Four Sm_(2)Co_(17)magnets with spin-reorientation transition(SRT)of cell boundary phases(CBPs)are prepared by liquid-phase sintering.The temperature of the SRT of CBPs(T_(SR)^(1:5))is regulated from 125 K to 195 K by ...Four Sm_(2)Co_(17)magnets with spin-reorientation transition(SRT)of cell boundary phases(CBPs)are prepared by liquid-phase sintering.The temperature of the SRT of CBPs(T_(SR)^(1:5))is regulated from 125 K to 195 K by adding 0 wt.%,3 wt.%,6 wt.%and 9 wt.%Dy_(88)Cu_(12)alloy powder.The effect of SRT of Sm_(2)Co_(17)magnet CBPs on the temperature dependence of the magnetization(M-T)and coercivity(H-T)is systematically investigated.The temperature dependence of the magnetization is influenced by the SRT of CBPs.The M-T curves measured during the heating process are larger than those measured during the cooling process when T<T_(SR)^(1:5).When T=T_(SR)^(1:5)there is a bifurcation point.When T>T_(SR)^(1:5)the M-T curves overlap and the M-T derivation curve shows that the magnetization of the magnet has low temperature dependence of magnetization above T_(SR)^(1:5).With increasing T_(SR)^(1:5),the initial temperature of the low temperature dependence of magnetization shifts towards a higher temperature.The coercivity temperature coefficient becomes positive as the SRT effect increases,and the temperature range of the positive coercivity temperature coefficient moves towards higher temperatures as T_(SR)^(1:5)increases.This reveals that SRT of CBPs has little effect on the temperature dependence of magnetization above T_(SR)^(1:5),while the temperature dependence of coercivity is optimized.The temperature range of magnetization and coercivity with low temperature dependence tends towards higher temperatures,which is conducive to the preparation of magnets with a low temperature coefficient at higher temperatures.展开更多
Bulk anisotropic Sm_(2)Co_(7) nanocrystalline magnets were successfully prepared by hot deformation process using spark plasma sintering technology.The coercivity of the isotropic Sm_(2)Co_(7) nanocrystalline magnet i...Bulk anisotropic Sm_(2)Co_(7) nanocrystalline magnets were successfully prepared by hot deformation process using spark plasma sintering technology.The coercivity of the isotropic Sm_(2)Co_(7) nanocrystalline magnet is 34.76 kOe,further,the ultra-high coercivity of 50.68 kOe is obtained in the anisotropic hot deformed Sm_(2)Co_(7) magnet when the height reduction is70%,which is much higher than those of the ordinarily produced hot deformed Sm_(2)Co_(7) magnet.X-ray diffraction(XRD)analysis shows that all the samples are Sm_(2)Co_(7) single phase.The investigation by electron backscatter diffraction indicates that increasing the amount of deformation is beneficial to the improvement of the(001) texture of Sm_(2)Co_(7) magnets.The Sm_(2)Co_(7) nanocrystalline magnet generates a strong c-axis crystallographic texture during large deformation process.展开更多
The high-temperature magnetic perfo rmance and micro structure of Sm_(1-x)Gd_(x)(Co_(bal)Fe_(0.09)Cu_(0.09)Zr_(0.025))_(7.2)(x=0.3,0.5) magnets were investigated.With the isothermal aging time decreasing from 11 to 3 ...The high-temperature magnetic perfo rmance and micro structure of Sm_(1-x)Gd_(x)(Co_(bal)Fe_(0.09)Cu_(0.09)Zr_(0.025))_(7.2)(x=0.3,0.5) magnets were investigated.With the isothermal aging time decreasing from 11 to 3 h,the temperature coefficient of intrinsic coercivity in the temperature range of 25-500℃,β_(25-500℃),was optimized from -0,167%/℃ to-0.112%/℃ for x=0.3 magnets.The noticeable enhancement(~33%) of temperature stability is correlated with the increased content of 1:5H cell boundary phase and its relatively high Curie temperature as well.However,for the x=0.5 magnet,it is found that the presence of Sm_(5)Co_(19) phases and wider nanotwin variants hinder the formation of 1:5H cell boundary phase.The insufficient 1:5H is not beneficial to the proper redistribution of Cu in cell boundary,making the x=0.5 magnet difficult to achieve higher temperature stability.Consequently,the approach of adjusting the isothermal aging process can offer guidance for attaining superior magnetic performance in the temperature range from 25 to 500℃ for Gd-substituted Sm_(2)Co_(17)-type magnets.展开更多
The unique cellular microstructure of Fe-rich Sm_(2)Co_(17)-type permanent magnets is closely associated with the structure of the solid solution precursor.We investigate the phase structure,magnetic properties,and me...The unique cellular microstructure of Fe-rich Sm_(2)Co_(17)-type permanent magnets is closely associated with the structure of the solid solution precursor.We investigate the phase structure,magnetic properties,and mechanical behavior of B-doped Sm_(2)Co_(17)-type magnets with high Fe content.The doped B atoms can diffuse into the interstitial vacancy,resulting in lattice expansion and promote the homogenization of the phase organizational structure during the solid solution treatment in theory.However,the resulting second phase plays a dominant role to result in more microtwin structures and highly ordered 2:17R phases in the solid solution stage,which inhibits the ordering transformation of 1:7H phase during aging and affects the generation of the cellular structure,and to result in a decrease in magnetic properties,yet the interface formed between it and the matrix phase hinders the movement of dislocations and enhances the mechanical properties.Hence,the precipitation of high flexural strain grain boundary phase induced by B element doping is also a new and effective way to improve the flexural strain of Sm_(2)Co_(17)-type magnets.Our study provides a new understanding of the phase structure evolution and its effect on the magnetic and mechanical properties of Sm_(2)Co_(17)-type magnets with high Fe content.展开更多
The excellent thermal stability of magnetic properties of Sm_(2)Co_(17)-based magnets is their most impor-tant feature.However,this stability is reduced when the maximum energy product of Sm_(2)Co_(17)-based magnets i...The excellent thermal stability of magnetic properties of Sm_(2)Co_(17)-based magnets is their most impor-tant feature.However,this stability is reduced when the maximum energy product of Sm_(2)Co_(17)-based magnets is improved,which is mainly determined by the Fe/Cu distribution of the 2:17R cell and 1:5H cell boundary phases.During the demagnetization process,the Cu-rich 1:5H cell boundary phase with a width of 2-15 nm obstructs the motion of the domain walls,yielding coercivity.Herein,we report a micron-scale Cu/Zr-rich and Fe-lean 1:5H-based precipitated phase with a lamellar structure,probably induced by Sm_(2)O_(3) doping.This structure enables the separate regulation of Fe and Cu distribution for Sm_(2)Co_(17)-based magnets with Fe-rich 2:17R cell phases and Cu-rich 1:5H cell boundary phases,consid-erably optimizing the thermal stability of magnetic properties.This discovery can be further developed to produce Sm_(2)Co_(17)-based magnets with high performance and excellent thermal stability of magnetic properties.展开更多
Cu-rich cell boundary phase is difficult to precipitate evenly,resulting in a generally poor demagnetization curve squareness for Fe-rich Sm_(2)Co_(17)-type magnet,which is a key factor limiting the further improvemen...Cu-rich cell boundary phase is difficult to precipitate evenly,resulting in a generally poor demagnetization curve squareness for Fe-rich Sm_(2)Co_(17)-type magnet,which is a key factor limiting the further improvement of magnetic energy product.In this study,we report that nanoscale strip-like ordered micro-domains distributed in1:7H disordered matrix phase of the solid solution precursor is a new factor significantly affecting the precipitation and distribution of the cell boundary phase.Long strip-like and continuous micro-twin structure with twin boundaries neatly perpendicular to the C-axis is observed after sintering treatment.After solution treatment,sequential and long strip-like micro-twins gradually transform into disordered state along the basal plane,forming narrow disordered 1:7H(TbCu_(7)-type structure)phase between the separated strip-like ordered micro-domains.This disordering transformation takes place via broken down of the long strip-like ordered micro-domains,which is accomplished by narrowing along the width direction followed by reduction of the length.Furthermore,a new model revealing the effect of the ordered micro-domains on the formation of the cell boundary phase is proposed.Antiphase boundaries enriched in Cu have already existed in the precursor with long strip-like ordered micro-domains.Therefore,the Cu-rich cell boundary phase acting as strong pinning centers cannot be precipitated homogeneously and distributed continuously after aging,resulting in a poor demagnetization curve squareness of Sm_(2)Co_(17)-type magnet.Our results indicate that significant broken down of the nanoscale ordered micro-domains in solution precursor is the key factor improving the distribution of cell boundary phase in Sm_(2)Co_(17)-type magnets.展开更多
The synthesis of size-controlled Sm_(2)Fe_(17) magnetic particles is a prerequisite for the fabrication of highperformance Sm_(2)Fe_(17)N_(3) permanent magnetic materials.Here,Sm_(2)Fe_(17) was synthesized using a cos...The synthesis of size-controlled Sm_(2)Fe_(17) magnetic particles is a prerequisite for the fabrication of highperformance Sm_(2)Fe_(17)N_(3) permanent magnetic materials.Here,Sm_(2)Fe_(17) was synthesized using a costeffective reduction-diffusion method.The calcium chloride molten salt was introduced to control the particle size and achieve a single phase of Sm_(2)Fe_(17).The effects of reduction-diffusion reaction temperature and the amount of added calcium chloride on the phase constitution and microstructure of the final product of reduction-diffusion were systematically investigated.Adding an appropriate amount of calcium chloride can effectively inhibit the overgrowth and sintering of the reduced particles.By employing the strategy of adding 20 wt% of calcium chlorides into the green compacts,we were able to successfully synthesize uniform Sm_(2)Fe_(17) particles that are well-dispersed,with an average size of 2.2 μm.Furthermore,by combining the optimal reduction-diffusion conditions and the nitriding process,the hard magnetic Sm_(2)Fe_(17)N_(3) material was successfully obtained.This study could be useful for the development of high-performance Sm_(2)Fe_(17)N_(3) magnetic materials utilizing reduction-diffusion technology.展开更多
The microstructure of twinning as well as the phase boundary between 1:5 H and 2:17 R phase in Fe-rich Sm_(2)Co_(17)-type magnets was characterized at atomic scale using nanobeam diffraction and highresolution STEM-HA...The microstructure of twinning as well as the phase boundary between 1:5 H and 2:17 R phase in Fe-rich Sm_(2)Co_(17)-type magnets was characterized at atomic scale using nanobeam diffraction and highresolution STEM-HAADF imaging,and the reason for the dramatic increase of coercivity during slow cooling was investigated based on the microchemistry analysis.The twinning relationship in the 2:17 R phase originates from ordered substitution of Sm atoms by Co-Co atomic pairs on every three(3033)and(3033)planes,leading to formation of two corresponding equivalent twin variants.The basal plane of the 2:17 R phase,the 1:3 R platelet phase across the 2:17 R cell and the 1:5 H cell boundary phase between two adjacent 2:17 R cells all can act as effective twin boundary.The cell boundary phase is precipitated along the pyramidal habit plane,and a fully coherent phase boundary(PB)is formed between the 1:5 H and 2:17 R phases with the orientation relationship to be PB//(1121)1:5 H//(1011)_(2):17 R.The phase boundary may either be parallel to or intersect with the pyramidal planes occupied by Co-Co atomic pairs.The substantial increase of coercivity during slow cooling is ascribed to the development of large gradient of the elements concentration within the cell boundary phase,resulting in large gradient of domain wall energy,and thus the pinning strength of the cell boundary phase against magnetic domain wall motion is significantly enhanced.展开更多
The as-solution-treated Sm_(2)Co_(17)-type magnets exhibiting a single 1:7 H phase with different average grain sizes(D) were designed.Anisotropy of bending strength(R_(bb))and compressive strength(R_(mc)) of the magn...The as-solution-treated Sm_(2)Co_(17)-type magnets exhibiting a single 1:7 H phase with different average grain sizes(D) were designed.Anisotropy of bending strength(R_(bb))and compressive strength(R_(mc)) of the magnets were investigated.Moreover,the R_(bb) increases from 86 to 173 MPa with D decreasing from~52 to~18 μm for group c//h samples.The Hall-Petch correlation was employed to reveal the effect of grain size on mechanical properties of the magnets,giving deep understanding of the mechanical anisotropy characteristics.The relatively high Hall-Petch coefficient K^(Rbb)(0.79 MPa·m^(1/2)) gives rise to the largest R_(bb)(173 MPa) for group c//h samples.The mechanical anisotropy of the samples is well explained based on crystal structure and grain size features(grain boundaries).Grain refinement is an effective way to enhance the mechanical properties of Sm_(2)Co_(17)-type sintered magnets.展开更多
It is confirmed that the solid solution temperature range to obtain optimal magnetic properties is different for the magnets with different Fe contents,and the correlation between magnetic properties and microstructur...It is confirmed that the solid solution temperature range to obtain optimal magnetic properties is different for the magnets with different Fe contents,and the correlation between magnetic properties and microstructures influenced by solid solution temperature(Ts)has been systematically studied.The optimal solid solution temperature range is 1413-1463 K for the Sm(Co_(bal)Fe_(0.213)Cu_(0.073)Zr_(0.024))_(7.6)magnet,which is higher than that of the Sm(Co_(bal)Fe_(0.262)Cu_(0.073)Zr_(0.024))_(7.6)magnet(1403-1453 K),and the optimal T_s range is about 50 K for both of the magnets.The solid solution temperature range shifting toward relatively high temperature is due to the increase in a phase transition temperature.The magnet solution-treated at proper temperature exhibits 1:7 H single phase,and intact cell structure and high Cu concentration(23.12 at%)in the cell boundary are found after aging process,which makes the magnet shows high intrinsic coercivity(H_(cj))and magnetic field at knee-point(H_(knee)).At a lower solid solution temperature,the 2:17 H,1:5 H and Zr-rich precipitation phases appear,which affects the cell structure,density of lamellar phase and Cu concentration in the cell boundary,leading to the reduced magnetic properties.However,at a higher solid solution temperature,there exist obviously light gray and dark regions with different Sm,Cu and Fe contents in scanning electron microscopy observation,and the magnet shows low pinning field in the two regions and incomplete cell structure,resulting in an inferior H_(cj)and H_(knee).展开更多
基金Project supported by the National Key R&D Program of China (Grant Nos.2021YFB3803003 and 2021YFB3503101)Youth Innovation Promotion Association of CAS (Grant No.2023311)+1 种基金Major Project of‘Science and Technology Innovation 2025’in Ningbo (Grant No.2020Z044)Zhejiang Provincial Key Research and Development Program (Grant No.2021C01172)。
文摘Four Sm_(2)Co_(17)magnets with spin-reorientation transition(SRT)of cell boundary phases(CBPs)are prepared by liquid-phase sintering.The temperature of the SRT of CBPs(T_(SR)^(1:5))is regulated from 125 K to 195 K by adding 0 wt.%,3 wt.%,6 wt.%and 9 wt.%Dy_(88)Cu_(12)alloy powder.The effect of SRT of Sm_(2)Co_(17)magnet CBPs on the temperature dependence of the magnetization(M-T)and coercivity(H-T)is systematically investigated.The temperature dependence of the magnetization is influenced by the SRT of CBPs.The M-T curves measured during the heating process are larger than those measured during the cooling process when T<T_(SR)^(1:5).When T=T_(SR)^(1:5)there is a bifurcation point.When T>T_(SR)^(1:5)the M-T curves overlap and the M-T derivation curve shows that the magnetization of the magnet has low temperature dependence of magnetization above T_(SR)^(1:5).With increasing T_(SR)^(1:5),the initial temperature of the low temperature dependence of magnetization shifts towards a higher temperature.The coercivity temperature coefficient becomes positive as the SRT effect increases,and the temperature range of the positive coercivity temperature coefficient moves towards higher temperatures as T_(SR)^(1:5)increases.This reveals that SRT of CBPs has little effect on the temperature dependence of magnetization above T_(SR)^(1:5),while the temperature dependence of coercivity is optimized.The temperature range of magnetization and coercivity with low temperature dependence tends towards higher temperatures,which is conducive to the preparation of magnets with a low temperature coefficient at higher temperatures.
基金Project supports by the Science Center of the National Natural Science Foundation of China(Grant No.52088101)the National Natural Foundation of China(Grant No.51590880)+2 种基金the Fujian Institute of Innovation,Chinese Academy of Sciences(Grant No.FJCXY18040302)the Key Program of the Chinese Academy of Sciences(Grant No.KJZD-EW-M05-1)the Natural Science Foundation of Inner Mongolia,China(Grant Nos.2018LH05006 and2018LH05011)。
文摘Bulk anisotropic Sm_(2)Co_(7) nanocrystalline magnets were successfully prepared by hot deformation process using spark plasma sintering technology.The coercivity of the isotropic Sm_(2)Co_(7) nanocrystalline magnet is 34.76 kOe,further,the ultra-high coercivity of 50.68 kOe is obtained in the anisotropic hot deformed Sm_(2)Co_(7) magnet when the height reduction is70%,which is much higher than those of the ordinarily produced hot deformed Sm_(2)Co_(7) magnet.X-ray diffraction(XRD)analysis shows that all the samples are Sm_(2)Co_(7) single phase.The investigation by electron backscatter diffraction indicates that increasing the amount of deformation is beneficial to the improvement of the(001) texture of Sm_(2)Co_(7) magnets.The Sm_(2)Co_(7) nanocrystalline magnet generates a strong c-axis crystallographic texture during large deformation process.
基金Project supported by the National Key Research and Development Program of China (2021YFB3503100,2022YFB3505303,2021YFB3501500)the Key Technology Research and Development Program of Shandong Province (2019JZZY020210)。
文摘The high-temperature magnetic perfo rmance and micro structure of Sm_(1-x)Gd_(x)(Co_(bal)Fe_(0.09)Cu_(0.09)Zr_(0.025))_(7.2)(x=0.3,0.5) magnets were investigated.With the isothermal aging time decreasing from 11 to 3 h,the temperature coefficient of intrinsic coercivity in the temperature range of 25-500℃,β_(25-500℃),was optimized from -0,167%/℃ to-0.112%/℃ for x=0.3 magnets.The noticeable enhancement(~33%) of temperature stability is correlated with the increased content of 1:5H cell boundary phase and its relatively high Curie temperature as well.However,for the x=0.5 magnet,it is found that the presence of Sm_(5)Co_(19) phases and wider nanotwin variants hinder the formation of 1:5H cell boundary phase.The insufficient 1:5H is not beneficial to the proper redistribution of Cu in cell boundary,making the x=0.5 magnet difficult to achieve higher temperature stability.Consequently,the approach of adjusting the isothermal aging process can offer guidance for attaining superior magnetic performance in the temperature range from 25 to 500℃ for Gd-substituted Sm_(2)Co_(17)-type magnets.
基金the NationalKey R&D Program of China (Grant Nos. 2021YFB3503102and 2022YFB3505301)Science and Technology Innovation2025 Major Project of Ningbo (Grant No. 2022Z204)+2 种基金ZhejiangProvincial Natural Science Foundation Youth OriginalProject (Grant No. LDQ24E010001)the Key R&D Programof Shanxi Province (Grant No. 202302050201014)Ningbo Natural Science Foundation (Grant No. 2021J216).
文摘The unique cellular microstructure of Fe-rich Sm_(2)Co_(17)-type permanent magnets is closely associated with the structure of the solid solution precursor.We investigate the phase structure,magnetic properties,and mechanical behavior of B-doped Sm_(2)Co_(17)-type magnets with high Fe content.The doped B atoms can diffuse into the interstitial vacancy,resulting in lattice expansion and promote the homogenization of the phase organizational structure during the solid solution treatment in theory.However,the resulting second phase plays a dominant role to result in more microtwin structures and highly ordered 2:17R phases in the solid solution stage,which inhibits the ordering transformation of 1:7H phase during aging and affects the generation of the cellular structure,and to result in a decrease in magnetic properties,yet the interface formed between it and the matrix phase hinders the movement of dislocations and enhances the mechanical properties.Hence,the precipitation of high flexural strain grain boundary phase induced by B element doping is also a new and effective way to improve the flexural strain of Sm_(2)Co_(17)-type magnets.Our study provides a new understanding of the phase structure evolution and its effect on the magnetic and mechanical properties of Sm_(2)Co_(17)-type magnets with high Fe content.
基金supported by the National Key R&D Program of China (No.2021YFB3501600)the Key R&D Program of Zhejiang Province (Nos.2021C01191 and 2021C01190).
文摘The excellent thermal stability of magnetic properties of Sm_(2)Co_(17)-based magnets is their most impor-tant feature.However,this stability is reduced when the maximum energy product of Sm_(2)Co_(17)-based magnets is improved,which is mainly determined by the Fe/Cu distribution of the 2:17R cell and 1:5H cell boundary phases.During the demagnetization process,the Cu-rich 1:5H cell boundary phase with a width of 2-15 nm obstructs the motion of the domain walls,yielding coercivity.Herein,we report a micron-scale Cu/Zr-rich and Fe-lean 1:5H-based precipitated phase with a lamellar structure,probably induced by Sm_(2)O_(3) doping.This structure enables the separate regulation of Fe and Cu distribution for Sm_(2)Co_(17)-based magnets with Fe-rich 2:17R cell phases and Cu-rich 1:5H cell boundary phases,consid-erably optimizing the thermal stability of magnetic properties.This discovery can be further developed to produce Sm_(2)Co_(17)-based magnets with high performance and excellent thermal stability of magnetic properties.
基金financially supported by the National Key R&D Program of China(No.2021YFB3503102)Zhejiang Provincial Key R&D Program(No.2021C01191)+2 种基金Science and Technology Innovation 2025 Major Project of Ningbo(No.2020Z037)Ningbo Key R&D Program(No.20222ZDYF020027)Ningbo Natural Science Foundation(No.2021J216)。
文摘Cu-rich cell boundary phase is difficult to precipitate evenly,resulting in a generally poor demagnetization curve squareness for Fe-rich Sm_(2)Co_(17)-type magnet,which is a key factor limiting the further improvement of magnetic energy product.In this study,we report that nanoscale strip-like ordered micro-domains distributed in1:7H disordered matrix phase of the solid solution precursor is a new factor significantly affecting the precipitation and distribution of the cell boundary phase.Long strip-like and continuous micro-twin structure with twin boundaries neatly perpendicular to the C-axis is observed after sintering treatment.After solution treatment,sequential and long strip-like micro-twins gradually transform into disordered state along the basal plane,forming narrow disordered 1:7H(TbCu_(7)-type structure)phase between the separated strip-like ordered micro-domains.This disordering transformation takes place via broken down of the long strip-like ordered micro-domains,which is accomplished by narrowing along the width direction followed by reduction of the length.Furthermore,a new model revealing the effect of the ordered micro-domains on the formation of the cell boundary phase is proposed.Antiphase boundaries enriched in Cu have already existed in the precursor with long strip-like ordered micro-domains.Therefore,the Cu-rich cell boundary phase acting as strong pinning centers cannot be precipitated homogeneously and distributed continuously after aging,resulting in a poor demagnetization curve squareness of Sm_(2)Co_(17)-type magnet.Our results indicate that significant broken down of the nanoscale ordered micro-domains in solution precursor is the key factor improving the distribution of cell boundary phase in Sm_(2)Co_(17)-type magnets.
基金Project supported by the National Natural Science Foundation of China (52201199,52271161)the Program of Top Disciplines Construction in Beijing (PXM2019_014204_500031)。
文摘The synthesis of size-controlled Sm_(2)Fe_(17) magnetic particles is a prerequisite for the fabrication of highperformance Sm_(2)Fe_(17)N_(3) permanent magnetic materials.Here,Sm_(2)Fe_(17) was synthesized using a costeffective reduction-diffusion method.The calcium chloride molten salt was introduced to control the particle size and achieve a single phase of Sm_(2)Fe_(17).The effects of reduction-diffusion reaction temperature and the amount of added calcium chloride on the phase constitution and microstructure of the final product of reduction-diffusion were systematically investigated.Adding an appropriate amount of calcium chloride can effectively inhibit the overgrowth and sintering of the reduced particles.By employing the strategy of adding 20 wt% of calcium chlorides into the green compacts,we were able to successfully synthesize uniform Sm_(2)Fe_(17) particles that are well-dispersed,with an average size of 2.2 μm.Furthermore,by combining the optimal reduction-diffusion conditions and the nitriding process,the hard magnetic Sm_(2)Fe_(17)N_(3) material was successfully obtained.This study could be useful for the development of high-performance Sm_(2)Fe_(17)N_(3) magnetic materials utilizing reduction-diffusion technology.
基金Project supported by Zhejiang Province Public Welfare Technology Application Research Project(LGC20E010002)National Natural Science Foundation of China(51877094)。
文摘The microstructure of twinning as well as the phase boundary between 1:5 H and 2:17 R phase in Fe-rich Sm_(2)Co_(17)-type magnets was characterized at atomic scale using nanobeam diffraction and highresolution STEM-HAADF imaging,and the reason for the dramatic increase of coercivity during slow cooling was investigated based on the microchemistry analysis.The twinning relationship in the 2:17 R phase originates from ordered substitution of Sm atoms by Co-Co atomic pairs on every three(3033)and(3033)planes,leading to formation of two corresponding equivalent twin variants.The basal plane of the 2:17 R phase,the 1:3 R platelet phase across the 2:17 R cell and the 1:5 H cell boundary phase between two adjacent 2:17 R cells all can act as effective twin boundary.The cell boundary phase is precipitated along the pyramidal habit plane,and a fully coherent phase boundary(PB)is formed between the 1:5 H and 2:17 R phases with the orientation relationship to be PB//(1121)1:5 H//(1011)_(2):17 R.The phase boundary may either be parallel to or intersect with the pyramidal planes occupied by Co-Co atomic pairs.The substantial increase of coercivity during slow cooling is ascribed to the development of large gradient of the elements concentration within the cell boundary phase,resulting in large gradient of domain wall energy,and thus the pinning strength of the cell boundary phase against magnetic domain wall motion is significantly enhanced.
基金Project supported by the National Natural Science Foundation of China(51871063,51771055)。
文摘The as-solution-treated Sm_(2)Co_(17)-type magnets exhibiting a single 1:7 H phase with different average grain sizes(D) were designed.Anisotropy of bending strength(R_(bb))and compressive strength(R_(mc)) of the magnets were investigated.Moreover,the R_(bb) increases from 86 to 173 MPa with D decreasing from~52 to~18 μm for group c//h samples.The Hall-Petch correlation was employed to reveal the effect of grain size on mechanical properties of the magnets,giving deep understanding of the mechanical anisotropy characteristics.The relatively high Hall-Petch coefficient K^(Rbb)(0.79 MPa·m^(1/2)) gives rise to the largest R_(bb)(173 MPa) for group c//h samples.The mechanical anisotropy of the samples is well explained based on crystal structure and grain size features(grain boundaries).Grain refinement is an effective way to enhance the mechanical properties of Sm_(2)Co_(17)-type sintered magnets.
基金financially supported by the National Key Research and Development Program of China(No.2016YFB0700903)the National Natural Science Foundation of China(Nos.51871063 and 51590882)。
文摘It is confirmed that the solid solution temperature range to obtain optimal magnetic properties is different for the magnets with different Fe contents,and the correlation between magnetic properties and microstructures influenced by solid solution temperature(Ts)has been systematically studied.The optimal solid solution temperature range is 1413-1463 K for the Sm(Co_(bal)Fe_(0.213)Cu_(0.073)Zr_(0.024))_(7.6)magnet,which is higher than that of the Sm(Co_(bal)Fe_(0.262)Cu_(0.073)Zr_(0.024))_(7.6)magnet(1403-1453 K),and the optimal T_s range is about 50 K for both of the magnets.The solid solution temperature range shifting toward relatively high temperature is due to the increase in a phase transition temperature.The magnet solution-treated at proper temperature exhibits 1:7 H single phase,and intact cell structure and high Cu concentration(23.12 at%)in the cell boundary are found after aging process,which makes the magnet shows high intrinsic coercivity(H_(cj))and magnetic field at knee-point(H_(knee)).At a lower solid solution temperature,the 2:17 H,1:5 H and Zr-rich precipitation phases appear,which affects the cell structure,density of lamellar phase and Cu concentration in the cell boundary,leading to the reduced magnetic properties.However,at a higher solid solution temperature,there exist obviously light gray and dark regions with different Sm,Cu and Fe contents in scanning electron microscopy observation,and the magnet shows low pinning field in the two regions and incomplete cell structure,resulting in an inferior H_(cj)and H_(knee).
