烧结Nd25.5Dy6.5Co13FebalM1.05B0.98磁体温度稳定性和力学性能研究

本文采用速凝甩带-氢破-气流磨-取向成型-烧结回火等工序,同时添加Dy和Co元素,制备了烧结Nd_25.5Dy_6.5Co₁₃Fe_balM_1.05B_0.98磁体(Co13磁体),室温下磁能积(BH)_max=30.88 MGOe,矫顽力H_cj=19.01 kOe.与Nd₃₀Dy_1.5Co_0.5Fe_balM_1.05B_0.98(35SH)磁体相比, Co13磁体的室温磁性能略低,但温度稳定性显著提升,剩磁温度系数α从–0.136%/℃提升至–0.065%/℃(室温—180℃);居里温度T_C从310℃升高至约454℃;最高使用温度T_W从165℃提升到约200℃.力学性能测试和断口分析表明, Co13磁体中由于Co含量较高,主相晶粒发生解理断裂的比例提高...     

氧化物隔离对Si基片上生长L1_0相FePt薄膜磁性的影响

用MgO和SiO_2两种氧化物将FePt薄膜与Si(100)基片隔离,分析隔离层在FePt层发生A1→L1_0转变过程中的作用,寻找用Si母材涂敷L1_0-FePt磁性层来提高磁力显微镜针尖矫顽力的合理方案.采用磁控溅射法在400?C沉积Fe Pt薄膜,在不同温度进行2 h的真空热处理,分析晶体结构和磁性的变化.结果表明:没有隔离层,Si基片表层容易发生扩散,50 nm厚FePt薄膜的矫顽力最大只有5kOe(1 Oe=10~3/(4π)A·m~(-1));而插入隔离层,矫顽力可以超过10 kOe;MgO在Si基片上容易碎裂,热处理温度不能高于600?C,用作隔离层,FePt的最大矫顽力为12.4 kOe;SiO_2与Si基片的晶格匹配更好,热膨胀系数差较小,能承受的最高热处理温度可以超过800?C,使得Fe Pt的矫顽力可以在5 kOe到15 kOe范围内调控,更适合用于制作矫顽力高并可控的磁力显微镜针尖.     

稀土含量对速凝工艺制备(Nd,Dy)-(Fe,Al)-B合金结构和磁性能的影响

采用双合金法制备了不同稀土含量的(Nd,Dy)-(Fe,Al)-B合金系列,研究了稀土含量的多寡对薄带和最终烧结磁体的微观结构和磁性能的影响.研究结果表明,适量的稀土含量(～3145%)不仅能改善速凝带主相(Nd,Dy)₂Fe₁₄B的单相性,还有利于富稀土(Nd,Dy)相在晶界的均匀分布.当主相薄带的稀土含量在接近2∶14∶1相稀土含量时,磁体的内禀矫顽力和磁能积显著提高.当稀土含量较少时,对速凝薄带的合适时效热处理将能有效地提高最终烧结NdFeB磁体的磁特性. 关键词： 双相烧结 速凝技术 微观结构 磁性能     

添加Ag_2O对YBa_2Cu_3O_(7-δ)体材料显微结构与超导电性的影响 (Ⅱ)显微结构分析与Ag的作用机理探讨

本文研究了添加 Ag_2O 对 YBa_2Cu_3O_(7-δ)体材料显微结构的影响.实验结果表明:在(YBa_2Cu_3O_(7-δ))_(1-x)Ag_x 复合超导材料中,根据烧成温度的不同,显微结构存在显著差导.960℃以下烧成的试样,结构致密,超导晶粒细小而不规则,Ag 的分布较均匀;970～1000℃烧成的试样,结构更致密,其中存在许多超导晶粒择优取向的区域,并有细小的211相包裹物存在,试样中 Ag 偏聚成团状.本文认为在不同烧成温度下 Ag 的作用机理不同,在960℃以下烧成时,Ag 的主要作用是使晶粒细化,晶界金属化和试样致密化;而在高于970℃烧成时,Ag 的主要作用是净化晶界和导致晶粒有序排列区域及强钉扎中心——细小的211相包裹物的形成.     

Sm(Co,Cu,Fe,Zr)z反磁化过程的微磁学分析

通过微磁学有限元方法研究了微结构对各向异性的Sm(Co,Cu,Fe,Zr)z磁性能的影响， 并 对不同温度下的退磁曲线进行了计算.计算结果表明，矫顽力随着2∶17相晶粒尺寸的增大 而增大，随1∶5晶界相厚度的增大而减小；通过减小晶界相厚度或增大晶粒尺寸可以有效提 高 磁能积.反磁化的物理机制主要为形核机制，主要表现为首先在晶界相形成反磁化核，随 着 磁场的增大反磁化核不断长大，最后导致整个磁体的磁化反转；而当温度升高时，晶界相逐 渐变成非磁性相，使得反磁化核难以形成，因此出现了反常的矫顽力温度依赖关系. 关键词： 微磁学 有限元 微结构 磁性能     

MnBiDy(Sm)永磁膜的结构和磁性

报道了采用真空蒸镀的方法制备的MnBiDy(Sm)永磁膜的结构和磁性.Mn:Bi:Dy(Sm)的投料比为2:1:0.10.薄膜经过退出处理(350—425℃,保温4h)后,具有NiAs型hcp结构,C轴垂直膜面,剩余磁感应强度B=3.4-6.5kG,内禀矫顽力_MH_c≈3-8kOe,最大磁能积(BH)_(max)=13.39MG·Oe.实验发现,薄膜厚度对MnBiDy(Sm)永磁膜的结构和磁性具有很大的影响. 关键词：     

R_2(Fe_(1-x)Al_x)_(14)B的内禀磁性和永磁性能(R=Nd和Y)

本文研究了Al在R_2(Fe_(1-x)Al_x)_(14)B多元合金中的固溶度(R=Nd和Y),当x<0.1时,可形成四方结构。研究了在此类合金中,饱和磁化强度、居里温度、磁晶各向异性等内禀磁性,以及矫顽力和磁能积等永磁性能随Al含量的变化。发现以Al代换Fe时,使铁次点阵的磁晶各向异性出现极值;同时以Al代换Fe时,可使磁体的矫顽力显著提高。以Co和Al同时对Fe进行代换,制造成分约为Nd_(16·5)B_7(Fe_(1-x-y)Al_xCo_y)_(76.5)的磁体,既可提高居里温度,又可提高矫顽力,从而可以改善具有高磁能积磁体的温度性能和减少磁体的总损失。     

三元Co_(79)Zr_(18)Cr_3合金中高矫顽力

通过在Co_(82)Zr_(18)合金中添加过渡族元素Cr的方法,利用快淬工艺,制备出了Co_(82-x)Zr_(18)Cr_x(x=0,2,3,4)快淬合金薄带,利用磁性测量、X光衍射、热磁分析、扫描电子显微镜,对其磁性能、相组成、微结构进行了研究,实验结果表明,在Co_(82)Zr_(18)合金中添加少量的Cr可以使其矫顽力(iHc)显著提高,其中,Co_(79)Zr_(18)Cr_3快淬薄带经600℃退火处理后iHc=6.5 kOe.相分析发现,600℃退火后的Co_(79)Zr_(18)Cr_3快淬薄带由单一Co_(11)Zr_2相组成,Cr原子进入到了Co_(11)Zr_2相的晶格之中替换了原子半径相对较小的Co原子,这导致了Co_(11)Zr_2居里温度(T_C)的降低却使其磁晶各向异性场(Ha)显著提高;另一方面,通过微结构研究发现,未退火的Co_(79)Zr_(18)Cr_3快淬薄带由50—80 nm的等轴晶粒组成,经600℃退火后,其晶粒形态并未发生改变然而晶粒尺寸却增长到400—500nm。     

Ce_(0.8)Pr_(0.2-x)Nd_xO_(2-δ)(x=0.02,0.05,0.1)固溶体的合成与性质研究

采用溶胶-凝胶法制备了双稀土掺杂氧化铈Ce_(0.8)Pr_(0.2-x)Nd_xO_(2-δ)(x=0.02,0.05,0.1)固溶体。X射线衍射分析阐明,经800℃烧结的全部固溶体都形成了单相立方萤石结构,平均晶粒尺寸在20~25 nm之间。拉曼光谱结果阐明,固溶体Ce_(0.8)Pr_(0.2-x)Nd_xO_(2-δ)是具有氧空位的立方萤石结构,适量的掺杂Nd有利于Ce_(0.8)Pr_(0.2-x)Nd_xO_(2-δ)氧空位浓度的增加。阻抗谱结果阐明,稀土双掺杂的Ce_(0.8)Pr_(0.2-x)Nd_xO_(2-δ)比稀土单掺杂的Ce_(0.83)Sm_(0.17)O_(2-y)的电导率高,Ce_(0.8)Pr_(0.18)Nd_(0.02)O_(2-δ)的电导率最大,600℃时电导率为1.85×10~(-2)S/cm。     

晶粒易轴取向度对纳米晶永磁Pr2Fe14B磁性的影响

构造了立方和不规则形状晶粒的各向异性纳米晶单相Pr₂Fe₁₄B磁体 .利用微磁学的有限元法，模拟计算了样品的磁滞回线.计算结果表明，随着磁体晶粒易轴取向度的变差， 磁体的剩磁、矫顽力均随之下降.不同晶粒尺寸的纳米晶单相Pr₂Fe_{14B磁体，其磁 性能随取向度的变化快慢不同，原因在于磁体中的晶间交换作用 (IGEC) 的强弱不同.随着 晶粒取向度的提高，纳米晶单相磁体的矫顽力逐渐增加，这完全不同于烧结磁体. 关键词： 纳米晶磁体 矫顽力 剩磁}     

Coercivity enhancement of sintered Nd-Fe-B magnets by grain boundary diffusion with Pr80-xAlxCu20 alloys

A grain boundary diffusion (GBD) process with Pr_80-xAl_xCu₂₀ (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 Pr₆₅Al₁₅Cu₂₀ 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.     

Effects of post-sinter annealing on microstructure and magnetic properties of Nd–Fe–B sintered magnets with Nd–Ga intergranular addition

We investigate the effects of post-sinter annealing on the microstructure and magnetic properties in B-lean Nd–Fe–B sintered magnets with different quantities of Nd–Ga intergranular additions. The magnet with fewer Nd–Ga additions can enhance 0.2 T in coercivity, with its remanences nearly unchanged after annealing. With the further increase of the Nd–Ga addition, the annealing process leads coercivity to increase 0.4 T, accompanied by a slight decrease of remanence. With the Nd–Ga addition further increasing and after annealing, however, the increase of coercivity is basically constant and the change of remanence is reduced. Microstructure observation indicates that the matrix grains are covered by continuous thin grain boundary phase in the magnets with an appropriate Nd–Ga concentration after the annealing process. However, the exceeding Nd–Ga addition brings out notable segregation of grain boundary phase, and prior formation of part RE6 Fe13 Ga phase in the sintered magnet. This prior formation results in a weaker change of remanence after the annealing process.Therefore, the diverse changes of magnetic properties with different Nd–Ga concentrations are based on the respective evolution of grain boundary after the annealing process.     

Effect of post-sintering annealing on microstructure and coercivity of Al85Cu15-added Nd-Fe-B sintered magnets

Effects of post-sintering annealing on the microstructure and coercivity have been investigated for the Al₈₅Cu₁₅-added (Pr, Nd)_14.8Fe_78.7B_6.5 sintered magnets. It is found that the optimum annealing temperature at which the coercivity _iH_c reaches a maximum decreases from 550 °C for the magnets added with 0.3% and 0.6% Al₈₅Cu₁₅ to 480 °C for the magnets added with 0.9% and 1.2% Al₈₅Cu₁₅. The decrease in optimum annealing temperature is related to the precipitation of Al-Cu or (Pr, Nd)−Cu liquid phase among (Pr, Nd)-rich phases during annealing. Existence of Al-Cu or (Pr, Nd)−Cu liquid phase is beneficial to dissolve the irregularities of (Pr, Nd)₂Fe₁₄B grain interface and increase the quantities of (Pr, Nd)-rich phases at the grain boundary, thus optimizing the grain boundary microstructure. The modifications of the microstructure are helpful to decouple the exchange interaction between (Pr, Nd)₂Fe₁₄B hard magnetic grains, thereby increasing the coercivity.     

Magnetic properties and grain-boundary structure transition of melt-spun (Sm0.12Co0.87Cu0.01)97(VC)3 under annealing

Effects of annealing treatment on the magnetic properties and microstructure of SmCo₇-based magnets doped with VC and Cu were investigated. The coercivity of the as-spun ribbons (Sm_0.12Co_0.87Cu_0.01)₉₇(VC)₃ was 3.6 kOe. It was increased to 7.3 kOe after annealing at 800 °C for 15 min. A fixed single 1:7H structure and regular 1:7H dendrite grains with long axes preferentially parallel to each other had been attained during rapid solidification and subsequent annealing treatment. However, TEM results revealed that there was grain-boundary phase rich in C and Cu besides 1:7H phase in the as-solidified ribbon. After annealing, the grain-boundary phase decomposed to Cu-, Sm- and C-rich intergranular phases. Cu-, Sm- and C-rich regions formed at the grain boundaries after annealing improved the coercivity of (Sm_0.12Co_0.87Cu_0.01)₉₇(VC)₃ by decreasing the magnetostatic interactions and act as effective domain wall pinning sites.     

The origin of coercivity decrease in fine grained Nd-Fe-B sintered magnets

Microstructures of fine grained Nd-Fe-B sintered magnets that were produced by the pressless process were investigated to understand the origin of the sudden coercivity decrease below a certain grain size. The intrinsic coercivity is inversely proportional to ln D² with the highest coercivity of 17 kOe at D∼4.5 μm, below which the coercivity drops as the grain size decreases. We found that the degradation of the coercivity of the magnet with a grain size of 3 μm was mainly caused by the inhomogeneous distribution of fcc-Nd oxide whose volume fraction increased with respect to the dhcp Nd-rich phase.     

Improvement in coercivity,thermal stability,and corrosion resistance of sintered Nd-Fe-B magnets with Dy_(80)Ga_(20) intergranular addition

To investigate the coercivity,corrosion resistance,and thermal stability of Nd-Fe-B magnets,their properties were investigated at room and high temperature before and after doping with Dy_(80)Ga_(20)(at.%) powder.The coercivity of the magnets increased from the undoped value of 12.72 kOe to a doped value of 21.44 kOe.A micro-structural analysis indicates that a well-developed core-shell structure forms in the magnets doped with Dy_(80)Ga_(20) powder.The improvement in magnetic properties is believed to be related to the refined and uniform matrix grains,continuous grain boundaries,and a hardened(Nd,Dy)_2Fe_(14)B shell surrounding the matrix grains.Additionally,the doped magnets exhibit an obvious improvement in thermal stability.For the magnets with added Dy_(80)Ga_(20) powder,the temperature coefficients of remanence(α) and coercivity(β) increased to-0.106%℃~(-1) and-0.60%℃~(-1) over the range 20-100 ℃,compared to temperature coefficients of-0.117%℃~(-1)(α) and-0.74%℃~(-1)(β) in the regular magnets without Dy_(80)Ga_(20) powder.The irreversible loss of magnetic flux(Hirr) was investigated at different temperatures.After being exposed to 150 ℃ for 2 h,the Hirr of magnets with 4 wt.%Dy_(80)Ga_(20) decreased by ~95%compared to that of the undoped magnets.The enhanced temperature coefficients and Hirr indicate improved thermal stability in the doped Nd-Fe-B magnets.The intergranular addition of Dy_(80)Ga_(20) also improved the corrosion resistance of the magnets because of the enhanced intergranular phase.In a corrosive atmosphere for 96 h,the mass loss of the sintered magnets with 4 wt.%Dy_(80)Ga_(20) was 2.68 mg/cm~2,less than 10%of that suffered by the undoped magnets(28.1 mg/cm~2).     

Simultaneous enhancement in coercivity and remanence of Nd2Fe14B permanent magnet by grain boundary diffusion process using NdHx

We have successfully developed a Dy-free grain boundary diffusion process with neodymium hydride (NdH_x) alloy to the permanent magnet Nd₂Fe₁₄B powders using hydrogenation – disproportionation – desorption – recombination (HDDR) method. All the diffusion treatments were performed at 700–800 °C for various annealing time under the high vacuum with rotating diffusion method that effectively control the abnormal grain growth. The coercivities of Dy-treated Nd₂Fe₁₄B powders were varied from 9.5 kOe to 13.2 kOe but the remanence was decreased to 8.1 kG (10% reduction) depending on dysprosium hydride (DyH_x) content and diffusion treated time. However, the coercivity and remanence of Dy-free diffusion treated powder have been increased to 12.2 kOe (28.5% enhancement) and 11.1 kG (22% enhancement) at the optimal diffusion treatment (800 °C for 3 h), respectively. This unique simultaneous enhancement is to isolate the magnetic coupling between Nd₂Fe₁₄B grains by creating non-magnetic Nd grain boundaries and enhance the alignment of the Nd₂Fe₁4B hard magnetic phase, fabricated by optimal diffusion conditions.     

Changes of microstructure and magnetic properties of Nd-Fe-B sintered magnets by doping Al-Cu

The microstructural and magnetic properties of Al_100−xCu_x (15at%≤x≤45 at%) doped Nd-Fe-B magnets were studied. The distribution and alloying effects of Cu or Al on the intergranular microstructure were investigated by thermodynamic analysis, differential scanning calorimetery and microscopy techniques. It was observed that when the Cu content of Al_100xCu_x exceeds to 25 at%, the (Pr, Nd)Cu and CuAl₂ phases form in these magnets. The formation of (Pr, Nd)Cu phase depends on the negative formation enthalpy of (Pr, Nd)Cu and the exclusive distribution of Cu in the intergranular regions. The eutectic reaction between (Pr, Nd)Cu phase and (Pr, Nd) occurs at 480 °C, which forms the liquid phase that dissolves the (Pr, Nd)₂Fe₁₄B surface irregularities and thus increases the quantities of (Pr, Nd)-rich phase at the grain boundaries. These changes benefit the grain boundary microstructure, especially the distribution of (Pr, Nd)-rich phase, which effectively improves the intrinsic coercivity _iH_c due to the decreases of exchange coupling between the (Pr, Nd)₂Fe₁₄B grains.     

Influence of misch metal content on microstructure and magnetic properties of R–Fe–B magnets sintered by dual alloy method

MM_(14)Fe_(79.9)B_(6.1)/Nd_(13.5)Fe_(80.5)B_6 magnets were fabricated by dual alloy method(MM, misch metal). Some magnets have two Curie temperatures. Curie temperatures T_(c1)corresponds to the main phase which contains more La Ce, and T_(c1) decreases from 276.5?C to 256.6?C with the content of MM increasing from 30.3 at.% to 50.6 at.%. The variation of Br with the increase of MM indicates the existence of inter-grain exchange coupling in the magnets. When MM/R ≤ 30.3 at.%,the magnetic properties can reach the level of the intrinsic coercivity Hcj≥ 7.11 kOe and the maximum energy product(BH)max≥ 41 MGOe. Compared with Nd, La and Ce are easier to diffuse to the grain boundaries in the sintering process,and this will cause the decrease of H_(cj) Due to the diffusion between the grains, the atomic ratio of La, Ce, Pr, and Nd in each grain is different and the percentage of Nd in all grains is higher than that in misch metal.     

Texture analysis of ultra-high coercivity Sm_2Co_7 hot deformation magnets

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.