Due to its large magnetocrystalline anisotropy field and high Curie temperature,SmCo-based magnets are irreplaceable in high-temperature applications,The hot-deformed SmCo-based magnets are especially attractive for t...Due to its large magnetocrystalline anisotropy field and high Curie temperature,SmCo-based magnets are irreplaceable in high-temperature applications,The hot-deformed SmCo-based magnets are especially attractive for their excellent corrosion resistance,making them more suitable for harsh environments.However,it is still challenging for hot-deformed SmCo-based magnets to obtain high magnetization and high coercivity simultaneously.Therefore,it is necessary to analyze the relationship between its microstructure and magnetic properties and explore its magnetic hardening mechanism to guide the further improvement of magnetic properties.In this paper,the anisotropic heterostructure SmCo_(5)magnet was prepared by combining large height-reduction and introducing a nano-grained Smrich phase.Strong c-axis texture,(BH)m of 16.1 MGOe,and H_(ci)of 9.6 kOe were obtained via the heterostructure with SmCo_(5)micron-grain and Sm-rich nano-scale precipitates.The magnetic domain observation and technical magnetization analysis demonstrate that the coe rcivity mechanism is dominated by nucleation.The results also show that the smooth and Sm-rich precipitated grain boundary provides weak pinning effects.It provides a reference for the development of high-pe rformance nanocrystalline SmCo_(5)magnets.展开更多
Nanocomposite permanent magnets have ultra-high theoretical magnetic energy products,due to cou-pling of the soft/hard magnetic phases,inciting strict microstructural requirements.In this study,the microstructure evol...Nanocomposite permanent magnets have ultra-high theoretical magnetic energy products,due to cou-pling of the soft/hard magnetic phases,inciting strict microstructural requirements.In this study,the microstructure evolution,including the phase transition,morphological changes,and texture formation,of hot-deformed SmCo-based nanocomposites under thermal-stress-strain coupling was characterized to determine a possible strategy for achieving high performance.The SmCo_(5)/α-Fe nanocomposites precursor contained fine and dispersed Sm(Fe,Co)_(5)and Fe-Co grains and exhibited a two-stage phase transforma-tion accompanied by grain growth.In the early stage of deformation at relatively low temperature,the adjacent Sm(Co,Fe)5 and Fe-Co phase formed the Sm_(2)(Co,Fe)_(17)-H phase,which was stable only with small grain sizes.In the high-temperature deformation stage,the Sm_(2)(Co,Fe)_(17)-H phase transformed into the Sm_(2)(Co,Fe)_(17)-R phase with large grain sizes.In addition,the strong c-axis texture formed in the Sm(Co,Fe)_(5)phase but not in the Sm_(2)(Co,Fe)_(17)-R phase.Subsequently,the phase transition process and texture formation mechanism were systematically analyzed by transmission electron microscopy.The ini-tiation of a slip system and/or preferential grain growth explained the formation of texture under the action of uniform stress and strain and assisted by dispersed Sm-rich nanograins.The Sm_(2)(Co,Fe)_(17)-R grains with poor orientations and large grain sizes did not achieve magnetic hardening,which also dam-age the magnetic properties.According to the results of this work,we also presented a new strategy to prepare high-performance SmCo-based nanocomposites magnets.展开更多
In this article,the Sm_(2)Co_(7)/α-Fe nanocomposite magnets were prepared by high energy ball milling and spark plasma sintering method.The effect of soft phase content on the magnetic properties was studied.Up to 30...In this article,the Sm_(2)Co_(7)/α-Fe nanocomposite magnets were prepared by high energy ball milling and spark plasma sintering method.The effect of soft phase content on the magnetic properties was studied.Up to 30 wt% α-Fe was added into Sm_(2)Co_(7) matrix without the decrease of remanence.Optimal energy product(BH)max of 9.2 MGOe was obtained with 20 wt% α-Fe.TEM observation shows that the grain size of α-Fe is 20-50 nm which ensures a good coupling effect between soft and hard phase.One more thing needs to be mentioned is that there exists inter-diffusion between Sm-Co phase and α-Fe phase.Moreover,our results can also illustrate that the Sm_(2)Co_(7)/α-Fe nanocomposite magnets are able to acquire better magnetic properties than the SmCo_(5)/α-Fe magnets prepared by the same process due to the large domain width of Sm_(2)Co_(7) phase.展开更多
The hot-deformed(HD) Nd-Fe-B magnets show heterogeneous microstructure composed of coarse and fine grain regions. It is significant to fully understand the influence of this complex microstructure on the magnetization...The hot-deformed(HD) Nd-Fe-B magnets show heterogeneous microstructure composed of coarse and fine grain regions. It is significant to fully understand the influence of this complex microstructure on the magnetization reversal process which can give the guidance for the enhancement of the magnetic properties. In this paper, the heterogeneous microstructure of the(HD) Nd-Fe-B magnets were characterized from the morphology, size, macro-texture and micro-structure. In addition, the magnetization reversal process of the HD Nd-Fe-B magnets was systematically analyzed by magnetic measurement, insitu domain evolution observation and micromagnetic simulation. The results indicate that the HD NdFe-B magnets mainly consist of fine grain regions(FGRs) and coarse grain regions(CGRs). The FGRs show plate-like grains with fine grain size and strong c-axis texture, while the CGRs show equiaxial grains with large grain size and weak c-axis texture. In particular, it is worth noting that the texture in homogeneity exists not only between FGRs and CGRs, but also inside both the FGRs and CGRs. The dominant coercivity mechanism of the HD Nd-Fe-B magnets is domain wall pinning. Also, the experimental analysis shows that the reverse domain is formed and expanded in the CGRs at low reverse applied field, while the reverse domain occurs in the FGRs at higher reverse applied field. The micromagnetic simulation results also confirm the above magnetization reversal process. In addition, micromagnetic simulation results also show that the orientation of the grains also affects the pinning strength, besides the grain size.展开更多
In this paper, microstructure, micromagnetic structure, texture, together with magnetic properties of the hot-deformed(HD) Nd-Fe-B magnets were systematically studied to understand the deformation process and the form...In this paper, microstructure, micromagnetic structure, texture, together with magnetic properties of the hot-deformed(HD) Nd-Fe-B magnets were systematically studied to understand the deformation process and the formation mechanism of c-axis texture. The results show that the platelet grains are formed in the fine-grain regions at the initial stage of the deformation. As the amount of deformation increases, the proportion of platelet grains increases and arranges gradually, causing the formation of c-axis texture, till the grain merging occurres when the deformation is excessive. It should be noted that the rare earth-rich phase in the fine-grained region slowly diffuses to the coarse-grained region where only grain growth can be observed during deformation. The deformation mechanism and formation of c-axis texture in HD Nd-Fe-B magnets can be deduced to be accomplished by the processes of dissolution-precipitation diffusion, grain rotation and grain arrangement, based on the characterization of microstructure and texture evolution. Also, approaches to optimize the preparation process and magnetic properties of the hot-deformed Nd-Fe-B magnets were discussed.展开更多
基金Project supported by the National Key Research and Development Program of China(2021YFB3500300)the National Natural Science Foundation of China(51931007,51871005,52201212,52271161)+1 种基金General Program of Science and Technology Development Project of Beijing Municipal Education Commission of China(KM201710005006)the Program of Top Disciplines Construction in Beijing(PXM2019_014204_500031)。
文摘Due to its large magnetocrystalline anisotropy field and high Curie temperature,SmCo-based magnets are irreplaceable in high-temperature applications,The hot-deformed SmCo-based magnets are especially attractive for their excellent corrosion resistance,making them more suitable for harsh environments.However,it is still challenging for hot-deformed SmCo-based magnets to obtain high magnetization and high coercivity simultaneously.Therefore,it is necessary to analyze the relationship between its microstructure and magnetic properties and explore its magnetic hardening mechanism to guide the further improvement of magnetic properties.In this paper,the anisotropic heterostructure SmCo_(5)magnet was prepared by combining large height-reduction and introducing a nano-grained Smrich phase.Strong c-axis texture,(BH)m of 16.1 MGOe,and H_(ci)of 9.6 kOe were obtained via the heterostructure with SmCo_(5)micron-grain and Sm-rich nano-scale precipitates.The magnetic domain observation and technical magnetization analysis demonstrate that the coe rcivity mechanism is dominated by nucleation.The results also show that the smooth and Sm-rich precipitated grain boundary provides weak pinning effects.It provides a reference for the development of high-pe rformance nanocrystalline SmCo_(5)magnets.
基金This work was financially supported by the National Key R&D Program of China(No.2021YFB3500300)the National Natural Science Foundation of China(Nos.51931007,51871005,and 51801005)+2 种基金the Key Program of Science and Technology Development Project of Beijing Municipal Education Commission of China(No.KZ202010005009)the Chaoyang District Postdoctoral Research Foundation(No.2021ZZ-36)the International Research Cooperation Seed Fund of Beijing University of Technology(No.2021B23).
文摘Nanocomposite permanent magnets have ultra-high theoretical magnetic energy products,due to cou-pling of the soft/hard magnetic phases,inciting strict microstructural requirements.In this study,the microstructure evolution,including the phase transition,morphological changes,and texture formation,of hot-deformed SmCo-based nanocomposites under thermal-stress-strain coupling was characterized to determine a possible strategy for achieving high performance.The SmCo_(5)/α-Fe nanocomposites precursor contained fine and dispersed Sm(Fe,Co)_(5)and Fe-Co grains and exhibited a two-stage phase transforma-tion accompanied by grain growth.In the early stage of deformation at relatively low temperature,the adjacent Sm(Co,Fe)5 and Fe-Co phase formed the Sm_(2)(Co,Fe)_(17)-H phase,which was stable only with small grain sizes.In the high-temperature deformation stage,the Sm_(2)(Co,Fe)_(17)-H phase transformed into the Sm_(2)(Co,Fe)_(17)-R phase with large grain sizes.In addition,the strong c-axis texture formed in the Sm(Co,Fe)_(5)phase but not in the Sm_(2)(Co,Fe)_(17)-R phase.Subsequently,the phase transition process and texture formation mechanism were systematically analyzed by transmission electron microscopy.The ini-tiation of a slip system and/or preferential grain growth explained the formation of texture under the action of uniform stress and strain and assisted by dispersed Sm-rich nanograins.The Sm_(2)(Co,Fe)_(17)-R grains with poor orientations and large grain sizes did not achieve magnetic hardening,which also dam-age the magnetic properties.According to the results of this work,we also presented a new strategy to prepare high-performance SmCo-based nanocomposites magnets.
基金Project supported by the National Natural Science Foundation of China(51931007,51871005,51801005)。
文摘In this article,the Sm_(2)Co_(7)/α-Fe nanocomposite magnets were prepared by high energy ball milling and spark plasma sintering method.The effect of soft phase content on the magnetic properties was studied.Up to 30 wt% α-Fe was added into Sm_(2)Co_(7) matrix without the decrease of remanence.Optimal energy product(BH)max of 9.2 MGOe was obtained with 20 wt% α-Fe.TEM observation shows that the grain size of α-Fe is 20-50 nm which ensures a good coupling effect between soft and hard phase.One more thing needs to be mentioned is that there exists inter-diffusion between Sm-Co phase and α-Fe phase.Moreover,our results can also illustrate that the Sm_(2)Co_(7)/α-Fe nanocomposite magnets are able to acquire better magnetic properties than the SmCo_(5)/α-Fe magnets prepared by the same process due to the large domain width of Sm_(2)Co_(7) phase.
基金Project supported by the National Natural Science Foundation of China(51331003)the International S&T Cooperation Program of China(2015DFG52020)+2 种基金Foundation of Beijing Municipal Education Commission(KM201610005025)Beijing Postdoctoral Research Foundation(2018-ZZ-019)2018 Youth Foundation Project of College of Materials Science and Engineering of Beijing University of Technology(Advanced subject,PXM2019_014204_500031)
文摘The hot-deformed(HD) Nd-Fe-B magnets show heterogeneous microstructure composed of coarse and fine grain regions. It is significant to fully understand the influence of this complex microstructure on the magnetization reversal process which can give the guidance for the enhancement of the magnetic properties. In this paper, the heterogeneous microstructure of the(HD) Nd-Fe-B magnets were characterized from the morphology, size, macro-texture and micro-structure. In addition, the magnetization reversal process of the HD Nd-Fe-B magnets was systematically analyzed by magnetic measurement, insitu domain evolution observation and micromagnetic simulation. The results indicate that the HD NdFe-B magnets mainly consist of fine grain regions(FGRs) and coarse grain regions(CGRs). The FGRs show plate-like grains with fine grain size and strong c-axis texture, while the CGRs show equiaxial grains with large grain size and weak c-axis texture. In particular, it is worth noting that the texture in homogeneity exists not only between FGRs and CGRs, but also inside both the FGRs and CGRs. The dominant coercivity mechanism of the HD Nd-Fe-B magnets is domain wall pinning. Also, the experimental analysis shows that the reverse domain is formed and expanded in the CGRs at low reverse applied field, while the reverse domain occurs in the FGRs at higher reverse applied field. The micromagnetic simulation results also confirm the above magnetization reversal process. In addition, micromagnetic simulation results also show that the orientation of the grains also affects the pinning strength, besides the grain size.
基金supported by the Beijing Natural Science Foundation under Grant(2202005)the Natural Science Foundation of China(No.51331003,No.51931007)+2 种基金the General Program of Science and Technology Development Project of Beijing Municipal Education Commission of China under Grant(KM201710005006)the International S&T Cooperation Program of China under Grant2015DFG52020the Program of Top Disciplines Construction in Beijing under GrantPXM2019014204500031。
文摘In this paper, microstructure, micromagnetic structure, texture, together with magnetic properties of the hot-deformed(HD) Nd-Fe-B magnets were systematically studied to understand the deformation process and the formation mechanism of c-axis texture. The results show that the platelet grains are formed in the fine-grain regions at the initial stage of the deformation. As the amount of deformation increases, the proportion of platelet grains increases and arranges gradually, causing the formation of c-axis texture, till the grain merging occurres when the deformation is excessive. It should be noted that the rare earth-rich phase in the fine-grained region slowly diffuses to the coarse-grained region where only grain growth can be observed during deformation. The deformation mechanism and formation of c-axis texture in HD Nd-Fe-B magnets can be deduced to be accomplished by the processes of dissolution-precipitation diffusion, grain rotation and grain arrangement, based on the characterization of microstructure and texture evolution. Also, approaches to optimize the preparation process and magnetic properties of the hot-deformed Nd-Fe-B magnets were discussed.
