It is well known that Tb substitution for(Pr,Nd)in(Pr,Nd)-Fe-B based sintered magnetic materials is an effective way to increase intrinsic coercivity,but it is not quite clear whether the increment depends on the diff...It is well known that Tb substitution for(Pr,Nd)in(Pr,Nd)-Fe-B based sintered magnetic materials is an effective way to increase intrinsic coercivity,but it is not quite clear whether the increment depends on the different matrix phases with various doping ingredient or not,which is essential to develop high quality magnets with high coercivity more efficiently and effectively with economic consumption of expensive Tb and other costly heavy rare earths.In this paper,we investigated the efficiency of Tb substitution for magnetic property in(Pr,Nd)-Fe-B sintered permanent magnets by co-doping Ga and Cu elements.It is shown that Ga and Cu co-doping can effectively improve the efficiency of Tb substitution to increase the thermal stability and the coercivity.The intrinsic coercivity increases up to 549 and 987 kA/m respectively by 1.5 wt%and 3.0 wt%Tb substitution in Ga and Cu co-doped magnets while the intrinsic coercivity increases up to only 334 and 613 kA/m respectively by the same amounts of Tb substitution in non-Ga and low-Cu magnets.In other words,it demonstrates that there is about 329-366 kA/m linear equivalent enhancement of intrinsic coercivity by 1.0 wt%Tb substitution for(Pr,Nd)in Ga and Cu co-doped magnets.The temperature coefficients of both intrinsic coercivityβand remanenceαat 20-150℃by 3.0 wt%Tb substitution for the magnets with Ga and Cu co-doping are-0.47%/K and-0.109%/K respectively,and in contrast those values are-0.52%/K and 0.116%/K respectively for the non-Ga and low-Cu magnets.It is the principal reason for more efficient enhancement of magnetic property by Tb substitution in the Ga and Cu co-doped magnets in which Tb atoms are expelled from triple junction phases(TJPs)to penetrate into the grain boundary phases(GB phases)and thus modify the grain boundary.It is prospected that the efficiency of Tb substitution would rely on different matrix phases with various doping constituents.展开更多
The(Nd,Ce)-Fe-B sintered magnets were prepared by a dual-main-phase(DMP)process under the same conditions using different combinations of Nd-Fe-B with Ce-Fe-B and(Nd,Ce)-Fe-B strips.The crystalline and magnetic micros...The(Nd,Ce)-Fe-B sintered magnets were prepared by a dual-main-phase(DMP)process under the same conditions using different combinations of Nd-Fe-B with Ce-Fe-B and(Nd,Ce)-Fe-B strips.The crystalline and magnetic microstructures of DMP(Nd,Ce)-Fe-B magnets with the remanence of 11.92-12.68 kGs,the intrinsic coercivity of 3.97-5.31 kOe,and the maximum energy product of 23.08-32.99 MGOe have been investigated.Magnetic force microscope(MFM)investigations reveal that the DMP(Nd,Ce)-Fe-B magnets show maze-like patterns,which are like that of standard anisotropy Nd-Fe-B sintered magnets by and large.However,much finer domain structures mixing with coarse ones can be observed obviously in DMP(Nd,Ce)-Fe-B sintered magnets.The size distribution of the domain width of the DMP(Nd,Ce)-Fe-B magnet is not uniform obviously.The average domain width is W=0.912μm,and the fine domain width has only 0.216μm.The smaller domain width and more branch domain patterns exist in poorer coercivity DMP magnets.This is caused by the non-uniform Ce composition of poorer property DMP magnets and the grain boundary microstructure that is not conducive to improving the coercivity.Furthermore,it is found that some domains of rare-earth-rich grain boundary phases exhibit the characteristics of plate-like patterns rather than no-contrast by using MFM,indicating their ferromagnetism.Obvious correlations between the crystalline microstructure,chemical composition of phases,and magnetic structure were demonstrated for the DMP magnets.展开更多
To satisfy the application of different environments,grain boundary doping is commonly used in the preparation of sintered magnets to improve the coercivity and the corrosion resistance.In this paper,the alloys were p...To satisfy the application of different environments,grain boundary doping is commonly used in the preparation of sintered magnets to improve the coercivity and the corrosion resistance.In this paper,the alloys were prepared by mixing different ratios of the master alloy(Ce,Pr,Nd)-Fe-B and the sintering aid(Pr,Nd)-Al.The coercivity of sintered(Ce,Pr,Nd)-Fe-B magnet is substantially enhanced by doping 2 wt%of(Pr,Nd)-Al,while the maximum energy product decreases slightly.We systematically investigated the corrosion behavior and micro structure of the sintered magnets in order to determine the mechanism of the degradation.The sintered(Ce,Pr,Nd)-Fe-B magnets with 2 wt% of(Pr,Nd)-Al addition exhibit the decreasing corrosion rate compared with others,due to the distribution of intergranular phases.The electrode potential difference between the main phase and the RE-rich phase is reduced by the addition of Al,improving the potential and stability of RE-rich phase due to the higher electrode potential of Al than that of Nd,Pr or Ce.In addition,the element distribution of the magnets doped by(Pr,Nd)-Al indicates that the Al-rich shell formed at the marginal area of the Ce-rich phase improves its stability.Therefo re,intergranular adding te rnary(Pr,Nd)-Al alloy powders results in both high coe rcivity and good corrosion resistance synchronously.展开更多
Phase constituents,microstructures and magnetic properties of melt-spun Nd12-xYxFe81B6 Nb ribbons were investigated systematically.The influence of Y substitution for Nd on the phase stability,grain size and magnetic ...Phase constituents,microstructures and magnetic properties of melt-spun Nd12-xYxFe81B6 Nb ribbons were investigated systematically.The influence of Y substitution for Nd on the phase stability,grain size and magnetic exchange coupling was analyzed.It is found that all the ribbons crystallize in the tetragonal 2:14:1 structure,i.e.,with single hard magnetic phase at the roll speed of25 m s-1.With the increase in Y doping,Curie temperature(Tc)increases,while the coercivity decreases monoclinic ally.However,remanence magnetization(Br)and maximum energy product((BH)max)fluctuate and the maximum value is obtained at certain amount of Y.The optimum magnetic properties of intrinsic coercivity of intrinsic coercivity(Hcj)=908.2 kA·m-1 and(BH)max=118.52 kJ·m-3 are achieved when x=1.0.It can be attributed to the strengthened exchange coupling between the neighboring nanograins in Nd-Y-Fe-B meltspun powder based on the Henkel curves.Furthermore,Y substitution also significantly improves the temperature stability of magnetic performance.The coercivity temperature coefficient ofβ=-0.157%·℃-1 and remanence temperature coefficient ofα=-0.32%·℃-1 are gained,which are greatly reduced compared with those of the undoped Nd-Fe-B compounds.展开更多
Sintered(Ce,Nd)-Fe-B magnets with high cost performance were prepared by substituting of Ce for Nd with the dual-main phase method.The corrosion behaviors of dual-main phase sintered(CexNd1-x)30Fe69B1(x=0.15 wt%,0.3 w...Sintered(Ce,Nd)-Fe-B magnets with high cost performance were prepared by substituting of Ce for Nd with the dual-main phase method.The corrosion behaviors of dual-main phase sintered(CexNd1-x)30Fe69B1(x=0.15 wt%,0.3 wt%) magnets,which were named as Ce15 and Ce30,were studied in 3.5 wt% NaCl,6.6 wt% Na2 SO4 and 3.0 wt% NaOH aqueous solutions,respectively.The galvanic corrosion of Ce30 is stronger than that of Ce15.However,the mass loss value of Ce30 is smaller than Ce15 after free corrosion for 33 d in NaCl solution.In the other two solutions,all the results show that the corrosion resistance of Ce30 is better than that of Ce15.The scanning electron microscope results show that the crack and shedding of the magnetic phase of Ce30 is less than that of Ce15.Combined above,the abnormal corrosion behavior shows that Ce30 magnets perform better corrosion resistance than Ce15,and the degradation degree of magnetic phase mainly affects the corrosion resistance of magnets.展开更多
基金Project supported by the National Natural Science Foundation of China(51901089,52061015)Young Elite Scientists Sponsorship Program by CAST(YESS20200250)+3 种基金Young Talents Program of Jiangxi Provincial Major Discipline Academic and Technical Leaders Training Program(20212BCJ23008)China Postdoctoral Science Foundation(2020M682064)Postdoctoral Science foundation of Jiangxi Province(2020KY19)Technology Program of Fujian Province(2020H6201,2021T3063)。
文摘It is well known that Tb substitution for(Pr,Nd)in(Pr,Nd)-Fe-B based sintered magnetic materials is an effective way to increase intrinsic coercivity,but it is not quite clear whether the increment depends on the different matrix phases with various doping ingredient or not,which is essential to develop high quality magnets with high coercivity more efficiently and effectively with economic consumption of expensive Tb and other costly heavy rare earths.In this paper,we investigated the efficiency of Tb substitution for magnetic property in(Pr,Nd)-Fe-B sintered permanent magnets by co-doping Ga and Cu elements.It is shown that Ga and Cu co-doping can effectively improve the efficiency of Tb substitution to increase the thermal stability and the coercivity.The intrinsic coercivity increases up to 549 and 987 kA/m respectively by 1.5 wt%and 3.0 wt%Tb substitution in Ga and Cu co-doped magnets while the intrinsic coercivity increases up to only 334 and 613 kA/m respectively by the same amounts of Tb substitution in non-Ga and low-Cu magnets.In other words,it demonstrates that there is about 329-366 kA/m linear equivalent enhancement of intrinsic coercivity by 1.0 wt%Tb substitution for(Pr,Nd)in Ga and Cu co-doped magnets.The temperature coefficients of both intrinsic coercivityβand remanenceαat 20-150℃by 3.0 wt%Tb substitution for the magnets with Ga and Cu co-doping are-0.47%/K and-0.109%/K respectively,and in contrast those values are-0.52%/K and 0.116%/K respectively for the non-Ga and low-Cu magnets.It is the principal reason for more efficient enhancement of magnetic property by Tb substitution in the Ga and Cu co-doped magnets in which Tb atoms are expelled from triple junction phases(TJPs)to penetrate into the grain boundary phases(GB phases)and thus modify the grain boundary.It is prospected that the efficiency of Tb substitution would rely on different matrix phases with various doping constituents.
基金supported by the National Key Research and Development Program of China(Grant Nos.2021YFB3503003 and 2021YFB3503101)the National Natural Science Foundation of China(Grant No.51871063).
文摘The(Nd,Ce)-Fe-B sintered magnets were prepared by a dual-main-phase(DMP)process under the same conditions using different combinations of Nd-Fe-B with Ce-Fe-B and(Nd,Ce)-Fe-B strips.The crystalline and magnetic microstructures of DMP(Nd,Ce)-Fe-B magnets with the remanence of 11.92-12.68 kGs,the intrinsic coercivity of 3.97-5.31 kOe,and the maximum energy product of 23.08-32.99 MGOe have been investigated.Magnetic force microscope(MFM)investigations reveal that the DMP(Nd,Ce)-Fe-B magnets show maze-like patterns,which are like that of standard anisotropy Nd-Fe-B sintered magnets by and large.However,much finer domain structures mixing with coarse ones can be observed obviously in DMP(Nd,Ce)-Fe-B sintered magnets.The size distribution of the domain width of the DMP(Nd,Ce)-Fe-B magnet is not uniform obviously.The average domain width is W=0.912μm,and the fine domain width has only 0.216μm.The smaller domain width and more branch domain patterns exist in poorer coercivity DMP magnets.This is caused by the non-uniform Ce composition of poorer property DMP magnets and the grain boundary microstructure that is not conducive to improving the coercivity.Furthermore,it is found that some domains of rare-earth-rich grain boundary phases exhibit the characteristics of plate-like patterns rather than no-contrast by using MFM,indicating their ferromagnetism.Obvious correlations between the crystalline microstructure,chemical composition of phases,and magnetic structure were demonstrated for the DMP magnets.
基金the National Natural Science Foundation of China(51871063,51590882)the Open Projects of State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization。
文摘To satisfy the application of different environments,grain boundary doping is commonly used in the preparation of sintered magnets to improve the coercivity and the corrosion resistance.In this paper,the alloys were prepared by mixing different ratios of the master alloy(Ce,Pr,Nd)-Fe-B and the sintering aid(Pr,Nd)-Al.The coercivity of sintered(Ce,Pr,Nd)-Fe-B magnet is substantially enhanced by doping 2 wt%of(Pr,Nd)-Al,while the maximum energy product decreases slightly.We systematically investigated the corrosion behavior and micro structure of the sintered magnets in order to determine the mechanism of the degradation.The sintered(Ce,Pr,Nd)-Fe-B magnets with 2 wt% of(Pr,Nd)-Al addition exhibit the decreasing corrosion rate compared with others,due to the distribution of intergranular phases.The electrode potential difference between the main phase and the RE-rich phase is reduced by the addition of Al,improving the potential and stability of RE-rich phase due to the higher electrode potential of Al than that of Nd,Pr or Ce.In addition,the element distribution of the magnets doped by(Pr,Nd)-Al indicates that the Al-rich shell formed at the marginal area of the Ce-rich phase improves its stability.Therefo re,intergranular adding te rnary(Pr,Nd)-Al alloy powders results in both high coe rcivity and good corrosion resistance synchronously.
基金financially supported by the National Key Research and Development Program(No.2016YFB0700902).
文摘Phase constituents,microstructures and magnetic properties of melt-spun Nd12-xYxFe81B6 Nb ribbons were investigated systematically.The influence of Y substitution for Nd on the phase stability,grain size and magnetic exchange coupling was analyzed.It is found that all the ribbons crystallize in the tetragonal 2:14:1 structure,i.e.,with single hard magnetic phase at the roll speed of25 m s-1.With the increase in Y doping,Curie temperature(Tc)increases,while the coercivity decreases monoclinic ally.However,remanence magnetization(Br)and maximum energy product((BH)max)fluctuate and the maximum value is obtained at certain amount of Y.The optimum magnetic properties of intrinsic coercivity of intrinsic coercivity(Hcj)=908.2 kA·m-1 and(BH)max=118.52 kJ·m-3 are achieved when x=1.0.It can be attributed to the strengthened exchange coupling between the neighboring nanograins in Nd-Y-Fe-B meltspun powder based on the Henkel curves.Furthermore,Y substitution also significantly improves the temperature stability of magnetic performance.The coercivity temperature coefficient ofβ=-0.157%·℃-1 and remanence temperature coefficient ofα=-0.32%·℃-1 are gained,which are greatly reduced compared with those of the undoped Nd-Fe-B compounds.
基金Project supported by the National Natural Science Foundation of China(51871063,51571064,51590882)。
文摘Sintered(Ce,Nd)-Fe-B magnets with high cost performance were prepared by substituting of Ce for Nd with the dual-main phase method.The corrosion behaviors of dual-main phase sintered(CexNd1-x)30Fe69B1(x=0.15 wt%,0.3 wt%) magnets,which were named as Ce15 and Ce30,were studied in 3.5 wt% NaCl,6.6 wt% Na2 SO4 and 3.0 wt% NaOH aqueous solutions,respectively.The galvanic corrosion of Ce30 is stronger than that of Ce15.However,the mass loss value of Ce30 is smaller than Ce15 after free corrosion for 33 d in NaCl solution.In the other two solutions,all the results show that the corrosion resistance of Ce30 is better than that of Ce15.The scanning electron microscope results show that the crack and shedding of the magnetic phase of Ce30 is less than that of Ce15.Combined above,the abnormal corrosion behavior shows that Ce30 magnets perform better corrosion resistance than Ce15,and the degradation degree of magnetic phase mainly affects the corrosion resistance of magnets.
