Effect of yttrium substitution on magnetic properties and service performances of Nd-Fe-B sintered magnets

We successfully fabricated partial Y substituted NdY-Fe-B magnets with nominal compositions of(Nd_(1-x)Y_(x))_(13.80)Fe_(ba1)Al_(0.24)Cu_(0.1)B_(6.04)(at%,x=0,0.1,0.2,0.3,0.4) by powder metallurgy process and the magnetic properties as well as service performances of the magnets were also systematically investigated.The phase constituents of the magnets have no obvious variation within the whole range of Y content,while the main phase grains form in-situ core-shell structure where Y gathers in the core and Nd mainly distributes in the shell.Compared with pure Nd-Fe-B magnets,the magnetic performances of Y substituted magnets slightly decrease on account of the poor intrinsic magnetic properties of Y_(2)Fe_(14)B.Fortunately,the μ_(O)M_(r),μ_(O)H_(cj) and(BH)_(max) of the 20 at% Y magnet still remain at a high level of 1.325 kG,1.173 kOe and 342.884 kj/m^(3),which approaches the performances of commercial N45-grade magnet.The service performances of Y substituted magnets indicate that though the surface corrosion products and Vickers hardness of the NdY-Fe-B magnets increase to a certain extent compared to Nd-Fe-B,the magnets with Y substitution still display relatively good service performances.Therefore,on the basis of sacrificing little partial magnetic and service performances,Y substituted Nd can still prepare NdY-Fe-B medium-grade magnets.By this way,we achieve the balanced utilization of rare earth resources,which has significant meanings for the industry and scientific research.

Effects of Nd-Ga intergranular addition on microstructure and magnetic properties of heavy-rare-earth-free Nd-Fe-B sintered magnets

In this study,we propose an approach of grain boundary modification that can significantly increase the coercivity of the B-lean Nd-Fe-B sintered magnets by intergranular addition of Nd-Ga.The coercivity is substantially enhanced from 1.51 to 2.04 T through optimizing the microstructure and adjusting the phase composition for the grain boundary phase in the annealed magnets.The matrix grains are covered by a continuous thin grain boundary phase accompanying the formation of intermetallic Nd_(6)Fe_(13)Ga phases.The analysis of magnetic behaviors above Curie temperature confirms that the grain boundary phase of annealed Nd-Ga doped magnets appears to be non-ferromagnetic,facilitating the intergrain exchange decoupling.Microstructure observation in grain boundary area indicates that some surface of the matrix grain is dissolved in the formation process of the Nd_(6)Fe_(13)Ga phase.It gives rise to a decrease in the proportion of matrix grains and saturation magnetization of the magnet.The detailed relationship between magnetic properties and microstructure is discussed based on these results.

A comparative study of NdY-Fe-B magnet and NdCe-Fe-B magnet

Low cost and high abundance rare earth elements Y and Ce have attracted tremendous interests of the industrial and scientific societies for fabricating the highly cost-performance efficient rare earth permanent magnets.However,the effect of separate replacement of Nd by Y or Ce on the performances of NdFeB-type magnet under the same atomic ratio and preparation conditions is still unclear.In this work,we systematically investigated the magnetic properties,thermal stabilities and service performances of(Nd_(0.8)Y_(0.2))_(13.80)Fe_(bal)Al_(0.24)Cu_(0.1)B_(6.04)(atomic fraction,denoted as 20 Y)and(Nd_(0.8)Ce_(0.2))_(13.80)Fe_(bal)Al_(0.24)Cu_(0.1)B_(6.04)(atomic fraction,denoted as 20 Ce)magnets.The results demonstrate that theμ_(0)M_(r),μ_(0)H_(c)and(BH)_(max)of 20 Y magnet are respectively 1.325 T,1.173 T and 343.467 kJ/m^(3),which are comprehensively higher than those of 20 Ce magnet(μ_(0)M_(r)=1.310 T,μ_(0)H_(c)=0.948 T,(BH)_(max)=321.105 kJ/m^(3)).Moreover,the 20 Y magnet has higher thermal stability compared with 20 Ce magnet which is favorable for the magnetic performances at elevated temperatures.The investigation of micro structure and elemental distribution indicates that the excellent magnetic performance s of NdY-Fe-B magnet can be attributed not only to the preferable intrinsic properties4πM_(s),H_(s)and T_(c)of Y_(2)Fe_(14)B,but also to the in-situ co re-shell structure of the 2:14:1 matrix phase grain with Yrich core and Nd-rich shell,along with the thicker grain boundary layer between the adjacent matrix phase grains in NdY-Fe-B magnet.Furthermore,the 20 Y magnet exhibits better mechanical property and higher corrosion resistance than 20 Ce magnet,which are helpful for prolonging the service life of the magnet in practical application.

Influence of Pr-Al-Co alloy diffusion source on magnetic properties and microstructure of sintered Nd-Fe-B magnets processed by grain boundary diffusion

In this study,the influence of the content of Al and Co in the diffusion source on the magnetic performance and microstructure of the diffused magnet was studied by grain boundary diffusion treatment with Pr_(70)Al_(30-x)Co_(x)(x=0 at%,10 at%,15 at%,20 at%,30 at%)alloys.When the Co content in the diffusion source increases from 0 at%to 10 at%,the coercivity enhancement in the Pr_(70)Al_(20)Co_(10)diffused magnet is the highest,increased from 1.62 to 2.24 T,higher than 2.01 T of the Pr_(70)Al_(30)diffused magnet.With further increase of Co content in the diffused source,the coercivity of the diffused magnet decreases gradually,the coercivity of Pr_(70)Al_(15)Co_(15),Pr_(70)Al_(20)Co_(10)and Pr_(70)Co_(30)diffused magnet is 2.15,1.99 and1.81 T,respectively.Microstructural analysis shows that plenty of continuous grain boundary phases(CGBPs)can be formed in the Pr_(70)Al_(20)Co_(10)diffused magnet under the synergistic effect of Al and Co,which leads to the enhancement of magnetic isolation between more adjacent grains.However,the amount of CGBP in the diffused magnets gradually decreases with the further increase of Co content in the diffusion source.

Effects of Pr-Cu-Ti intergranular addition on microstructure and magnetic properties of heavy-rare-earth-free Nd-Fe-B sintered magnets

By intergranular addition of Pr-Cu-Ti alloy powders in the Nd-Fe-B sintered magnets with the normal B component,we propose an approach to the optimization of grain boundary and local Nd-Fe-B composition system.The coercivity is enhanced from 1.42 to 1.86 T,while further addition leads to a reduction in remanence and coercivity.The analyses of phase composition reveal that Ti mainly exists in the form of metallic Ti alloy,and part of Ti combines with B to form the TiB2 phase after the liquid phase sintering process.This process results in a consumption of B in the local Nd-Fe-B composition system and a change of the grain boundary component,which contributes to the formation process of the RE_(6)(Fe,M)_(14) phase after the annealing process.Therefore,with the modification of grain boundary and composition system,the intergranular addition of Pr-Cu-Ti induces the generation of continuous thin grain boundary phases.It promotes the intergrain exchange decoupling,increasing the coercivity in the annealed magnet.While the excess addition results in the segregation of TiB_(2),as well as the precipitation of TiB_(2) into the Nd-Fe-B phase,which leads to structural defects.Thus,the further effort for the addition alloy with Ti to reduce the deterioration of the microstructure will lead to further improvement in magnetic properties.