China
文摘Hot compression tests in the temperature range of 340-450 ℃ and strain rate range of 0.001-1 s^-1 of spray-formed 7055 aluminum alloy were carried out to study its hot deformation behavior. Three phenomenological models including Johnson-Cook, modified Fields-Backofen and Arrhenius-type were introduced to predict the flow stresses during the compression process. And then, a comparative predictability of the phenomenological models was estimated in terms of the relative errors, correlation coefficient（R）, and average absolute relative error（AARE）. The results indicate that Johnson-Cook model and modified Fields-Backofen model cannot well predict the hot deformation behavior due to the large deviation in the process of line regression fitting. Arrhenius-type model obtains the best fit through combining the effect of strain rate and temperature.
基金Project(51135007)supported by the National Natural Science Foundation of ChinaProject(IRT13087)supported by the Innovative Research Team Development Program of Ministry of Education of China+1 种基金Project(2012-86)supported by the High-end Talent Leading Program of Hubei Province,ChinaProject(2012-P08)supported by State Key Laboratory of Materials Processing and Die&Mould Technology,China
文摘Q345E as one of typical low alloy steels is widely used in manufacturing basic components in many fields because of its eminent formability under elevated temperature. In this work, the deformation behavior of Q345E steel was investigated by hot compression experiments on Gleeble-3500 thermo-mechanical simulator with the temperature ranging from 850 ℃ to 1150 ℃ and strain rate ranging from 0.01 s-1 to 10 s-1. The experimental results indicate that dynamic softening of Q345E benefits from increasing deformation temperature and decreasing strain rate. The mathematical relationship between dynamic softening degree and deformation conditions is established to predict the dynamic softening degree quantitatively, which is further proved by some optical microstructures of Q345E. In addition, the experimental results also reveal that the stress level decreases with increasing deformation temperature and decreasing strain rate. The constitutive equation for flow stress of Q345E is formulated by Arrihenius equation and the modified Zener-Hollomon parameter considering the compensation of both strain and strain rate. The flow stress values predicted by the constitutive equation agree well with the experimental values, realizing the accurate prediction of the flow stress of Q345E steel under hot deformation.
基金financially supported by the National Natural Science Foundation of China(No.51175431)
文摘The hot deformation behavior of Ti22A125 Nb was investigated by hot compression test.The flow stressstrain curves can be divided into two types：conventional dynamic recrystallization（DRX） and discontinuous DRX.The different softening mechanism and micro structure observation of conventional DRX and discontinuous DRX were analyzed.The processing map（PM） of Ti22A125 Nb was built to predict the safe deformation region.The optimal low strain rate domain（DOM I） with high power dissipation efficiency indicates the complete DRX.Additionally,in the high strain rate and low-temperature domain（DOM Ⅲ）,the power dissipation efficiency is low and some adiabatic shear bands and glide bands are observed,which are unsafe and should be avoided.Finally,the DRX map was established.In DOM I,it reveals low dislocation density and high DRX content,which is in agreement with PM.
基金financially supported from the Southwest Aluminum(group)Co,.Ltd under the Project(No.JZKG20190099)。
文摘Hot deformation behavior and microstructural evolution of as-homogenized 7A65 Al alloy under isothermal compression at temperatures of 573-713 K and strain rates of 0.1-10.0 s-1were investigated.It was found that the flow stress of 7A65 Al alloy exhibited a typical dynamic recovery characteristic at high-temperature deformation conditions,and a sixth-order polynomial strain compensated Arrhenius constitutive equation was proposed to describe the flow behavior.Based on the dynamic material model and the Prasad standard,the hot processing map was established.The optimal processing conditions were within the temperature range of 633-713 K and the strain rate range of 0.1-0.5 s^(-1)when the true strain exceeded 0.6.Deformation temperature and strain rate had an obvious effect on the micros tructure evolution of 7A65Al alloy,and the deformed microstructures were mainly composed of deformed grains and recovery structure.The main softening mechanism was dynamic recovery at the temperature of 573-713 K and the strain rate of 0.1-10.0s-1,but dynamic recrystallization was enhanced with the increase in temperature.
基金Item Sponsored by National Science and Technology Support Plan of China(2007BAE51B02)
文摘The hot deformation behavior of S31042 austenitic heat-resistant steel was investigated over the tempera- ture range of 900--1 200 ℃ and strain rate range of 0.01--10 s- 1 using hot compression tests and the corresponding flow curves were obtained. The hot deformation activation energy of the test steel is 625 kJ/mol. The hot deformation equation and the relationship between the peak stresses, deformation temperature and strain rate were set up. The Zener-Hollomon parameter under various conditions was determined. The relation between the Zener-Hollomon parameter and the microstructure evolution of test steel was discussed. With the decrease of Zener-Hollomon param- eter, the microstructure of test steel transforms from deformation instability to dynamic recovery, partial dynamic recrystallization, full dynamic recrystallization with equiaxial structure, and finally to full dynamic recrystaUization with mixed crystal structure. The deformation condition can be adjusted easily by utilizing the Zener-Hollomon pa- rameter to obtain equiaxial microstructure.
基金supported by the Foundation for Science and Technology Development Project of Shandong (No.2014GGX102006)
文摘The isothermally compression deformation behavior of an elevated Cu/Li weight ratio Al–Cu–Li alloy was investigated under various deformation conditions.The isothermal compression tests were carried out in a temperature range from 300 to 500℃ and at a strain rate range from 0.001 to 10 s^-1.The results show that the peak stress level decreases with temperature increasing and strain rate decreasing,which is represented by the Zener–Hollomon parameter Z in the hyperbolic sine equation with the hot deformation activation energy of 218.5 k J/mol.At low Z value,the dynamic recrystallized grain is well formed with clean high-angle boundaries.At high Z value,a high dislocation density with poorly developed cellularity and considerable fine dynamic precipitates are observed.Based on the experimental data and dynamic material model,the processing maps at strain of 0.3,0.5 and 0.7 were developed to demonstrate the hot workability of the alloy.The results show that the main softening mechanism at high Z value is precipitate coarsening and dynamic recovery;the dynamic recrystallization of the alloy can be easily observed as ln Z ≤ 29.44,with peak efficiency of power dissipation of around 70%.At strains of 0.3,0.5 and 0.7,the flow instability domains are found at higher strain rates,which mainly locate at the upper part of processing maps.In addition,when the strain rate is 0.001 or 0.02 s^-1,there is a particular instability domain at 300–350℃.
基金supported by the Qinghai Provincial Science and Technology Program (No.2020-ZJ-707)the Financial supports from the Natural Science Foundation of China (No.52261016).
文摘Graphene nanoplates(GNPs)-reinforced magnesium matrix composites have been attracted great attention.However,knowledge is lack for the hot deformation behavior of GNP-reinforced magnesium(GNPs/Mg)composite.In this study,the fine-grained GNPs/Mg composite was fabricated by powder metallurgy process followed by extrusion.The hot deformation behavior,microstructure evolution and dynamic recrystallization(DRX)mechanism of fine-grained GNPs/Mg composite were investigated by hot compression test and electron back-scatter diffraction(EBSD).The hot compression tests of the composite were conducted at temperatures between 423 and 573 K with the strain rates from 0.001 to 1 s^(-1).The strain compensated power law equation was established to describe the hot deformation behavior of the composites.The stress exponent and activation energy of the composite are 7.76 and 83.23 kJ/mol,respectively,suggesting that the deformation mechanism is grain boundary slip controlled dislocation climb creep.The abnormally high stress exponent and activation energy are unattainable in the composite due to the fine grain size of the composites and the absence of Zener pinning and Orowan effects of GNPs reinforcement.The grain size increases with the decrease in Zener-Hollomn(Z)parameter,which can be well fitted by power-law relationship.With the increase in grain size and decrease in Z parameter,the geometrically necessary dislocation density decreases,which shows the approximately power-law relationship.A random and weak texture was formed after hot compression.The discontinuous dynamic recrystallization and continuous dynamic recrystallization mechanism dominated the DRX behavior at 473 K/0.001 s^(-1) and 573 K/0.001 s^(-1),respectively.
基金the National Natural Science Foundation of China(Grant No.51464035).
文摘The isothermal compression test for Ti-6Al-7Nb alloy was conducted by using Gleeble-3800 thermal simulator.The hot deformation behavior of Ti-6Al-7Nb alloy was investigated in the deformation temperature ranges of 940-1030℃and the strain rate ranges of 0.001-10 s^(-1).Meanwhile,the activation energy of thermal deformation was computed.The results show that the flow stress of Ti-6Al-7Nb alloy increases with increasing the strain rate and decreasing the deformation temperature.The activation energy of thermal deformation for Ti-6Al-7Nb alloy is much greater than that for self-diffusion ofα-Ti andβ-Ti.Considering the influence of strain on flow stress,the strain-compensated Arrhenius constitutive model of Ti-6Al-7Nb alloy was established.The error analysis shows that the model has higher accuracy,and the correlation coefficient r and average absolute relative error are 0.9879 and 4.11%,respectively.The processing map(PM)of Ti-6Al-7Nb alloy was constructed by the dynamic materials model and Prasad instability criterion.According to PM and microstructural observation,it is found that the main form of instability zone is local flow,and the deformation mechanisms of the stable zone are mainly superplasticity and dynamic recrystallization.The optimal processing parameters of Ti-6Al-7Nb alloy are determined as follows:960-995℃/0.01-0.18 s^(-1)and 1000-1030℃/0.001-0.01 s^(-1).
基金supported by the National Natural Science Foundation of China(No.50671028)
文摘The true stress-true strain curves of Ti-6Al-2Zr-IMO-IV alloy with hydrogen were obtained by hot compression test. The microstructures of the alloy before and after thermo-compression were observed. The apparent activation energies of deformation were calculated for the alloy with and without hydrogen. The behavior and mechanism of deformation for hydrogenated Ti-6A1-2Zr-IMO-IV alloy at high temperature were analyzed. The relationship between hydrogenation time and hydrogen content at 800 ℃ can be expressed as the equation： CH（t）=1.2-1.2exp（-t/120）. The true stress-true strain curves of hot compression for Ti-6Al-2Zr-IMO-IV alloy with hydrogen first move down and then move up as hydrogen content increases. Appropriate hydrogen content can reduce the peak of flow stress to minimal value. The apparent activation energies of deformation of the alloy with 0.47% hydrogen content and without hydrogen were calculated as 140 kJ·mol^-1 and 390 kJ-mol^-1, respectively, at 800 ℃ and at strain rate 8.3×10^4 s^-1. The apparent activation energy of deformation increases when the strain rate enhances from 8.3×10^-4 s^-1 to 8.3×10^-2 s^-1.
基金supported by the National Key R&D Program of China(Nos.2021YFB3700601 and 2019YFA0705304)the IMR Innovation Fund(No.2023-PY08).
文摘The hot deformation behavior of a newly developed Ni–W–Cr superalloy for use in 800℃molten salt reactors(MSRs)was looked into by isothermal compression tests in the temperature range of 1050–1200℃with a strain rate of 0.001–1 s^(−1)under a true strain of 0.693.An Arrhenius-type model for the Ni–W–Cr superalloy was constructed by fitting the corrected flow stress data.In this model,the effect of dispersion of solid solution elements during thermal deformation on microstructure evolution was considered,as well as the effects of friction and adiabatic heating on the temperature and strain rate-dependent variation of flow stresses.The hot deformation activation energy of the Ni–W–Cr superalloy was 323 kJ/mol,which was less than that of the Hastelloy N alloy(currently used in MSRs).According to the rectified flow stress data,processing maps were created.In conjunction with the corresponding deformation microstructures,the flow instability domains of the Ni–W–Cr superalloy were determined to be 1050–1160℃/0.03–1 s^(−1)and 1170–1200℃/0.001–0.09 s^(−1).In these deformation conditions,a locally inhomogeneous microstructure was caused by flow-i.e.,incomplete dynamic recrystallization and hot working parameters should avoid sliding into these domains.The ideal processing hot deformation domain for the Ni–W–Cr superalloy was determined to be 1170–1200℃/0.6–1 s^(−1).
