The existing researches of hot ring rolling process are mainly based on forged billet. Compared with the existing process, the new ring casting-rolling compound forming process has significant advantages in saving mat...The existing researches of hot ring rolling process are mainly based on forged billet. Compared with the existing process, the new ring casting-rolling compound forming process has significant advantages in saving materials and energy, reducing emission and reducing the production cost. The microstructure evolution of the casting materials during hot deformation is the basis of the research of the new process. However, the researches on the casting materials are rare. The metadynamic recrystallization of the as-cast 42CrMo steel after normalizing and tempering during the hot compression is investigated. The tests are performed on the Gleeble-1500 thermal-mechanical simulator. The influence rule of the deformation parameters on the metadynamic recrystallization is obtained by analyzing the experimental data. The kinetic model of the rnetadynamic recrystallization is deduced. The analysis results show that the metadynamic recrystallization fraction increases with the increase of the deformation temperature and the strain rate. The metallographic experiments are used to investigate the influence rule of the deformation parameters on the grain size of the metadynamic recrystallization. The experimental results show that the grain of the metadynamic recrystallization could be refined with the increase of the strain rate and the decrease of the deformation temperature during hot compression. The occurrence of the metadynamic recrystallization during the hot deformation is more difficult in as-cast 42CrMo steel than in forged 42CrMo steel. The research can provide the foundation for the further research of the hot deformation behaviors of the as-cast structure and theoretical support for the new ring casting-rolling compound process.展开更多
The metadynamic recrystallization (MDRX) behavior of as-cast 904L superaustenitic stainless steel was in- vestigated by double pass isothermal compression tests at temperatures of 950-1 150 ℃, strain rates of 0.05-...The metadynamic recrystallization (MDRX) behavior of as-cast 904L superaustenitic stainless steel was in- vestigated by double pass isothermal compression tests at temperatures of 950-1 150 ℃, strain rates of 0.05-5 s 1 and interval of 1-100 s. The effects of working parameters (deformation temperature, strain rate, pre-strain and in- terval time) on the flow curves and microstructural evolution were discussed. The MDRX fraction increased obvious- ly with the increase of deformation temperature, strain rate and interval time. The MDRX softening was controlled by the migration of grain boundary, annihilation of dislocation and dynamic recrystallization. Moreover, the kinetic model was established for the prediction of MDRX behavior of as-cast 904L superaustenitic stainless steel based on the experimental data. A good agreement between the predicted and the experimental values was achieved (correla- tion coefficient R2= 0.98), indicating a satisfactory accuracy.展开更多
Static and metadynamic recrystallization models were developed with the coefficients determined by multiple nonlinear regression analyses to describe microstructure evolution in low carbon steels. The effects of initi...Static and metadynamic recrystallization models were developed with the coefficients determined by multiple nonlinear regression analyses to describe microstructure evolution in low carbon steels. The effects of initial grain size, deformation temperature, strain, and strain rate on the austenitic recrystal-lized volume fraction and grain size were studied using a Gleeble machine. The results show that deformation reduces the grain size when the recrystallized volume fraction is large. The static recrystallized volume fraction increases with increasing deformation temperature, strain, and strain rate, and decreasing initial grain size. The grain size during metadynamic recrystallization is independent of the deformation strain and the initial grain size. The recrystallized volume fraction, the grain size, and the grown grain size calculated by the correlations are consistent with the measured values.展开更多
The effects of the deformation parameters in the heavy reduction(HR)process on recrystallization kinetics and microstructure evolution were analyzed.Based on the experimental results,metadynamic recrystallization(MDRX...The effects of the deformation parameters in the heavy reduction(HR)process on recrystallization kinetics and microstructure evolution were analyzed.Based on the experimental results,metadynamic recrystallization(MDRX)kinetic and austenite grain size models were established for a continuously cast slab during HR.Moreover,the evolution of the quenched microstructure after MDRX was observed using electron backscatter diffraction.The relative frequency of very low-angle grain boundaries decreased from 58.8% to 52.1%,and the relative frequency of high-angle grain boundaries increased from 28.5% to 38.9%.Analyses revealed that the recovery was the main softening mechanism.The decrease in the total grain boundary length indicated that subgrain growth occurred with increasing inter-pass time.The main texture evolved from a {001}<110>texture to a{112}<111>texture,and the texture strength remained unchanged.展开更多
The metadynamic recrystallization(MDRX)model is established,and the coefficients determined by multiple linear regression analysis are used to describe the microstructure evolution of SA508Gr.4N steel.The effects of c...The metadynamic recrystallization(MDRX)model is established,and the coefficients determined by multiple linear regression analysis are used to describe the microstructure evolution of SA508Gr.4N steel.The effects of compression temperature of 950–1150℃,strain rate of 0.001–0.1 s^(-1),pre-strain of 0.3–0.6,initial austenite grain size(IAGS)of 136–552 lm,and interval time of 1–300 s on the MDRX kinetics and microstructure evolution were analyzed,using twopass compression test method on Gleeble thermo-mechanical simulator.The results show that MDRX kinetics and austenite grain size are strongly dependent on compression temperature and strain rate,MDRX volume fraction increases with increasing compression temperature and strain rate,and the grain size decreases with increasing strain rate and decreasing compression temperature,while less affected by the pre-strain and IAGS.Meanwhile,the values predicted using MDRX model and the ones calculated from experiment are compared,and the results show that the proposed model can give a reasonable estimate of MDRX behavior for SA508Gr.4N steel.展开更多
Single-and two-step hot compression experiments were carried out on 16Cr25Ni6Mo superaustenitic stainless steel in the temperature range from 950 to 1150°C and at a strain rate of 0.1 s^(-1). In the two-step te...Single-and two-step hot compression experiments were carried out on 16Cr25Ni6Mo superaustenitic stainless steel in the temperature range from 950 to 1150°C and at a strain rate of 0.1 s^(-1). In the two-step tests, the first pass was interrupted at a strain of 0.2; after an interpass time of 5, 20, 40, 60, or 80 s, the test was resumed. The progress of dynamic recrystallization at the interruption strain was less than 10%. The static softening in the interpass period increased with increasing deformation temperature and increasing interpass time. The static recrystallization was found to be responsible for fast static softening in the temperature range from 950 to 1050°C. However, the gentle static softening at 1100 and 1150°C was attributed to the combination of static and metadynamic recrystallizations. The correlation between calculated fractional softening and microstructural observations showed that approximately 30% of interpass softening could be attributed to the static recovery. The microstructural observations illustrated the formation of fine recrystallized grains at the grain boundaries at longer interpass time. The Avrami kinetics equation was used to establish a relationship between the fractional softening and the interpass period. The activation energy for static softening was determined as 276 kJ/mol.展开更多
The adsorption of protein molecules to oil/water(O/W)interface is of critical importance for the product design in a wide range of technologies and industries such as biotechnology,food industry and pharmaceutical ind...The adsorption of protein molecules to oil/water(O/W)interface is of critical importance for the product design in a wide range of technologies and industries such as biotechnology,food industry and pharmaceutical industry.In this work,with ovalbumin(OVA)as the model protein,the adsorption conformations at the O/W interface and the adsorption stability have been systematically studied via multiple simulation methods,including all-atom molecular dynamic(AAMD)simulations,coarse-grained molecular dynamic(CGMD)simulations and enhanced sampling methods.The computational results of AAMD and CGMD show that the hydrophobic tail of OVA tends to be folded under long time relaxation in aqueous phase,and multiple adsorption conformations can exist at the interface due to heterogeneous interactions raising from oil and water respectively.To further study the adsorption sites of the protein,the adsorption kinetics of OVA at the O/W interface is simulated using metadynamics method combined with CGMD simulations,and the result suggests the existence of multiple adsorption conformations of OVA at interface with the head-on conformation as the most stable one.In all,this work focuses on the adsorption behaviors of OVA at squalene/water interface,and provides a theoretical basis for further functionalization of the proteins in emulsion-based products and engineering.展开更多
A series of tests of deformation-induced ferrite transformation (DIP-T) in a low carbon steel were carried out by the Gleeble-3500 hot simulation machine at a temperature range of Ae3-Ar3. The overall stress-strain ...A series of tests of deformation-induced ferrite transformation (DIP-T) in a low carbon steel were carried out by the Gleeble-3500 hot simulation machine at a temperature range of Ae3-Ar3. The overall stress-strain curves during DIFT can be divided into three typical types: "double-humped"," single-humped" and "transitional". The peaks exhibited in the curve are involved with deformation-induced transformation which happened in grains or at the grain boundaries. According to the stress-time curve and strain-time curve, strain capacity dramatically postponed the strain-induced transformation, which leads to the start of the transformation right ahead of the finish of deformation and the majority of the ferrite transformation process mainly happened after the deformation. Deformation-induced transformation is a metadynamic transformation process with dynamic nucleation.展开更多
Static recrystallization(SRX)behaviors and corresponding recrystallization mechanisms of 7Mo super-austenitic stainless steel were studied under different deformation conditions.The order of influence of deformation p...Static recrystallization(SRX)behaviors and corresponding recrystallization mechanisms of 7Mo super-austenitic stainless steel were studied under different deformation conditions.The order of influence of deformation parameters on static recrystallization behaviors,from high to low,is followed by temperature,first-stage strain and strain rate.Meanwhile,the effect of holding time on static recrystallization behaviors is significantly controlled by temperature.In addition,with the increase in temperature from 1000 to 1200°C,the static recrystallization mechanism evolves from discontinuous static recrystallization and continuous static recrystallization(cSRX)to metadynamic recrystallization and cSRX,and finally to cSRX.The cSRX exists at all temperatures.This is because high stacking fault energy(56 mJ m−2)promotes the movement of dislocations,making the deformation mechanism of this steel is dominated by planar slip of dislocation.Large undissolved sigma precipitates promote static recrystallization through particle-stimulated nucleation.However,small strain-induced precipitates at grain boundaries hinder the nucleation of conventional SRX and the growth of recrystallized grains,while the hindering effect decreases with the increase in temperature.展开更多
The bond breaking and forming in chemical reactions is a typical rare event,which is one of the difficult problems in molecular dynamics simulations.Numerous enhanced sampling methods have been developed to extend the...The bond breaking and forming in chemical reactions is a typical rare event,which is one of the difficult problems in molecular dynamics simulations.Numerous enhanced sampling methods have been developed to extend the time scale covered by molecular simulations.However,the difficulties of obtaining appropriate collective variables from complicated reaction pathways and a controlled sampling over the desired phase space remain as challenges.Herein,we use MetaITS,which combines metadynamics and integrated tempered sampling,to increase the sampling efficiency for chemical reactions.Metadynamics with collective variables obtained by harmonic linear discriminant analysis can efficiently decrease the main energy barrier of chemical reaction.Meanwhile,integrated tempered sampling can enhance the exploration of other degrees of freedom.In this study,we applied the MetaITS method to two transition-metal-catalyzed organic reactions with complicated reaction coordinates.We simulated here a zirconocene-catalyzed propylene polymerization to investigate the regioselectivity and temperature effects.We also studied a Sharpless epoxidation reaction,for which both chiral products are observed through simulation.展开更多
Double-pass hot compression tests were carried out over a wide range of holding time(0–180 s) and Zener-Hollomon parameter(1.6 E15–1.3 E20) to study the deformation behavior of cast Mg-8 Gd-3 Y alloy.The flow cu...Double-pass hot compression tests were carried out over a wide range of holding time(0–180 s) and Zener-Hollomon parameter(1.6 E15–1.3 E20) to study the deformation behavior of cast Mg-8 Gd-3 Y alloy.The flow curves show obvious work hardening and strain softening stages, leading to the peak stress of double-pass hot compression. Holding time and Zener-Hollomon parameter can significantly affect the second pass peak stress. It is found that increasing the holding time can cause a higher peak stress in the second pass deformation. The second pass stress reaches the peak stress of 71 MPa at ZenerHollomom parameter of 1.6 E15. When the parameter rises to 1.3 E20, the second pass peak goes up to237 MPa. In addition, the second pass peak stress is significantly higher than the unloading stress, which is opposite to the flow behavior of aluminum alloys. Residual stored deformation energy caused by the first pass deformation could be consumed by metadynamic recrystallization. Therefore, more strain energy is required for subsequent dynamic recrystallization, resulting in hardening behavior. A hardening fraction is defined to describe the deformation behavior quantitatively, which shows a positive correlation with the metadynamic recrystallization fraction. The metadynamic recrystallization leads to grain growth at the inter pass holding stage, diminishing dynamic recrystallization nucleation positions in the second pass deformation.展开更多
Most current enhanced sampling(ES) algorithms attempt to bias a potential energy surface based on preset slow collective variables to improve simulation efficiency. However, due to difficulty in obtaining slow variabl...Most current enhanced sampling(ES) algorithms attempt to bias a potential energy surface based on preset slow collective variables to improve simulation efficiency. However, due to difficulty in obtaining slow variables in complex molecular systems,approximate slow variables are usually applied in ES, which often fail to achieve the expected high efficiency and sufficient accuracy when reconstructing equilibrium properties. In this paper, we demonstrate that the trajectory mapping(TM) technique has the potential to provide the required slow variables for ES. We illustrate the application of a typical ES algorithm(metadynamics)based on the slow variables constructed from the TM in a hairpin peptide system. In this system, both the equilibrium properties and slow dynamics are accurately obtained within approximately two to three orders of magnitude shorter simulation time than in regular molecular dynamics simulation.展开更多
基金supported by Key Program of National Natural Science Foundation of China (Grant No. 51135007)National Natural Science Foundation of China (Grant No. 51075290)+1 种基金Shanxi Provincial Science and Technology Planning Project of China (Grant No. 20100321083)Shanxi Provincial Foundation for Returnees of China (Grant No.2011011025-1)
文摘The existing researches of hot ring rolling process are mainly based on forged billet. Compared with the existing process, the new ring casting-rolling compound forming process has significant advantages in saving materials and energy, reducing emission and reducing the production cost. The microstructure evolution of the casting materials during hot deformation is the basis of the research of the new process. However, the researches on the casting materials are rare. The metadynamic recrystallization of the as-cast 42CrMo steel after normalizing and tempering during the hot compression is investigated. The tests are performed on the Gleeble-1500 thermal-mechanical simulator. The influence rule of the deformation parameters on the metadynamic recrystallization is obtained by analyzing the experimental data. The kinetic model of the rnetadynamic recrystallization is deduced. The analysis results show that the metadynamic recrystallization fraction increases with the increase of the deformation temperature and the strain rate. The metallographic experiments are used to investigate the influence rule of the deformation parameters on the grain size of the metadynamic recrystallization. The experimental results show that the grain of the metadynamic recrystallization could be refined with the increase of the strain rate and the decrease of the deformation temperature during hot compression. The occurrence of the metadynamic recrystallization during the hot deformation is more difficult in as-cast 42CrMo steel than in forged 42CrMo steel. The research can provide the foundation for the further research of the hot deformation behaviors of the as-cast structure and theoretical support for the new ring casting-rolling compound process.
基金Item Sponsored by National Natural Science Foundation of China(U1460104)Fund of State Key Laboratory of Solidification Processing in NWPU of China(SKLSP201322)
文摘The metadynamic recrystallization (MDRX) behavior of as-cast 904L superaustenitic stainless steel was in- vestigated by double pass isothermal compression tests at temperatures of 950-1 150 ℃, strain rates of 0.05-5 s 1 and interval of 1-100 s. The effects of working parameters (deformation temperature, strain rate, pre-strain and in- terval time) on the flow curves and microstructural evolution were discussed. The MDRX fraction increased obvious- ly with the increase of deformation temperature, strain rate and interval time. The MDRX softening was controlled by the migration of grain boundary, annihilation of dislocation and dynamic recrystallization. Moreover, the kinetic model was established for the prediction of MDRX behavior of as-cast 904L superaustenitic stainless steel based on the experimental data. A good agreement between the predicted and the experimental values was achieved (correla- tion coefficient R2= 0.98), indicating a satisfactory accuracy.
文摘Static and metadynamic recrystallization models were developed with the coefficients determined by multiple nonlinear regression analyses to describe microstructure evolution in low carbon steels. The effects of initial grain size, deformation temperature, strain, and strain rate on the austenitic recrystal-lized volume fraction and grain size were studied using a Gleeble machine. The results show that deformation reduces the grain size when the recrystallized volume fraction is large. The static recrystallized volume fraction increases with increasing deformation temperature, strain, and strain rate, and decreasing initial grain size. The grain size during metadynamic recrystallization is independent of the deformation strain and the initial grain size. The recrystallized volume fraction, the grain size, and the grown grain size calculated by the correlations are consistent with the measured values.
基金financially supported by the National Natural Science Foundation of China(Nos.51974078,U1708259,and U20A20272)Liaoning Revitalization Talents Program(Nos.XLYC1802032 and XLYC1907176)+1 种基金the Fundamental Research Funds for the Central Universities of China(Nos.N2025012,N2125018,and N2125007)the Fourth Period Science and Technology Key Project of Panxi Experimental Area(No.PGWX2018-05).
文摘The effects of the deformation parameters in the heavy reduction(HR)process on recrystallization kinetics and microstructure evolution were analyzed.Based on the experimental results,metadynamic recrystallization(MDRX)kinetic and austenite grain size models were established for a continuously cast slab during HR.Moreover,the evolution of the quenched microstructure after MDRX was observed using electron backscatter diffraction.The relative frequency of very low-angle grain boundaries decreased from 58.8% to 52.1%,and the relative frequency of high-angle grain boundaries increased from 28.5% to 38.9%.Analyses revealed that the recovery was the main softening mechanism.The decrease in the total grain boundary length indicated that subgrain growth occurred with increasing inter-pass time.The main texture evolved from a {001}<110>texture to a{112}<111>texture,and the texture strength remained unchanged.
基金This work was financially supported by the National Energy Application Technology Research and Engineering Demonstrative Project of China(NY201501)the National High Technology Research and Development Program of China(863 Program,No.2012AA03A501)the National Key Research and Development Program of China(2016YFB0300203).
文摘The metadynamic recrystallization(MDRX)model is established,and the coefficients determined by multiple linear regression analysis are used to describe the microstructure evolution of SA508Gr.4N steel.The effects of compression temperature of 950–1150℃,strain rate of 0.001–0.1 s^(-1),pre-strain of 0.3–0.6,initial austenite grain size(IAGS)of 136–552 lm,and interval time of 1–300 s on the MDRX kinetics and microstructure evolution were analyzed,using twopass compression test method on Gleeble thermo-mechanical simulator.The results show that MDRX kinetics and austenite grain size are strongly dependent on compression temperature and strain rate,MDRX volume fraction increases with increasing compression temperature and strain rate,and the grain size decreases with increasing strain rate and decreasing compression temperature,while less affected by the pre-strain and IAGS.Meanwhile,the values predicted using MDRX model and the ones calculated from experiment are compared,and the results show that the proposed model can give a reasonable estimate of MDRX behavior for SA508Gr.4N steel.
文摘Single-and two-step hot compression experiments were carried out on 16Cr25Ni6Mo superaustenitic stainless steel in the temperature range from 950 to 1150°C and at a strain rate of 0.1 s^(-1). In the two-step tests, the first pass was interrupted at a strain of 0.2; after an interpass time of 5, 20, 40, 60, or 80 s, the test was resumed. The progress of dynamic recrystallization at the interruption strain was less than 10%. The static softening in the interpass period increased with increasing deformation temperature and increasing interpass time. The static recrystallization was found to be responsible for fast static softening in the temperature range from 950 to 1050°C. However, the gentle static softening at 1100 and 1150°C was attributed to the combination of static and metadynamic recrystallizations. The correlation between calculated fractional softening and microstructural observations showed that approximately 30% of interpass softening could be attributed to the static recovery. The microstructural observations illustrated the formation of fine recrystallized grains at the grain boundaries at longer interpass time. The Avrami kinetics equation was used to establish a relationship between the fractional softening and the interpass period. The activation energy for static softening was determined as 276 kJ/mol.
基金financially supported by the National Natural Science Foundation of China(Nos.21821005,21973097,92034302,91834303)the Innovation Academy for Green Manufacture,Chinese Academy of Sciences(IAGM-2019-A03,IAGM-2019-A13)Key Research Program of Frontier Science,Chinese Academy of Sciences(QYZDJ-SSW-JSC029)。
文摘The adsorption of protein molecules to oil/water(O/W)interface is of critical importance for the product design in a wide range of technologies and industries such as biotechnology,food industry and pharmaceutical industry.In this work,with ovalbumin(OVA)as the model protein,the adsorption conformations at the O/W interface and the adsorption stability have been systematically studied via multiple simulation methods,including all-atom molecular dynamic(AAMD)simulations,coarse-grained molecular dynamic(CGMD)simulations and enhanced sampling methods.The computational results of AAMD and CGMD show that the hydrophobic tail of OVA tends to be folded under long time relaxation in aqueous phase,and multiple adsorption conformations can exist at the interface due to heterogeneous interactions raising from oil and water respectively.To further study the adsorption sites of the protein,the adsorption kinetics of OVA at the O/W interface is simulated using metadynamics method combined with CGMD simulations,and the result suggests the existence of multiple adsorption conformations of OVA at interface with the head-on conformation as the most stable one.In all,this work focuses on the adsorption behaviors of OVA at squalene/water interface,and provides a theoretical basis for further functionalization of the proteins in emulsion-based products and engineering.
文摘A series of tests of deformation-induced ferrite transformation (DIP-T) in a low carbon steel were carried out by the Gleeble-3500 hot simulation machine at a temperature range of Ae3-Ar3. The overall stress-strain curves during DIFT can be divided into three typical types: "double-humped"," single-humped" and "transitional". The peaks exhibited in the curve are involved with deformation-induced transformation which happened in grains or at the grain boundaries. According to the stress-time curve and strain-time curve, strain capacity dramatically postponed the strain-induced transformation, which leads to the start of the transformation right ahead of the finish of deformation and the majority of the ferrite transformation process mainly happened after the deformation. Deformation-induced transformation is a metadynamic transformation process with dynamic nucleation.
基金supported by National Natural Science Foundation of China(No.U1810207)the Innovation Pilot Project for Fusion of Science,Education and Industry(International Cooperation)from Qilu University of Technology(No.2020KJC-GH03).
文摘Static recrystallization(SRX)behaviors and corresponding recrystallization mechanisms of 7Mo super-austenitic stainless steel were studied under different deformation conditions.The order of influence of deformation parameters on static recrystallization behaviors,from high to low,is followed by temperature,first-stage strain and strain rate.Meanwhile,the effect of holding time on static recrystallization behaviors is significantly controlled by temperature.In addition,with the increase in temperature from 1000 to 1200°C,the static recrystallization mechanism evolves from discontinuous static recrystallization and continuous static recrystallization(cSRX)to metadynamic recrystallization and cSRX,and finally to cSRX.The cSRX exists at all temperatures.This is because high stacking fault energy(56 mJ m−2)promotes the movement of dislocations,making the deformation mechanism of this steel is dominated by planar slip of dislocation.Large undissolved sigma precipitates promote static recrystallization through particle-stimulated nucleation.However,small strain-induced precipitates at grain boundaries hinder the nucleation of conventional SRX and the growth of recrystallized grains,while the hindering effect decreases with the increase in temperature.
基金supported by National Natural Science Foundation of China(grant nos.21927901,21821004,and 21873007 to Y.Q.G.,grant no.21933004 to Y.D.W.,grant nos.22273061 and 22003042 to Y.I.Y.)the Key-Area Research and Development Program of Guangdong Province(grant no.2020B0101350001 to Y.D.W.).
文摘The bond breaking and forming in chemical reactions is a typical rare event,which is one of the difficult problems in molecular dynamics simulations.Numerous enhanced sampling methods have been developed to extend the time scale covered by molecular simulations.However,the difficulties of obtaining appropriate collective variables from complicated reaction pathways and a controlled sampling over the desired phase space remain as challenges.Herein,we use MetaITS,which combines metadynamics and integrated tempered sampling,to increase the sampling efficiency for chemical reactions.Metadynamics with collective variables obtained by harmonic linear discriminant analysis can efficiently decrease the main energy barrier of chemical reaction.Meanwhile,integrated tempered sampling can enhance the exploration of other degrees of freedom.In this study,we applied the MetaITS method to two transition-metal-catalyzed organic reactions with complicated reaction coordinates.We simulated here a zirconocene-catalyzed propylene polymerization to investigate the regioselectivity and temperature effects.We also studied a Sharpless epoxidation reaction,for which both chiral products are observed through simulation.
基金support of the National Key Research and Development Program of China (Grant No. 2016YFB0301103 and No. 2016YFB0101604)the National Natural Science Foundation of China (Grant No. 51601112)the Shanghai Rising-Star Program (Grant No. 17QB1403000)
文摘Double-pass hot compression tests were carried out over a wide range of holding time(0–180 s) and Zener-Hollomon parameter(1.6 E15–1.3 E20) to study the deformation behavior of cast Mg-8 Gd-3 Y alloy.The flow curves show obvious work hardening and strain softening stages, leading to the peak stress of double-pass hot compression. Holding time and Zener-Hollomon parameter can significantly affect the second pass peak stress. It is found that increasing the holding time can cause a higher peak stress in the second pass deformation. The second pass stress reaches the peak stress of 71 MPa at ZenerHollomom parameter of 1.6 E15. When the parameter rises to 1.3 E20, the second pass peak goes up to237 MPa. In addition, the second pass peak stress is significantly higher than the unloading stress, which is opposite to the flow behavior of aluminum alloys. Residual stored deformation energy caused by the first pass deformation could be consumed by metadynamic recrystallization. Therefore, more strain energy is required for subsequent dynamic recrystallization, resulting in hardening behavior. A hardening fraction is defined to describe the deformation behavior quantitatively, which shows a positive correlation with the metadynamic recrystallization fraction. The metadynamic recrystallization leads to grain growth at the inter pass holding stage, diminishing dynamic recrystallization nucleation positions in the second pass deformation.
基金supported by the National Natural Science Foundation of China(Grant No.11574310)
文摘Most current enhanced sampling(ES) algorithms attempt to bias a potential energy surface based on preset slow collective variables to improve simulation efficiency. However, due to difficulty in obtaining slow variables in complex molecular systems,approximate slow variables are usually applied in ES, which often fail to achieve the expected high efficiency and sufficient accuracy when reconstructing equilibrium properties. In this paper, we demonstrate that the trajectory mapping(TM) technique has the potential to provide the required slow variables for ES. We illustrate the application of a typical ES algorithm(metadynamics)based on the slow variables constructed from the TM in a hairpin peptide system. In this system, both the equilibrium properties and slow dynamics are accurately obtained within approximately two to three orders of magnitude shorter simulation time than in regular molecular dynamics simulation.