Based on the steady-state strain measured by single-pass hot compression tests,the method by a double-pass hot compression testing was developed to measure the metadynamic-recrystallization kinetics.The metadynamic re...Based on the steady-state strain measured by single-pass hot compression tests,the method by a double-pass hot compression testing was developed to measure the metadynamic-recrystallization kinetics.The metadynamic recrystallization behavior of low-alloy steel Q345B during hot compression deformation was investigated in the temperature range of 1 000-1 100℃,the strain rate range of 0.01-0.10 s -1 and the interpass time range of 0.5-50 s on a Gleeble-3500 thermo-simulation machine.The results show that metadynamic recrystallization during the interpass time can be observed.As the deformation temperature and strain rate increase,softening caused by metadynamic recrystallization is obvious.According to the data of thermo-simulation,the metadynamic recrystallization activation energy is obtained to be Qmd=100.674 kJ/mol and metadynamic recrystallization kinetics model is set up.Finally,the error analysis of metadynamic recrystallization kinetics model proves that the model has high accuracy(correlation coefficient R=0.988 6).展开更多
Structural and electronic properties of Pb_(n)Ag_(n)(n=2–12)clusters were investigated by density functional theory with generalized gradient approximation at BLYP level in DMol3 program package.The optimized bimetal...Structural and electronic properties of Pb_(n)Ag_(n)(n=2–12)clusters were investigated by density functional theory with generalized gradient approximation at BLYP level in DMol3 program package.The optimized bimetallic Pb_(n)Ag_(n)(n=2–12)clusters were viewed as the initial structures,then,those were calculated by ab initio molecular dynamics(AIMD)to search possible global minimum energy structures of Pb_(n)Ag_(n)clusters,finally,the ground state structures of Pb_(n)Ag_(n)(n=2–12)clusters were achieved.According to the structural evolution of lowest energy structures,Ag atoms prefer gather in the central sites while Pb atoms prefer external positions in Pb_(n)Ag_(n)(n=2–12)clusters,which is in excellent agreement with experimental results from literature and the application in metallurgy.The average binding energies,HOMO-LUMO gaps,vertical ionization potentials,vertical electron affinities,chemical hardnessη,HOMO orbits,LUMO orbits and density of states of Pb_(n)Ag_(n)(n=2–12)clusters were calculated.The results indicate that the values of HOMO-LUMO gaps,vertical ionization potentials,vertical electron affinities and chemical hardnessηshow obvious odd-even oscillations when n≤5,Pb_(n)Ag_(n)(n=2–12)clusters become less chemically stable and show insulator-to-metal transition with the variation of cluster size n,Pb_(n)Ag_(n)(n≥9)cluster are good candidates to study the properties of PbAg alloys.Those can be well explained by the density of states(DOS)distributions of Pb atoms and Ag atoms between–0.5 Ha and 0.25 Ha in Pb_(n)Ag_(n)(n=2–12)clusters.展开更多
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 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
基金Project(101048) supported by Fok Ying Tung Education FoundationProject(E2008000835) supported by the Natural Science Foundation of Hebei Province,China
文摘Based on the steady-state strain measured by single-pass hot compression tests,the method by a double-pass hot compression testing was developed to measure the metadynamic-recrystallization kinetics.The metadynamic recrystallization behavior of low-alloy steel Q345B during hot compression deformation was investigated in the temperature range of 1 000-1 100℃,the strain rate range of 0.01-0.10 s -1 and the interpass time range of 0.5-50 s on a Gleeble-3500 thermo-simulation machine.The results show that metadynamic recrystallization during the interpass time can be observed.As the deformation temperature and strain rate increase,softening caused by metadynamic recrystallization is obvious.According to the data of thermo-simulation,the metadynamic recrystallization activation energy is obtained to be Qmd=100.674 kJ/mol and metadynamic recrystallization kinetics model is set up.Finally,the error analysis of metadynamic recrystallization kinetics model proves that the model has high accuracy(correlation coefficient R=0.988 6).
基金Project(51664032)supported by the Regional Foundation of the National Natural Science Foundation of ChinaProject(51474116)supported by the General Program of the National Natural Science Foundation of China+5 种基金Project(U1502271)supported by the Joint Foundation of the NSFC-Yunnan Province,ChinaProject(2014HA003)supported by the Cultivating Plan Program for the Leader in Science and Technology of Yunnan Province,ChinaProject(2014RA4018)supported by the Program for Nonferrous Metals Vacuum Metallurgy Innovation Team of Ministry of Science and Technology,ChinaProject(2016YFC0400404)supported by the National Key Research and Development Program of ChinaProject(51504115)supported by the Youth Program of National Natural Science Foundation of ChinaProject(IRT_17R48)supported by the Program for Innovative Research Team in University of Ministry of Education of China
文摘Structural and electronic properties of Pb_(n)Ag_(n)(n=2–12)clusters were investigated by density functional theory with generalized gradient approximation at BLYP level in DMol3 program package.The optimized bimetallic Pb_(n)Ag_(n)(n=2–12)clusters were viewed as the initial structures,then,those were calculated by ab initio molecular dynamics(AIMD)to search possible global minimum energy structures of Pb_(n)Ag_(n)clusters,finally,the ground state structures of Pb_(n)Ag_(n)(n=2–12)clusters were achieved.According to the structural evolution of lowest energy structures,Ag atoms prefer gather in the central sites while Pb atoms prefer external positions in Pb_(n)Ag_(n)(n=2–12)clusters,which is in excellent agreement with experimental results from literature and the application in metallurgy.The average binding energies,HOMO-LUMO gaps,vertical ionization potentials,vertical electron affinities,chemical hardnessη,HOMO orbits,LUMO orbits and density of states of Pb_(n)Ag_(n)(n=2–12)clusters were calculated.The results indicate that the values of HOMO-LUMO gaps,vertical ionization potentials,vertical electron affinities and chemical hardnessηshow obvious odd-even oscillations when n≤5,Pb_(n)Ag_(n)(n=2–12)clusters become less chemically stable and show insulator-to-metal transition with the variation of cluster size n,Pb_(n)Ag_(n)(n≥9)cluster are good candidates to study the properties of PbAg alloys.Those can be well explained by the density of states(DOS)distributions of Pb atoms and Ag atoms between–0.5 Ha and 0.25 Ha in Pb_(n)Ag_(n)(n=2–12)clusters.
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(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%.
