What effect does electric current do on dislocation evolution of metals keeps being a confusing question to be answered and proved. To this end, the dislocation evolution of a superalloy with electric current was dire...What effect does electric current do on dislocation evolution of metals keeps being a confusing question to be answered and proved. To this end, the dislocation evolution of a superalloy with electric current was directly observed by electrical in-situ transmission electron microscopy in this work. Dislocations annihilation at first and then regeneration was found for the first time, which directly proves the existence of electron force during the electrically-assisted manufacturing. Dislocations regeneration would be driven by the electron force and the resistance softening by the local Joule heating effect. Resultantly,a base could be provided for future electrically-assisted research.展开更多
A constitutive model that can describe the damage evolution of anisotropic metal sheets during the complex forming processes which experience wide stress triaxiality history is essential to accurately predict the defo...A constitutive model that can describe the damage evolution of anisotropic metal sheets during the complex forming processes which experience wide stress triaxiality history is essential to accurately predict the deformation and rupture behaviors of the processes.In this study,a modified Lemaitre damage criterion which couples with the anisotropic Barlat 89 yield function is established.The effects of stress triaxiality,Lode parameter and shear stress on damage accumulation are considered in the constitutive model.The model is numerically implemented and applied to fracture prediction in tensile tests with different stress triaxialities and a complex deformation process with wide stress triaxiality history.The good consistency of predictions and experiments indicates that the modified Lemaitre damage model has excellent fracture prediction ability.Finally,the accuracy of the model is analyzed and discussed.展开更多
It is widely accepted that further development of Pb-free solder alloys for improved processing and in-service properties of next-generation electronics,can be accelerated through a fundamental understanding of phase ...It is widely accepted that further development of Pb-free solder alloys for improved processing and in-service properties of next-generation electronics,can be accelerated through a fundamental understanding of phase transformation and microstructure control in Pb-free solder joints.Advanced characterization techniques including synchrotron radiation provide a comprehensive toolset to measure the composition,crystallography,morphology,and properties of the major components of solder alloys.The research using such techniques is reviewed in detail including the characterization of the eff ects of microalloy additions on the microstructure and properties of Pb-free solder joints,especially those on the intermetallic phases.The discoveries outlined are of scientific and industrial relevance and have implications for new solder alloy composition design and the reliability of lead-free solder joints.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.U1737212 and U1637102)the Natural Science Foundation for Distinguished Young Scholars of Shaanxi Province(No.2019JC-09)。
文摘What effect does electric current do on dislocation evolution of metals keeps being a confusing question to be answered and proved. To this end, the dislocation evolution of a superalloy with electric current was directly observed by electrical in-situ transmission electron microscopy in this work. Dislocations annihilation at first and then regeneration was found for the first time, which directly proves the existence of electron force during the electrically-assisted manufacturing. Dislocations regeneration would be driven by the electron force and the resistance softening by the local Joule heating effect. Resultantly,a base could be provided for future electrically-assisted research.
基金co-supported by the National Science Fund for Distinguished Young Scholars of China(No.51625505)the National Natural Science Foundation of China(Nos.U1910213 and U1937203)the Independent Research Project of State Key Laboratory of Solidification Processing of Northwestern Polytechnical University(No.2019-TZ-02)。
文摘A constitutive model that can describe the damage evolution of anisotropic metal sheets during the complex forming processes which experience wide stress triaxiality history is essential to accurately predict the deformation and rupture behaviors of the processes.In this study,a modified Lemaitre damage criterion which couples with the anisotropic Barlat 89 yield function is established.The effects of stress triaxiality,Lode parameter and shear stress on damage accumulation are considered in the constitutive model.The model is numerically implemented and applied to fracture prediction in tensile tests with different stress triaxialities and a complex deformation process with wide stress triaxiality history.The good consistency of predictions and experiments indicates that the modified Lemaitre damage model has excellent fracture prediction ability.Finally,the accuracy of the model is analyzed and discussed.
基金the funding from the National Natural Science Foundation of China(No.51904352)the Natural Science Foundation of Hunan Province(No.2020JJ5758)+3 种基金the State Key Laboratory of Solidification Processing in NPU(Grant No.SKLSP201904)funding from the University of Queensland-Nihon Superior Collaborative Research Programme(Grant No.2016001895)the Australian Research Council(ARC)Discovery(DP200101949)and Linkage(LP180100595)grantsthe financial support from JSPS KAKENHI(Grant No.JP17H06155)。
文摘It is widely accepted that further development of Pb-free solder alloys for improved processing and in-service properties of next-generation electronics,can be accelerated through a fundamental understanding of phase transformation and microstructure control in Pb-free solder joints.Advanced characterization techniques including synchrotron radiation provide a comprehensive toolset to measure the composition,crystallography,morphology,and properties of the major components of solder alloys.The research using such techniques is reviewed in detail including the characterization of the eff ects of microalloy additions on the microstructure and properties of Pb-free solder joints,especially those on the intermetallic phases.The discoveries outlined are of scientific and industrial relevance and have implications for new solder alloy composition design and the reliability of lead-free solder joints.
