In order to study the effect of dynamic recrystallization on the metal flow behavior during thermal deformation,the elevated temperature compression experiments of CuCrZr alloy and 35CrMo steel are carried out using G...In order to study the effect of dynamic recrystallization on the metal flow behavior during thermal deformation,the elevated temperature compression experiments of CuCrZr alloy and 35CrMo steel are carried out using Gleeble-3810 thermal simulator.It is proved that the samples underwent obvious dynamic recrystallization behavior during thermal deformation by microstructure observation of deformed specimens.The size of recrystallized grains increases as the temperature improved and the strain rate decreased.Meanwhile,the net softening rate caused by dynamic recrystallization is determined based on the stress-dislocation relationship.It can be found that the value of net softening rate increases quadratically as the Z parameter decreases,and the dynamic recrystallization net softening rate of CuCrZr alloy and 35CrMo steel are calculated to be 21.9%and 29.8%,respectively.Based on the dynamic recrystallization softening effect proposed,the novel elevated temperature flow constitutive models of two different alloys are proposed,and the related parameters are well defined and solved in detail.The predicted values of the obtained models are agreed well with the experimental values.展开更多
The dynamic recrystallization(DRX) process of hot compressed aluminium alloy 7050 was predicted using cellular automaton(CA) combined with topology deformation. The hot deformatation characteristics of aluminium alloy...The dynamic recrystallization(DRX) process of hot compressed aluminium alloy 7050 was predicted using cellular automaton(CA) combined with topology deformation. The hot deformatation characteristics of aluminium alloy 7050 were investigated by hot uniaxial compression tests in order to obtain the material parameters used in the CA model. The influences of process parameters(strain, strain rate and temperature) on the fraction of DRX and the average recrystallization grain(R-grain) size were investigated and discussed. It is found that larger stain, higher temperature and lower strain rate(less than 0.1 s^(–1)) are beneficial to the increasing fraction of DRX. And the deformation temperature affects the mean R-grain size much more greatly than other parameters. It is also noted that there is a critical strain for the occurrence of DRX which is related to strain rate and temperature. In addition, it is shown that the CA model with topology deformation is able to simulate the microstructural evolution and the flow behavior of aluminium alloy 7050 material under various deformation conditions.展开更多
The prediction of microstructure evolution plays an important role in the design of forging process. In the present work, the cellular automaton (CA) program was developed to simulate the process of dynamic recrystall...The prediction of microstructure evolution plays an important role in the design of forging process. In the present work, the cellular automaton (CA) program was developed to simulate the process of dynamic recrystallization (DRX) for aluminium alloy 7050. The material constants in CA models, including dislocation density, nucleation rate and grain growth, were determined by the isothermal compress tests on Gleeble 1500 machine. The model of dislocation density was obtained by linear regression method based on the experimental results. The influences of the deformation parameters on the percentage of DRX and the mean grain size for aluminium alloy 7050 were investigated in details by means of CA simulation. The simulation results show that, as temperature increases from 350 to 450 ℃ at a strain rate of 0.01 s?1, the percentage of DRX also increases greatly and the mean grain size decreases from 50 to 39.3 μm. The mean size of the recrystallied grains (R-grains) mainly depends on the Zener-Hollomon parameter. To obtain fine grain, the desired deformation temperature is determined from 400 to 450 ℃.展开更多
The dynamic recrystallization behavior of high strength steel during hot deformation was investigated.The hot compression test was conducted in the temperature range of 950-1150 °C under strain rates of 0.1,1 and...The dynamic recrystallization behavior of high strength steel during hot deformation was investigated.The hot compression test was conducted in the temperature range of 950-1150 °C under strain rates of 0.1,1 and 5 s-1.It is observed that dynamic recrystallization(DRX) is the main flow softening mechanism and the flow stress increases with decreasing temperature and increasing strain rate.The relationship between material constants(Q,n,α and ln A) and strain is identified by the sixth order polynomial fit.The constitutive model is developed to predict the flow stress of the material incorporating the strain softening effect and verified.Moreover,the critical characteristics of DRX are extracted from the stress-strain curves under different deformation conditions by linear regression.The dynamic recrystallization volume fraction decreases with increasing strain rate at a constant temperature or decreasing deformation temperature under a constant strain rate.The kinetics of DRX increases with increasing deformation temperature or strain rate.展开更多
The hot deformation behaviors of Cr5 steel were investigated.The hot compression tests were conducted in the temperature range of 900-1150 °C under strain rates of 0.01,0.1 and 1 s^(-1).The constitutive equation ...The hot deformation behaviors of Cr5 steel were investigated.The hot compression tests were conducted in the temperature range of 900-1150 °C under strain rates of 0.01,0.1 and 1 s^(-1).The constitutive equation and material constants(Q,n,α ln A) are obtained according to the hyperbolic sine function and Zener-Hollomon parameter.Besides,dynamic recrystallization(DRX) grain size model and critical strain model are acquired.The processing maps with the strain of 0.1,0.3 and 0.5 are obtained on the basis of dynamic materials model.It has been observed that DRX occurs at high temperature and low strain rate.According to the processing map,the safety region exists in the temperature range of 920-1150 °C with strain rate of 0.01-0.20 s^(-1).展开更多
A modified cellular automaton(CA) program was developed to simulate the process of dynamic recrystallization(DRX) for 23Co13Ni11Cr3Mo ultrahigh strength steel.In this model,influences of deformation parameters on hard...A modified cellular automaton(CA) program was developed to simulate the process of dynamic recrystallization(DRX) for 23Co13Ni11Cr3Mo ultrahigh strength steel.In this model,influences of deformation parameters on hardening rate and solute drag effect were considered.Moreover,an inverse analysis method was proposed for parameters identification of dislocation model and solute drag effect based on the results of isothermal compression tests on Gleeble-1500.Then,simulated microstructures under different deformation conditions were compared with those of experiments.A good agreement is achieved.Furthermore,influences of deformation parameters on microstructure evolution for 23Co13Ni11Cr3Mo steel were investigated in details.High strain is an effective measure to refine grain and improve homogeneity.Meanwhile,the desired deformation parameters are temperature of 1000-1050 °C and strain rate of 0.008-0.01 s-1 for obtaining grains smaller than 22.5 μm.展开更多
Using the Gleeble-1500 D simulator, the hot deformation behavior and dynamic recrystallization critical conditions of the 10%Ti C/Cu-Al2O3(volume fraction) composite were investigated by compression tests at the tempe...Using the Gleeble-1500 D simulator, the hot deformation behavior and dynamic recrystallization critical conditions of the 10%Ti C/Cu-Al2O3(volume fraction) composite were investigated by compression tests at the temperatures from 450 °C to 850 °C with the strain rates from 0.001 s-1 to 1 s-1. The results show that the softening mechanism of the dynamic recrystallization is a feature of high-temperature flow true stress-strain curves of the composite, and the peak stress increases with the decreasing deformation temperature or the increasing strain rate. The thermal deformation activation energy was calculated as 170.732 k J/mol and the constitutive equation was established. The inflection point in the lnθ-ε curve appears and the minimum value of-(lnθ)/ε-ε curve is presented when the critical state is attained for this composite. The critical strain increases with the increasing strain rate or the decreasing deformation temperature. There is linear relationship between critical strain and peak strain, i.e., εc=0.572εp. The predicting model of critical strain is described by the function of εc=1.062×10-2Z0.0826.展开更多
High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material...High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material cost poses substantial challenges for optimizing thermal processing parameters through repetitive experimental trials.In this work,hot compression experiments on high-purity silver were conducted using a Gleeble-3800 thermal simulator.The high temperature deformation behaviors,dynamic recovery(DRV)and dynamic recrystallization(DRX)of high-purity silver were studied by constructing an Arrhenius constitutive equation and developing thermal processing maps.The results show that plastic instability of high-purity silver occurs at high strain rates and the optimized hot processing parameters are the strain rate below 0.001 s^(−1) and the temperature of 340−400℃.Microstructural observations exhibit that DRV prefers to occur at lower deformation temperatures(e.g.,250℃).This is attributed to the low stacking fault energy of high-purity silver,which facilitates the decomposition of dislocations into partial dislocations and promotes high-density dislocation accumulation.Furthermore,DRX in high-purity silver becomes increasingly pronounced with increasing deformation temperature and reaches saturation at 350℃.展开更多
The microstructure evolution of 7A85 aluminum alloy at the conditions of strain rate(0.001−1 s^(−1))and deformation temperature(250−450°C)was studied by optical microscopy(OM)and electron back scattering diffract...The microstructure evolution of 7A85 aluminum alloy at the conditions of strain rate(0.001−1 s^(−1))and deformation temperature(250−450°C)was studied by optical microscopy(OM)and electron back scattering diffraction(EBSD).Based on the K-M dislocation density model,a two-stage K-M dislocation density model of 7A85 aluminum alloy was established.The results reveal that dynamic recovery(DRV)and dynamic recrystallization(DRX)are the main mechanisms of microstructure evolution during thermal deformation of 7A85 aluminum alloy.350−400°C is the transformation zone from dynamic recovery to dynamic recrystallization.At low temperature(≤350°C),DRV is the main mechanism,while DRX mostly occurs at high temperature(≥400°C).At this point,the sensitivity of microstructure evolution to temperature is relatively high.As the temperature increased,the average misorientation angle(θˉ_(c))increased significantly,ranging from 0.93°to 7.13°.Meanwhile,the f_(LAGBs) decreased with the highest decrease of 24%.展开更多
The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1...The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1. The activation energy（Q） for the tested steel is calculated to be around 682.99 k J/mol at a deformation strain of 0.6. Microstructural analysis by SEM shows that the dynamic recrystallization（DRX） behavior is dependent sensitively on the deformation strain, temperature and strain rate, while an exponential relationship between DRX grain size and Z parameter is obtained from the computational formula. Moreover, the M6C-type carbides（〈1 μm） act as the main prohibitor of grain coarsening, and the polynomial regression relationship between them is worked out. With electron backscatter diffraction（EBSD） observation, DRX is the main nucleation mechanism responsible for the formation of new grains during hot compression. In conclusion, the interaction between DRX affected by hot deformation parameters and carbides precipitation determines the ultimate grain size refinement.展开更多
The hot deformation behavior of Al-6.2Zn-0.70Mg-0.30Mn-0.17 Zr alloy and its microstructural evolution were investigated by isothermal compression test in the deformation temperature range between 623 and 773 K and th...The hot deformation behavior of Al-6.2Zn-0.70Mg-0.30Mn-0.17 Zr alloy and its microstructural evolution were investigated by isothermal compression test in the deformation temperature range between 623 and 773 K and the strain rate range between 0.01 and 20 s^(-1).The results show that the flow stress decreased with decreasing strain rate and increasing deformation temperature.At low deformation temperature(≤673 K) and high strain rate(≥1 s^(-1)),the main flow softening was caused by dynamic recovery;conversely,at higher deformation temperature and lower strain rate,the main flow softening was caused by dynamic recrystallization.Moreover,the slipping mechanism transformed from dislocation glide to grain boundary sliding with increasing the deformation temperature and decreasing the strain rate.According to TEM observation,numerous Al_3Zr particles precipitated in matrix,which could effectively inhibit the dynamic recrystallization of the alloy.Based on the processing map,the optimum processing conditions for experimental alloy were in deformation temperature range from 730 K to 773 K and strain rate range from 0.033 s^(-1) to 0.18 s^(-1) with the maximum efficiency of 39%.展开更多
In order to present the microstructures of dynamic recrystallization(DRX) in different deformation zones of hot extruded NiTi shape memory alloy(SMA) pipe coupling,a simulation approach combining finite element method...In order to present the microstructures of dynamic recrystallization(DRX) in different deformation zones of hot extruded NiTi shape memory alloy(SMA) pipe coupling,a simulation approach combining finite element method(FEM) with cellular automaton(CA) was developed and the relationship between the macroscopic field variables and the microscopic internal variables was established.The results show that there exists a great distinction among the microstructures in different zones of pipe coupling because deformation histories of these regions are diverse.Large plastic deformation may result in fine recrystallized grains,whereas the recrystallized grains may grow very substantially if there is a rigid translation during the deformation,even if the final plastic strain is very large.As a consequence,the deformation history has a significant influence on the evolution path of the DRX as well as the final microstructures of the DRX,including the morphology,the mean grain size and the recrystallization fraction.展开更多
ZK60-xcerium alloys were studied,where x mass fraction is 0, 0.52%, 0.94%, 1.51% and 1.98%, respectively. Influence of Ce contents and heat-treatment on microstructure and tensile properties was analyzed. The results ...ZK60-xcerium alloys were studied,where x mass fraction is 0, 0.52%, 0.94%, 1.51% and 1.98%, respectively. Influence of Ce contents and heat-treatment on microstructure and tensile properties was analyzed. The results show that cast ZK60 alloy containing no Ce has coarse crystal grains, and lots of segregation aggregates around the grain-boundary. However, the alloys containing Ce have refined grains, and grain-boundaries are purified at the same time. Obvious dynamic recrystallization occurs in tested alloys after hot-extrusion. Tensile strength heightens with the increase of Ce content, and grows higher after aging at 150℃ for 024 h （T5 treatment）. Comparing tensile properties of investigated alloys in different states, it can be concluded that synthetical properties of the alloy with 1.51% Ce addition is the best of all. In extruded state, σb and δ of this alloy are 318.6 MPa and 14.4%, respectively. After aging for 24 h ,σb is 338.6 MPa and δ is 15.6%.展开更多
Single hit compression tests were performed at 1 223-1 473 K and strain rate of 0.1-10 s-1 to study hot deformation behavior and flow stress model of F40MnV steel. The dependence of the peak stress, initial stress, sa...Single hit compression tests were performed at 1 223-1 473 K and strain rate of 0.1-10 s-1 to study hot deformation behavior and flow stress model of F40MnV steel. The dependence of the peak stress, initial stress, saturation stress, steady state stress and peak stain on Zener-Hollomon parameter were obtained. The mathematical models of dynamic recrystallization fraction and grain size were also obtained. Based on the tested data, the flow stress model of F40MnV steel was established in dynamic recovery region and dynamic recrystallization region, respectively. The results show that the activation energy for dynamic recrystallization is 278.6 kJ/mol by regression analysis. The flow stress model of F40MnV steel is proved to approximate the tested data and suitable for numerical simulation of hot forging.展开更多
The hot-compression of Al-IMn-IMg （mass fraction, %） alloy sample was carried out on a Gleeble-1500 thermo-simulator at deformation temperatures from 320 to 400 ℃ and strain rates from 0.1 to 10 s 1 by total strain...The hot-compression of Al-IMn-IMg （mass fraction, %） alloy sample was carried out on a Gleeble-1500 thermo-simulator at deformation temperatures from 320 to 400 ℃ and strain rates from 0.1 to 10 s 1 by total strain of 1.4. Microstructure and texture evolution of the hot-compressed alloy were investigated by optical microscopy and X-ray diffraction analysis, respectively. The results show that the relationship among flow stress a, deformation temperature T and strain rate ε can be expressed in the form of βσ = lnε＋Q/（RT）-lnA. The threshold value of In Z （Z is Zener-Hollomon parameter） characterizing the dynamic recrystallization （DRX） is 46, below which the DRX takes place. A strong P orientation {011}（455） associated with a weak cube orientation { 100} （001） is found in the recrystallized sample during hot-compression.展开更多
The hot deformation simulation of a ZK60 magnesiuln alloy at different temperatures from 373 to 673 K and different strain rates of 0.1, 0.01 and 0.002 s^-1 was studied by using the Gleebe-1500 simulator. The plastic ...The hot deformation simulation of a ZK60 magnesiuln alloy at different temperatures from 373 to 673 K and different strain rates of 0.1, 0.01 and 0.002 s^-1 was studied by using the Gleebe-1500 simulator. The plastic deformation behavior was measured and the deformation activation energy was calculated. The microstructures of ZK60 magnesium alloy with an addition of neodymium during the deformation process were observed by using Polyvar-MET optical microscope and Tecnai G^2 20 TEM. The results show that the working hardening, the dynamic recovery and the dynamic recrystallization occur during the plastic deformation process at different temperatures and strain rates. The dynamic recrystallization starts when the temperature is over 473 K and the DRX grain size after hot deformation is only 5-10 μm. So the refined grains improve both the tensile strength and the elongation of alloys at room temperature. Neodymium is added into the alloy and a precipitate phase Mg12Nd that impedes the movement of dislocations is formed, which benefits to increasing mechanical properties of ZK60 magnesium alloy.展开更多
Microstructures and mechanical properties of （Mg-2.0%Ce-0.7%Zn-0.7%Zr） alloy were studied. The results of scanning electron microscopy show that Mg12Ce phase mainly distributes at the grain boundaries. The fine (Mg1...Microstructures and mechanical properties of （Mg-2.0%Ce-0.7%Zn-0.7%Zr） alloy were studied. The results of scanning electron microscopy show that Mg12Ce phase mainly distributes at the grain boundaries. The fine (Mg12Ce) phase can apparently elevate recrystallization temperature by preventing the grain boundary migration. No dynamic recrystallization occurs during the hot-extrusion. The mechanical properties of as extruded specimens are （σb=278.5 MPa,） δ=12.0%, while those of the specimens annealed at 250 ℃ for 100 h are σb=（272.6 MPa,） δ=（11.3%,） which indicate that the alloy has good mechanical properties at room temperature.展开更多
基金Project(2019zzts525)supported by the Fundamental Research Funds for the Central Universities,ChinaProjects(U1837207,U1637601)supported by the National Natural Science Foundation of China
文摘In order to study the effect of dynamic recrystallization on the metal flow behavior during thermal deformation,the elevated temperature compression experiments of CuCrZr alloy and 35CrMo steel are carried out using Gleeble-3810 thermal simulator.It is proved that the samples underwent obvious dynamic recrystallization behavior during thermal deformation by microstructure observation of deformed specimens.The size of recrystallized grains increases as the temperature improved and the strain rate decreased.Meanwhile,the net softening rate caused by dynamic recrystallization is determined based on the stress-dislocation relationship.It can be found that the value of net softening rate increases quadratically as the Z parameter decreases,and the dynamic recrystallization net softening rate of CuCrZr alloy and 35CrMo steel are calculated to be 21.9%and 29.8%,respectively.Based on the dynamic recrystallization softening effect proposed,the novel elevated temperature flow constitutive models of two different alloys are proposed,and the related parameters are well defined and solved in detail.The predicted values of the obtained models are agreed well with the experimental values.
基金Project(2012ZX04010-8)supported by National Key Technology R&D Program of China
文摘The dynamic recrystallization(DRX) process of hot compressed aluminium alloy 7050 was predicted using cellular automaton(CA) combined with topology deformation. The hot deformatation characteristics of aluminium alloy 7050 were investigated by hot uniaxial compression tests in order to obtain the material parameters used in the CA model. The influences of process parameters(strain, strain rate and temperature) on the fraction of DRX and the average recrystallization grain(R-grain) size were investigated and discussed. It is found that larger stain, higher temperature and lower strain rate(less than 0.1 s^(–1)) are beneficial to the increasing fraction of DRX. And the deformation temperature affects the mean R-grain size much more greatly than other parameters. It is also noted that there is a critical strain for the occurrence of DRX which is related to strain rate and temperature. In addition, it is shown that the CA model with topology deformation is able to simulate the microstructural evolution and the flow behavior of aluminium alloy 7050 material under various deformation conditions.
基金Project(2005CB724105) supported by the Major State Basic Research Program of ChinaProject(IRT0549) supported by Program for Changjiang Scholars and Innovative Research Team in University
文摘The prediction of microstructure evolution plays an important role in the design of forging process. In the present work, the cellular automaton (CA) program was developed to simulate the process of dynamic recrystallization (DRX) for aluminium alloy 7050. The material constants in CA models, including dislocation density, nucleation rate and grain growth, were determined by the isothermal compress tests on Gleeble 1500 machine. The model of dislocation density was obtained by linear regression method based on the experimental results. The influences of the deformation parameters on the percentage of DRX and the mean grain size for aluminium alloy 7050 were investigated in details by means of CA simulation. The simulation results show that, as temperature increases from 350 to 450 ℃ at a strain rate of 0.01 s?1, the percentage of DRX also increases greatly and the mean grain size decreases from 50 to 39.3 μm. The mean size of the recrystallied grains (R-grains) mainly depends on the Zener-Hollomon parameter. To obtain fine grain, the desired deformation temperature is determined from 400 to 450 ℃.
基金Project (51322405) supported by the National Natural Science Foundation of ChinaProject (CX2013B085) supported by Hunan Provincial Innovation Foundation for Postgraduate,China
文摘The dynamic recrystallization behavior of high strength steel during hot deformation was investigated.The hot compression test was conducted in the temperature range of 950-1150 °C under strain rates of 0.1,1 and 5 s-1.It is observed that dynamic recrystallization(DRX) is the main flow softening mechanism and the flow stress increases with decreasing temperature and increasing strain rate.The relationship between material constants(Q,n,α and ln A) and strain is identified by the sixth order polynomial fit.The constitutive model is developed to predict the flow stress of the material incorporating the strain softening effect and verified.Moreover,the critical characteristics of DRX are extracted from the stress-strain curves under different deformation conditions by linear regression.The dynamic recrystallization volume fraction decreases with increasing strain rate at a constant temperature or decreasing deformation temperature under a constant strain rate.The kinetics of DRX increases with increasing deformation temperature or strain rate.
基金Project(51322405)supported by the National Natural Science Foundation of China
文摘The hot deformation behaviors of Cr5 steel were investigated.The hot compression tests were conducted in the temperature range of 900-1150 °C under strain rates of 0.01,0.1 and 1 s^(-1).The constitutive equation and material constants(Q,n,α ln A) are obtained according to the hyperbolic sine function and Zener-Hollomon parameter.Besides,dynamic recrystallization(DRX) grain size model and critical strain model are acquired.The processing maps with the strain of 0.1,0.3 and 0.5 are obtained on the basis of dynamic materials model.It has been observed that DRX occurs at high temperature and low strain rate.According to the processing map,the safety region exists in the temperature range of 920-1150 °C with strain rate of 0.01-0.20 s^(-1).
基金Project(2011CB706802)supported by the National Basic Research Program of ChinaProject(2012ZX04010-081)supported by National Science and Technology Major Program of China
文摘A modified cellular automaton(CA) program was developed to simulate the process of dynamic recrystallization(DRX) for 23Co13Ni11Cr3Mo ultrahigh strength steel.In this model,influences of deformation parameters on hardening rate and solute drag effect were considered.Moreover,an inverse analysis method was proposed for parameters identification of dislocation model and solute drag effect based on the results of isothermal compression tests on Gleeble-1500.Then,simulated microstructures under different deformation conditions were compared with those of experiments.A good agreement is achieved.Furthermore,influences of deformation parameters on microstructure evolution for 23Co13Ni11Cr3Mo steel were investigated in details.High strain is an effective measure to refine grain and improve homogeneity.Meanwhile,the desired deformation parameters are temperature of 1000-1050 °C and strain rate of 0.008-0.01 s-1 for obtaining grains smaller than 22.5 μm.
基金Project(51101052) supported by the National Natural Science Foundation of China
文摘Using the Gleeble-1500 D simulator, the hot deformation behavior and dynamic recrystallization critical conditions of the 10%Ti C/Cu-Al2O3(volume fraction) composite were investigated by compression tests at the temperatures from 450 °C to 850 °C with the strain rates from 0.001 s-1 to 1 s-1. The results show that the softening mechanism of the dynamic recrystallization is a feature of high-temperature flow true stress-strain curves of the composite, and the peak stress increases with the decreasing deformation temperature or the increasing strain rate. The thermal deformation activation energy was calculated as 170.732 k J/mol and the constitutive equation was established. The inflection point in the lnθ-ε curve appears and the minimum value of-(lnθ)/ε-ε curve is presented when the critical state is attained for this composite. The critical strain increases with the increasing strain rate or the decreasing deformation temperature. There is linear relationship between critical strain and peak strain, i.e., εc=0.572εp. The predicting model of critical strain is described by the function of εc=1.062×10-2Z0.0826.
基金Project(52274369)supported by the National Natural Science Foundation of China。
文摘High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material cost poses substantial challenges for optimizing thermal processing parameters through repetitive experimental trials.In this work,hot compression experiments on high-purity silver were conducted using a Gleeble-3800 thermal simulator.The high temperature deformation behaviors,dynamic recovery(DRV)and dynamic recrystallization(DRX)of high-purity silver were studied by constructing an Arrhenius constitutive equation and developing thermal processing maps.The results show that plastic instability of high-purity silver occurs at high strain rates and the optimized hot processing parameters are the strain rate below 0.001 s^(−1) and the temperature of 340−400℃.Microstructural observations exhibit that DRV prefers to occur at lower deformation temperatures(e.g.,250℃).This is attributed to the low stacking fault energy of high-purity silver,which facilitates the decomposition of dislocations into partial dislocations and promotes high-density dislocation accumulation.Furthermore,DRX in high-purity silver becomes increasingly pronounced with increasing deformation temperature and reaches saturation at 350℃.
基金Project(51675465)supported by the National Natural Science Foundation of ChinaProject(E2019203075)supported by the Natural Science Foundation of Hebei Province,China+1 种基金Project(BJ2019001)supported by the Top Young Talents Project of the Education Department of Hebei Province,ChinaProject(Kfkt2017-07)supported by the State Key Laboratory Program of High Performance Complex Manufacturing,China。
文摘The microstructure evolution of 7A85 aluminum alloy at the conditions of strain rate(0.001−1 s^(−1))and deformation temperature(250−450°C)was studied by optical microscopy(OM)and electron back scattering diffraction(EBSD).Based on the K-M dislocation density model,a two-stage K-M dislocation density model of 7A85 aluminum alloy was established.The results reveal that dynamic recovery(DRV)and dynamic recrystallization(DRX)are the main mechanisms of microstructure evolution during thermal deformation of 7A85 aluminum alloy.350−400°C is the transformation zone from dynamic recovery to dynamic recrystallization.At low temperature(≤350°C),DRV is the main mechanism,while DRX mostly occurs at high temperature(≥400°C).At this point,the sensitivity of microstructure evolution to temperature is relatively high.As the temperature increased,the average misorientation angle(θˉ_(c))increased significantly,ranging from 0.93°to 7.13°.Meanwhile,the f_(LAGBs) decreased with the highest decrease of 24%.
基金Project(2012AA03A503) supported by the National High Technology Research and Development Program of China
文摘The dynamic recrystallization and carbides precipitation of the Cr-Co-Mo-Ni bearing steel were investigated by hot compression tests performed at temperatures ranging from 850 ℃to 1080 ℃ with strain rate of 1-20 s-1. The activation energy（Q） for the tested steel is calculated to be around 682.99 k J/mol at a deformation strain of 0.6. Microstructural analysis by SEM shows that the dynamic recrystallization（DRX） behavior is dependent sensitively on the deformation strain, temperature and strain rate, while an exponential relationship between DRX grain size and Z parameter is obtained from the computational formula. Moreover, the M6C-type carbides（〈1 μm） act as the main prohibitor of grain coarsening, and the polynomial regression relationship between them is worked out. With electron backscatter diffraction（EBSD） observation, DRX is the main nucleation mechanism responsible for the formation of new grains during hot compression. In conclusion, the interaction between DRX affected by hot deformation parameters and carbides precipitation determines the ultimate grain size refinement.
基金Project(2016GK1004)supported by the Science and Technology Major Project of Hunan Province,China
文摘The hot deformation behavior of Al-6.2Zn-0.70Mg-0.30Mn-0.17 Zr alloy and its microstructural evolution were investigated by isothermal compression test in the deformation temperature range between 623 and 773 K and the strain rate range between 0.01 and 20 s^(-1).The results show that the flow stress decreased with decreasing strain rate and increasing deformation temperature.At low deformation temperature(≤673 K) and high strain rate(≥1 s^(-1)),the main flow softening was caused by dynamic recovery;conversely,at higher deformation temperature and lower strain rate,the main flow softening was caused by dynamic recrystallization.Moreover,the slipping mechanism transformed from dislocation glide to grain boundary sliding with increasing the deformation temperature and decreasing the strain rate.According to TEM observation,numerous Al_3Zr particles precipitated in matrix,which could effectively inhibit the dynamic recrystallization of the alloy.Based on the processing map,the optimum processing conditions for experimental alloy were in deformation temperature range from 730 K to 773 K and strain rate range from 0.033 s^(-1) to 0.18 s^(-1) with the maximum efficiency of 39%.
基金Projects(51305091,51475101)supported by the National Natural Science Foundation of ChinaProject(20132304120025)supported by Specialized Research Fund for the Doctoral Program of Higher Education,China
文摘In order to present the microstructures of dynamic recrystallization(DRX) in different deformation zones of hot extruded NiTi shape memory alloy(SMA) pipe coupling,a simulation approach combining finite element method(FEM) with cellular automaton(CA) was developed and the relationship between the macroscopic field variables and the microscopic internal variables was established.The results show that there exists a great distinction among the microstructures in different zones of pipe coupling because deformation histories of these regions are diverse.Large plastic deformation may result in fine recrystallized grains,whereas the recrystallized grains may grow very substantially if there is a rigid translation during the deformation,even if the final plastic strain is very large.As a consequence,the deformation history has a significant influence on the evolution path of the DRX as well as the final microstructures of the DRX,including the morphology,the mean grain size and the recrystallization fraction.
文摘ZK60-xcerium alloys were studied,where x mass fraction is 0, 0.52%, 0.94%, 1.51% and 1.98%, respectively. Influence of Ce contents and heat-treatment on microstructure and tensile properties was analyzed. The results show that cast ZK60 alloy containing no Ce has coarse crystal grains, and lots of segregation aggregates around the grain-boundary. However, the alloys containing Ce have refined grains, and grain-boundaries are purified at the same time. Obvious dynamic recrystallization occurs in tested alloys after hot-extrusion. Tensile strength heightens with the increase of Ce content, and grows higher after aging at 150℃ for 024 h （T5 treatment）. Comparing tensile properties of investigated alloys in different states, it can be concluded that synthetical properties of the alloy with 1.51% Ce addition is the best of all. In extruded state, σb and δ of this alloy are 318.6 MPa and 14.4%, respectively. After aging for 24 h ,σb is 338.6 MPa and δ is 15.6%.
基金Project (50275094) supported by the National Natural Science Foundation of China
文摘Single hit compression tests were performed at 1 223-1 473 K and strain rate of 0.1-10 s-1 to study hot deformation behavior and flow stress model of F40MnV steel. The dependence of the peak stress, initial stress, saturation stress, steady state stress and peak stain on Zener-Hollomon parameter were obtained. The mathematical models of dynamic recrystallization fraction and grain size were also obtained. Based on the tested data, the flow stress model of F40MnV steel was established in dynamic recovery region and dynamic recrystallization region, respectively. The results show that the activation energy for dynamic recrystallization is 278.6 kJ/mol by regression analysis. The flow stress model of F40MnV steel is proved to approximate the tested data and suitable for numerical simulation of hot forging.
基金Project(2007BAE38B01) supported by National Science and Technology Pillar Program
文摘The hot-compression of Al-IMn-IMg （mass fraction, %） alloy sample was carried out on a Gleeble-1500 thermo-simulator at deformation temperatures from 320 to 400 ℃ and strain rates from 0.1 to 10 s 1 by total strain of 1.4. Microstructure and texture evolution of the hot-compressed alloy were investigated by optical microscopy and X-ray diffraction analysis, respectively. The results show that the relationship among flow stress a, deformation temperature T and strain rate ε can be expressed in the form of βσ = lnε＋Q/（RT）-lnA. The threshold value of In Z （Z is Zener-Hollomon parameter） characterizing the dynamic recrystallization （DRX） is 46, below which the DRX takes place. A strong P orientation {011}（455） associated with a weak cube orientation { 100} （001） is found in the recrystallized sample during hot-compression.
基金Project(2006BAE04B02-3)supported by the National Key Program of 11th Five-Year Plan of China
文摘The hot deformation simulation of a ZK60 magnesiuln alloy at different temperatures from 373 to 673 K and different strain rates of 0.1, 0.01 and 0.002 s^-1 was studied by using the Gleebe-1500 simulator. The plastic deformation behavior was measured and the deformation activation energy was calculated. The microstructures of ZK60 magnesium alloy with an addition of neodymium during the deformation process were observed by using Polyvar-MET optical microscope and Tecnai G^2 20 TEM. The results show that the working hardening, the dynamic recovery and the dynamic recrystallization occur during the plastic deformation process at different temperatures and strain rates. The dynamic recrystallization starts when the temperature is over 473 K and the DRX grain size after hot deformation is only 5-10 μm. So the refined grains improve both the tensile strength and the elongation of alloys at room temperature. Neodymium is added into the alloy and a precipitate phase Mg12Nd that impedes the movement of dislocations is formed, which benefits to increasing mechanical properties of ZK60 magnesium alloy.
文摘Microstructures and mechanical properties of （Mg-2.0%Ce-0.7%Zn-0.7%Zr） alloy were studied. The results of scanning electron microscopy show that Mg12Ce phase mainly distributes at the grain boundaries. The fine (Mg12Ce) phase can apparently elevate recrystallization temperature by preventing the grain boundary migration. No dynamic recrystallization occurs during the hot-extrusion. The mechanical properties of as extruded specimens are （σb=278.5 MPa,） δ=12.0%, while those of the specimens annealed at 250 ℃ for 100 h are σb=（272.6 MPa,） δ=（11.3%,） which indicate that the alloy has good mechanical properties at room temperature.
