Systematic understanding on the magnetic field intensity dependent microstructure evolution and re-crystallization behavior in a Co-B eutectic alloy under a constant undercooling(ΔT≈100 K)were carried out.Absent of ...Systematic understanding on the magnetic field intensity dependent microstructure evolution and re-crystallization behavior in a Co-B eutectic alloy under a constant undercooling(ΔT≈100 K)were carried out.Absent of the magnetic field,the comparable size of divorced FCC-Co and Co_(3)B eutectic ellipsoidal grains coexist with a few regular lamellas.When the magnetic field is less than 15 T,the elongated primary FCC-Co dendrites parallel to the magnetic field with the dispersed FCC-Co nano-particles em-bedded within the Co_(3)B matrix occupy the inter-dendrite regions.Once the magnetic field increases to 20 T,the FCC-Co/Co_(2)B anomalous eutectic colonies dominate.The formation mechanism of Co_(2)B phase is discussed from several aspects of the competitive nucleation,the chemical redistribution induced by the thermomagnetic-induced convection and magnetic dipole interaction,and the strain-induced trans-formation.Furthermore,the application of magnetic field is found to promote recrystallization,proved by the lower density of misorientation,the appearance of FCC-Co annealed twins and more Co_(3)B sub-grains.This work could further enrich our knowledge about the magnetic-dependent microstructure evolution and recrystallization process in the undercooled Co-B system and provide guidance for controlling the microstructures and properties under extreme conditions.展开更多
The structure transition inside the Co-81.5at.%B alloy liquid has been studied by an in-situ magnetization measurement.A crossover was observed on the 1/M-T curve during the overheating process,indicating that a liqui...The structure transition inside the Co-81.5at.%B alloy liquid has been studied by an in-situ magnetization measurement.A crossover was observed on the 1/M-T curve during the overheating process,indicating that a liquid-liquid structure transition(LLST)took place in the melt.Based on this information,the effects of LLST on the solidification behavior,microstructure and tribology property were investigated experimentally.The sample solidified with the LLST exhibits significantly different solidification behaviors,i.e.,the nucleation undercooling and the recalescence extent are conspicuously enlarged,and the solidification time is shortened.As a result,the microstructure is effectively refined and homogenized,and the hardness and wear resistance are significantly enhanced.The present work might be helpful for not only theoretically understanding the influence of LLST on the solidification behavior but also providing an alternative approach to tailor the microstructure and properties.展开更多
Phase constitutions,either changed by alloying or by phase transformation,are the key factors to determine the magnetic and mechanical performances of high-entropy alloys(HEAs).Using the AlCoCrFeNi HEA as a candidate ...Phase constitutions,either changed by alloying or by phase transformation,are the key factors to determine the magnetic and mechanical performances of high-entropy alloys(HEAs).Using the AlCoCrFeNi HEA as a candidate alloy,this paper demonstrates the effect of phase transformation on both the mechanical and magnetic properties in the multi-phase system.With increasing heat treatment temperature,the sigma(σ)and face-centered-cubic(FCC)phases disappeared at 1000℃and 1200℃,respectively.Such volume fraction changes ofσ,FCC and body-centered-cubic(BCC)phases have divergent effects on mechanical and magnetic properties.The excellent strength-ductility combination will be achieved as the disappearance ofσphase and formation of FCC phase.As for the magnetic properties,the volume fraction of BCC phase plays a major role in determining its saturation magnetization.When the volume fraction change of BCC phase is not evident,the higher volume fraction of FCC phase will influence its magnetization at 2 T.Our present work might provide insights into analyzing the evolution of both mechanical and magnetic properties of HEAs caused by complex phase transformation.展开更多
While there have been multiple recent reports in the literature focusing on the effects of magnetic field on the phase transformation behaviors,the research conducted with an ultra-high magnetic field greater than 20 ...While there have been multiple recent reports in the literature focusing on the effects of magnetic field on the phase transformation behaviors,the research conducted with an ultra-high magnetic field greater than 20 T is still preliminary.In the current study,the structure evolution of Co-B alloys are experimentally studied with undercooling.The effects of a 25 T magnetic field on the solidification behavior and the subsequent solid-state phase transformation behavior have been investigated.The 25 T magnetic field is confirmed to have little effect on the homogeneous nucleation,but have some influence on the heterogeneous nucleation of Co_(3) B and Co_(23)B6 phases by modifying the wetting angleθ.The decomposition of Co_(23)B6 phase in the subsequent cooling process can be effectively suppressed by applying the 25 T magnetic field.The present work might be helpful for not only theoretically understanding the influence of ultra-high magnetic field on the phase transformation behaviors but a potential technology of field-manipulation of magnetic materials.展开更多
基金Project(51690164)supported by the National Natural Science Foundation of ChinaProject(2019-TS-04)supported by the State Key Laboratory of Solidification Processing,China。
基金supported by the National Natural Science Foundation of China (Nos.51690163,52174375)the Fund of the State Key Laboratory of Solidification Processing in NWPU,China (No.2021-TS-01)+1 种基金the Innovation Capability Support Program of Shaanxi Province,China (No.2020KJXX-073)the Fundamental Research Funds for the Central Universities,China.
基金This work was financially supported by the National Natu-ral Science Foundation of China(Nos.52104386 and 52127807)Shanghai Sailing Program,Xi’an Association for Science and Tech-nology Young Talents Lifting Program,and the State Key Laboratory of Solidification Processing(NPU),China(No.2022-TS-08).We acknowledge the support of the LNCMI-CNRS,member of the Euro-pean Magnetic Field Laboratory(EMFL).We also thank Dr.Zheng from ZKKF(Beijing)Science&Technology Company for supporting the characterization of the materials.
文摘Systematic understanding on the magnetic field intensity dependent microstructure evolution and re-crystallization behavior in a Co-B eutectic alloy under a constant undercooling(ΔT≈100 K)were carried out.Absent of the magnetic field,the comparable size of divorced FCC-Co and Co_(3)B eutectic ellipsoidal grains coexist with a few regular lamellas.When the magnetic field is less than 15 T,the elongated primary FCC-Co dendrites parallel to the magnetic field with the dispersed FCC-Co nano-particles em-bedded within the Co_(3)B matrix occupy the inter-dendrite regions.Once the magnetic field increases to 20 T,the FCC-Co/Co_(2)B anomalous eutectic colonies dominate.The formation mechanism of Co_(2)B phase is discussed from several aspects of the competitive nucleation,the chemical redistribution induced by the thermomagnetic-induced convection and magnetic dipole interaction,and the strain-induced trans-formation.Furthermore,the application of magnetic field is found to promote recrystallization,proved by the lower density of misorientation,the appearance of FCC-Co annealed twins and more Co_(3)B sub-grains.This work could further enrich our knowledge about the magnetic-dependent microstructure evolution and recrystallization process in the undercooled Co-B system and provide guidance for controlling the microstructures and properties under extreme conditions.
基金financially supported by the fund of National Key Laboratory for Precision Hot Processing of Metals(No.6142909200104)Shanghai Sailing Program+2 种基金National Training Program of Innovation and Entrepreneurship for Undergraduates(No.S202010699137)Natural Science Foundation of China(Nos.51690164 and 51801161)the Fundamental Research Funds for the Central Universities。
文摘The structure transition inside the Co-81.5at.%B alloy liquid has been studied by an in-situ magnetization measurement.A crossover was observed on the 1/M-T curve during the overheating process,indicating that a liquid-liquid structure transition(LLST)took place in the melt.Based on this information,the effects of LLST on the solidification behavior,microstructure and tribology property were investigated experimentally.The sample solidified with the LLST exhibits significantly different solidification behaviors,i.e.,the nucleation undercooling and the recalescence extent are conspicuously enlarged,and the solidification time is shortened.As a result,the microstructure is effectively refined and homogenized,and the hardness and wear resistance are significantly enhanced.The present work might be helpful for not only theoretically understanding the influence of LLST on the solidification behavior but also providing an alternative approach to tailor the microstructure and properties.
基金supported by the Natural Science Foundation of China(51774240 and 51690163)the fund of the State Key Laboratory of Solidification Processing in NWPU(2019-TS-04)+1 种基金Innovation Capability Support Program of Shaanxi(2020KJXX-073)the Fundamental Research Funds for the Central Universities。
文摘Phase constitutions,either changed by alloying or by phase transformation,are the key factors to determine the magnetic and mechanical performances of high-entropy alloys(HEAs).Using the AlCoCrFeNi HEA as a candidate alloy,this paper demonstrates the effect of phase transformation on both the mechanical and magnetic properties in the multi-phase system.With increasing heat treatment temperature,the sigma(σ)and face-centered-cubic(FCC)phases disappeared at 1000℃and 1200℃,respectively.Such volume fraction changes ofσ,FCC and body-centered-cubic(BCC)phases have divergent effects on mechanical and magnetic properties.The excellent strength-ductility combination will be achieved as the disappearance ofσphase and formation of FCC phase.As for the magnetic properties,the volume fraction of BCC phase plays a major role in determining its saturation magnetization.When the volume fraction change of BCC phase is not evident,the higher volume fraction of FCC phase will influence its magnetization at 2 T.Our present work might provide insights into analyzing the evolution of both mechanical and magnetic properties of HEAs caused by complex phase transformation.
基金supported by the National Natural Science Foundation of China(No.51690164)the fund of National Key Laboratory for Precision Hot Processing of Metals(6142909200104)+2 种基金National Training Program of Innovation and Entrepreneurship for Undergraduates(S202010699137)the Fundamental Research Funds for the Central Universitiesthe support of the LNCMI-CNRS。
文摘While there have been multiple recent reports in the literature focusing on the effects of magnetic field on the phase transformation behaviors,the research conducted with an ultra-high magnetic field greater than 20 T is still preliminary.In the current study,the structure evolution of Co-B alloys are experimentally studied with undercooling.The effects of a 25 T magnetic field on the solidification behavior and the subsequent solid-state phase transformation behavior have been investigated.The 25 T magnetic field is confirmed to have little effect on the homogeneous nucleation,but have some influence on the heterogeneous nucleation of Co_(3) B and Co_(23)B6 phases by modifying the wetting angleθ.The decomposition of Co_(23)B6 phase in the subsequent cooling process can be effectively suppressed by applying the 25 T magnetic field.The present work might be helpful for not only theoretically understanding the influence of ultra-high magnetic field on the phase transformation behaviors but a potential technology of field-manipulation of magnetic materials.