In order to describe and predict the kinetic process of discontinuous dynamic recrystallization （DDRX） during hot workingfor metals with low to medium stacking fault energies quantitatively, a new physically-based m...In order to describe and predict the kinetic process of discontinuous dynamic recrystallization （DDRX） during hot workingfor metals with low to medium stacking fault energies quantitatively, a new physically-based model was proposed by considering thecharacteristics of grain size distribution, capillary effect of initial grain boundaries （GBs） and continuous consumption of GBs. UsingIncoloy 028 alloy as a model system, experiments aiming to provide kinetic data （e.g., the size and volume fraction of recrystallizedgrain） and the associated microstructure were performed. Good agreement is obtained between model predictions and experimentalresults, regarding flow stress, recrystallized fraction and grain size evolution. On this basis, a thermo-kinetic relationship upon thegrowth of recrystallized grain was elucidated, i.e., with increasing thermodynamic driving force, the activation energy barrierdecreases.展开更多
The globularization behavior and mechanism of TC17 alloy with basketweave microstructure were investigated, and the models of dynamic and static globularization kinetics were established. The quantitative and metallog...The globularization behavior and mechanism of TC17 alloy with basketweave microstructure were investigated, and the models of dynamic and static globularization kinetics were established. The quantitative and metallographic results show that the globularization of α phase is sensitive to the parameters of deformation and heat treatment. By EBSD analysis, the formation and evolution mechanisms of intra-α boundaries are related to discontinuous dynamic recrystallization and continuous dynamic recrystallization, which can form α grains with high and low misorientations between neighbour grains after the heat treatment, respectively. Based on the globularization behavior and mechanism, two modified JMAK models are developed to predict the dynamic and static globularization kinetics, and the mean absolute relative errors(MARE) of 10.67% and 13.80% indicate the accuracy of the dynamic and static globularization kinetics models. The results of this work can provide guidance for controlling microstructure of titanium alloy.展开更多
The microstructure evolution of Al-Zn-Mg-Cu alloy was studied by differential scanning calorimetry （DSC） and transmission electron microscopy （TEM） during different rate cooling processes. Based on the DSC results...The microstructure evolution of Al-Zn-Mg-Cu alloy was studied by differential scanning calorimetry （DSC） and transmission electron microscopy （TEM） during different rate cooling processes. Based on the DSC results, the kinetics analysis was carried out. The results indicate that the precipitation of η phase is the predominant transformation for the alloy during the cooling process after the solution treatment. And the η phase nucleates on dispersoids and at grain boundaries. The amount of η phase decreases with increasing cooling rate, and reduces by 75% as the cooling rate increases from 5 to 50 ℃/min. The kinetics of the precipitation of η phase can be described by the Kamamoto transformation model when the cooling rate is a constant.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
During the multi-stage processing of advanced high-strength steels, the austenite-to-ferrite transformation, generally as a precursor of the formation of other non-equilibrium or metastable structures, has a severe ef...During the multi-stage processing of advanced high-strength steels, the austenite-to-ferrite transformation, generally as a precursor of the formation of other non-equilibrium or metastable structures, has a severe effect on the subsequent phase transformations. Herein, a more flexible kinetic and microstructural predictive modeling for the key austenite-to-ferrite transformation of Fe-C-Mn-Si steels was developed,in combination with the classical nucleation theory, the general mixed-mode growth model based on Gibbs energy balance, the microstructural path method and the kinetic framework for grain boundary nucleation. Adopting a bounded, extended matrix space corresponding to a single ferrite grain, both softimpingement and hard-impingement can be naturally included in the current modeling. Accordingly, this model outputs the ferrite volume fraction, the austenite/ferrite interface area per unit volume, and the average grain size of ferrite, which will serve as the input parameters for modeling the subsequent bainite or martensite transformations. Applying the model, this work successfully predicts the experiment measurement of the isothermal austenite-to-ferrite transformation in Fe-0.17 C-0.91 Mn-1.03 Si(wt%) steel at different temperatures and explains why the final-state average grain size of ferrite has a maximum at the moderate annealing temperature. Effectiveness and advantages of the present model are discussed arising from kinetics and thermodynamics accompanied with nucleation, growth and impingement.展开更多
Defining and visualizing the three-dimensional(3 D) structures of pharmaceuticals provides a new and important tool to elucidate the phenomenal behavior and underlying mechanisms of drug delivery systems. The mechanis...Defining and visualizing the three-dimensional(3 D) structures of pharmaceuticals provides a new and important tool to elucidate the phenomenal behavior and underlying mechanisms of drug delivery systems. The mechanism of drug release from complex structured dosage forms, such as bilayer osmotic pump tablets, has not been investigated widely for most solid 3 D structures. In this study, bilayer osmotic pump tablets undergoing dissolution, as well as after dissolution in a desiccated solid state were examined, and visualized by synchrotron radiation micro-computed tomography(SR-μCT). In situ formed 3 D structures at different in vitro drug release states were characterized comprehensively. A distinct movement pattern of NaCl crystals from the push layer to the drug layer was observed, beneath the semi-permeable coating in the desiccated tablet samples. The 3 D structures at different dissolution time revealed that the pushing upsurge in the bilayer osmotic pump tablet was directed via peripheral“roadways”. Typically, different regions of the osmotic front, infiltration region, and dormant region were classified in the push layer during the dissolution of drug from tablet samples. According to the observed3 D microstructures, a “subterranean river model” for the drug release mechanism has been defined to explain the drug release mechanism.展开更多
通过采用双道次热压缩的实验方法,在Gleeble-1500D热模拟机上对铸态30Cr2Ni4MoV钢在高温变形时的静态再结晶软化行为进行研究。根据实验结果,分析变形温度、初始晶粒尺寸以及道次间隔时间等不同工艺参数对铸态30Cr2Ni4MoV钢静态软化行...通过采用双道次热压缩的实验方法,在Gleeble-1500D热模拟机上对铸态30Cr2Ni4MoV钢在高温变形时的静态再结晶软化行为进行研究。根据实验结果,分析变形温度、初始晶粒尺寸以及道次间隔时间等不同工艺参数对铸态30Cr2Ni4MoV钢静态软化行为的影响;构建该铸态材料的静态再结晶动力学模型及晶粒尺寸模型,获得该铸态材料的再结晶激活能为207.39 k J·mol-1。通过实验结果可知：该铸态材料的静态再结晶体积分数随温度的升高、应变的增加、应变速率的加快和道次间隔时间的不断延长而增加,却几乎不受初始晶粒尺寸的影响。对比分析热压缩所得到的实验值与该模型的计算值,验证了所建模型的准确性。展开更多
基金Project(51431008)supported by the National Natural Science Foundation of ChinaProjects(2017YFB0703001,2017YFB0305100)supported by the National Key Research and Development Program of China
文摘In order to describe and predict the kinetic process of discontinuous dynamic recrystallization （DDRX） during hot workingfor metals with low to medium stacking fault energies quantitatively, a new physically-based model was proposed by considering thecharacteristics of grain size distribution, capillary effect of initial grain boundaries （GBs） and continuous consumption of GBs. UsingIncoloy 028 alloy as a model system, experiments aiming to provide kinetic data （e.g., the size and volume fraction of recrystallizedgrain） and the associated microstructure were performed. Good agreement is obtained between model predictions and experimentalresults, regarding flow stress, recrystallized fraction and grain size evolution. On this basis, a thermo-kinetic relationship upon thegrowth of recrystallized grain was elucidated, i.e., with increasing thermodynamic driving force, the activation energy barrierdecreases.
基金the support from the Science Fund for Distinguished Young Scholars from Shaanxi Province, China (No. 2020JC-17)the National Natural Science Foundation of China (No. 51705425)+1 种基金the Research Fund of the State Key Laboratory of Solidification Processing (NWPU), China (No. 2019-QZ-04)the Fundamental Research Funds for the Central Universities, China (No. 3102019PY007)。
文摘The globularization behavior and mechanism of TC17 alloy with basketweave microstructure were investigated, and the models of dynamic and static globularization kinetics were established. The quantitative and metallographic results show that the globularization of α phase is sensitive to the parameters of deformation and heat treatment. By EBSD analysis, the formation and evolution mechanisms of intra-α boundaries are related to discontinuous dynamic recrystallization and continuous dynamic recrystallization, which can form α grains with high and low misorientations between neighbour grains after the heat treatment, respectively. Based on the globularization behavior and mechanism, two modified JMAK models are developed to predict the dynamic and static globularization kinetics, and the mean absolute relative errors(MARE) of 10.67% and 13.80% indicate the accuracy of the dynamic and static globularization kinetics models. The results of this work can provide guidance for controlling microstructure of titanium alloy.
基金Project(50975053) supported by the National Natural Science Foundation of China
文摘The microstructure evolution of Al-Zn-Mg-Cu alloy was studied by differential scanning calorimetry （DSC） and transmission electron microscopy （TEM） during different rate cooling processes. Based on the DSC results, the kinetics analysis was carried out. The results indicate that the precipitation of η phase is the predominant transformation for the alloy during the cooling process after the solution treatment. And the η phase nucleates on dispersoids and at grain boundaries. The amount of η phase decreases with increasing cooling rate, and reduces by 75% as the cooling rate increases from 5 to 50 ℃/min. The kinetics of the precipitation of η phase can be described by the Kamamoto transformation model when the cooling rate is a constant.
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financially supported by the National Key R&D Program of China (Nos. 2017YFB0703001 and 2017YFB0305100)the National Natural Science Foundation of China (Nos. 51134011, 51431008, 51790483 and 51801157)+4 种基金the Fundamental Research Funds for the Central Universities (No. 3102017zy064)the Research Fund of the State Key Laboratory of Solidification Processing (Nos. 117-TZ-2015, 159-QP-2016)the Analytical & Testing Center of Northwestern Polytechnical University for Equipment Supportfinancial support from the Top International University Visiting Program for Outstanding Young Scholars of Northwestern Polytechnical Universitythe China Scholarship Council (CSC) Scholarship
文摘During the multi-stage processing of advanced high-strength steels, the austenite-to-ferrite transformation, generally as a precursor of the formation of other non-equilibrium or metastable structures, has a severe effect on the subsequent phase transformations. Herein, a more flexible kinetic and microstructural predictive modeling for the key austenite-to-ferrite transformation of Fe-C-Mn-Si steels was developed,in combination with the classical nucleation theory, the general mixed-mode growth model based on Gibbs energy balance, the microstructural path method and the kinetic framework for grain boundary nucleation. Adopting a bounded, extended matrix space corresponding to a single ferrite grain, both softimpingement and hard-impingement can be naturally included in the current modeling. Accordingly, this model outputs the ferrite volume fraction, the austenite/ferrite interface area per unit volume, and the average grain size of ferrite, which will serve as the input parameters for modeling the subsequent bainite or martensite transformations. Applying the model, this work successfully predicts the experiment measurement of the isothermal austenite-to-ferrite transformation in Fe-0.17 C-0.91 Mn-1.03 Si(wt%) steel at different temperatures and explains why the final-state average grain size of ferrite has a maximum at the moderate annealing temperature. Effectiveness and advantages of the present model are discussed arising from kinetics and thermodynamics accompanied with nucleation, growth and impingement.
基金National Basic Research Program of China (2009CB623200)National Natural Science foundation of China (NSFC 50838008)the Doctoral Program of Higher Education (20070335087)
基金the National Nature Science Foundation of China (Nos.81803446,81803441 and 81773645)Key Program for International Science and Technology Cooperation Projects of China (2020YFE0201700)the Youth Innovation Promotion Association of CAS (2018323)。
文摘Defining and visualizing the three-dimensional(3 D) structures of pharmaceuticals provides a new and important tool to elucidate the phenomenal behavior and underlying mechanisms of drug delivery systems. The mechanism of drug release from complex structured dosage forms, such as bilayer osmotic pump tablets, has not been investigated widely for most solid 3 D structures. In this study, bilayer osmotic pump tablets undergoing dissolution, as well as after dissolution in a desiccated solid state were examined, and visualized by synchrotron radiation micro-computed tomography(SR-μCT). In situ formed 3 D structures at different in vitro drug release states were characterized comprehensively. A distinct movement pattern of NaCl crystals from the push layer to the drug layer was observed, beneath the semi-permeable coating in the desiccated tablet samples. The 3 D structures at different dissolution time revealed that the pushing upsurge in the bilayer osmotic pump tablet was directed via peripheral“roadways”. Typically, different regions of the osmotic front, infiltration region, and dormant region were classified in the push layer during the dissolution of drug from tablet samples. According to the observed3 D microstructures, a “subterranean river model” for the drug release mechanism has been defined to explain the drug release mechanism.
文摘通过采用双道次热压缩的实验方法,在Gleeble-1500D热模拟机上对铸态30Cr2Ni4MoV钢在高温变形时的静态再结晶软化行为进行研究。根据实验结果,分析变形温度、初始晶粒尺寸以及道次间隔时间等不同工艺参数对铸态30Cr2Ni4MoV钢静态软化行为的影响;构建该铸态材料的静态再结晶动力学模型及晶粒尺寸模型,获得该铸态材料的再结晶激活能为207.39 k J·mol-1。通过实验结果可知：该铸态材料的静态再结晶体积分数随温度的升高、应变的增加、应变速率的加快和道次间隔时间的不断延长而增加,却几乎不受初始晶粒尺寸的影响。对比分析热压缩所得到的实验值与该模型的计算值,验证了所建模型的准确性。
