The thermal expansion behavior of sintered Nd–Fe–B magnets is a crucial parameter for production and application.However, this aspect has not been thoroughly investigated. In this study, three different sintered Nd...The thermal expansion behavior of sintered Nd–Fe–B magnets is a crucial parameter for production and application.However, this aspect has not been thoroughly investigated. In this study, three different sintered Nd–Fe–B magnets with varying Co content(Co = 0, 6, 12 wt%) were prepared using the conventional powder metallurgy method, and four magnets oriented under different magnetic fields were prepared to compare. The thermal expansion behavior for the magnets was investigated using a linear thermal dilatometry in the temperature range of 20℃–500℃. It was found that, the coefficient of thermal expansion(CTE) increases with the increase of Co contents, while the anisotropy of thermal expansion decreases.The introduction of Co leads to continuous changes from negative to positive thermal expansion in the vertically oriented direction, which is important for the development of zero thermal expansion magnets. The thermal expansion of nonoriented magnets was found to be isotropic. Additionally, the anisotropy of thermal expansion increases with the increase of orientation degree. These results have important implications for the development of sintered Nd–Fe–B with controllable CTE.展开更多
A grain boundary diffusion(GBD)process with Pr_(80-x)Al_(x)Cu_(20)(x=0,10,15,20)low melting point alloys was applied to commercial 42M sintered Nd–Fe–B magnets.The best coercivity enhancement of a diffused magnet wa...A grain boundary diffusion(GBD)process with Pr_(80-x)Al_(x)Cu_(20)(x=0,10,15,20)low melting point alloys was applied to commercial 42M sintered Nd–Fe–B magnets.The best coercivity enhancement of a diffused magnet was for the Pr_(65)Al_(15)Cu_(20)GBD magnet,from 16.38 kOe to 22.38 kOe.Microstructural investigations indicated that increase in the Al content in the diffusion source can form a continuous grain boundary(GB)phase,optimizing the microstructure to enhance the coercivity.The coercivity enhancement is mainly due to the formation of a continuous GB phase to separate the main phase grains.Exchange decoupling between the adjacent main phase grains is enhanced after the GBD process.Meanwhile,the introduction of Al can effectively promote the infiltration of Pr into the magnet,which increases the diffusion rate of rare-earth elements within a certain range.This work provides a feasible method to enhance coercivity and reduce the use of rare-earth resources by partial replacement of rare-earth elements with non-rare-earth elements in the diffusion source.展开更多
As the channel for grain boundary diffusion(GBD)in Nd–Fe–B magnets,grain boundary(GB)phases have a very important effect on GBD.As doping elements that are commonly used to regulate the GB phases in Nd–Fe–B sinter...As the channel for grain boundary diffusion(GBD)in Nd–Fe–B magnets,grain boundary(GB)phases have a very important effect on GBD.As doping elements that are commonly used to regulate the GB phases in Nd–Fe–B sintered magnets,the influences of Ga and Zr on GBD were investigated in this work.The results show that the Zr-doped magnet has the highest coercivity increment(7.97 kOe)by GBD,which is almost twice that of the Ga-doped magnet(4.32 kOe)and the magnet without Ga and Zr(3.24 kOe).Microstructure analysis shows that ZrB_(2)formed in the Zr-doped magnet plays a key role in increasing the diffusion depth.A continuous diffusion channel in the magnet can form because of the presence of ZrB_(2).ZrB_(2)can also increase the defect concentration in GB phases,which can facilitate GBD.Although Ga can also improve the diffusion depth,its effect is not very obvious.The micromagnetic simulation based on the experimental results also proves that the distribution of Tb in the Zr-doped magnet after GBD is beneficial to coercivity.This study reveals that the doping elements Ga and Zr in Nd–Fe–B play an important role in GBD,and could provide a new perspective for researchers to improve the effects of GBD.展开更多
基金the National Key Research and Development Program of China (Grant No. 2021YFB3502900)the National Natural Science Foundation of China (Grant No. 51871063)+1 种基金the Key Technology Research and Development Program of Shandong Province, China (Grant No. 2019JZZY020210)the Major Projects in Inner Mongolia Autonomous Region, China。
文摘The thermal expansion behavior of sintered Nd–Fe–B magnets is a crucial parameter for production and application.However, this aspect has not been thoroughly investigated. In this study, three different sintered Nd–Fe–B magnets with varying Co content(Co = 0, 6, 12 wt%) were prepared using the conventional powder metallurgy method, and four magnets oriented under different magnetic fields were prepared to compare. The thermal expansion behavior for the magnets was investigated using a linear thermal dilatometry in the temperature range of 20℃–500℃. It was found that, the coefficient of thermal expansion(CTE) increases with the increase of Co contents, while the anisotropy of thermal expansion decreases.The introduction of Co leads to continuous changes from negative to positive thermal expansion in the vertically oriented direction, which is important for the development of zero thermal expansion magnets. The thermal expansion of nonoriented magnets was found to be isotropic. Additionally, the anisotropy of thermal expansion increases with the increase of orientation degree. These results have important implications for the development of sintered Nd–Fe–B with controllable CTE.
基金Project supported by the National Key Research and Development Program of China (Grant No.2021YFB3502802)Major Science and Technology Research and Development Project of Jiangxi Province,China (Grant No.20203ABC28W006)+2 种基金the Key Research and Development Program of Shandong Province,China (Grant No.2019JZZY010321)Major Project of“Science and Technology Innovation 2025”in Ningbo City (Grant No.2020Z046)the K.C.Wong Magna Fund in Ningbo University。
文摘A grain boundary diffusion(GBD)process with Pr_(80-x)Al_(x)Cu_(20)(x=0,10,15,20)low melting point alloys was applied to commercial 42M sintered Nd–Fe–B magnets.The best coercivity enhancement of a diffused magnet was for the Pr_(65)Al_(15)Cu_(20)GBD magnet,from 16.38 kOe to 22.38 kOe.Microstructural investigations indicated that increase in the Al content in the diffusion source can form a continuous grain boundary(GB)phase,optimizing the microstructure to enhance the coercivity.The coercivity enhancement is mainly due to the formation of a continuous GB phase to separate the main phase grains.Exchange decoupling between the adjacent main phase grains is enhanced after the GBD process.Meanwhile,the introduction of Al can effectively promote the infiltration of Pr into the magnet,which increases the diffusion rate of rare-earth elements within a certain range.This work provides a feasible method to enhance coercivity and reduce the use of rare-earth resources by partial replacement of rare-earth elements with non-rare-earth elements in the diffusion source.
基金Project supported by the National Natural Science Foundation of China(Grant No.52261037)self-deployed Projects of Ganjiang Innovation Academy,Chinese Academy of Sciences(Grant No.E055B002)+2 种基金the Project of Baotou City Science and Technology(Grant No.XM2022BT04)the Key Research Program of the Chinese Academy of Sciences(Grant No.ZDRW-CN-2021-3)the Key Research Project of Jiangxi Province(Grant No.20203ABC28W006)。
文摘As the channel for grain boundary diffusion(GBD)in Nd–Fe–B magnets,grain boundary(GB)phases have a very important effect on GBD.As doping elements that are commonly used to regulate the GB phases in Nd–Fe–B sintered magnets,the influences of Ga and Zr on GBD were investigated in this work.The results show that the Zr-doped magnet has the highest coercivity increment(7.97 kOe)by GBD,which is almost twice that of the Ga-doped magnet(4.32 kOe)and the magnet without Ga and Zr(3.24 kOe).Microstructure analysis shows that ZrB_(2)formed in the Zr-doped magnet plays a key role in increasing the diffusion depth.A continuous diffusion channel in the magnet can form because of the presence of ZrB_(2).ZrB_(2)can also increase the defect concentration in GB phases,which can facilitate GBD.Although Ga can also improve the diffusion depth,its effect is not very obvious.The micromagnetic simulation based on the experimental results also proves that the distribution of Tb in the Zr-doped magnet after GBD is beneficial to coercivity.This study reveals that the doping elements Ga and Zr in Nd–Fe–B play an important role in GBD,and could provide a new perspective for researchers to improve the effects of GBD.
基金Supported by China-Australia Government Special Found for Science and Technology Cooperation(CH060072)International Cooperation Program of the Science&Technology Committee of Shanghai Municipality(075207036)Program for Changjiang Scholars and Innovative Research Team in University(IRT0739)
