回火温度对晶界添加烧结钕铁硼磁体结构演变及磁性提升机理的影响EI北大核心CSCD

采用晶界添加的方法制备了添加Tb65Cu35的烧结Nd-Fe-B磁体,研究了回火温度对晶界添加磁体微结构演变规律及磁性能的影响,并对其性能提升机制进行了分析。结果表明：经910℃一级回火2 h,460℃二级回火2 h的磁体性能最佳,获得了Br=14.14 k Gs,Hcj=12.31 k Oe,(BH)max=47.89 MGOe的磁性能,回火后的磁体的矫顽力从10.21 k Oe提升到12.31 k Oe,增加了约20%,剩磁基本保持不变。矫顽力的提升主要归因于硬磁的(Nd,Tb)-Fe-B壳层以及连续晶界层的形成。通过一阶反转曲线(FORC)对不同回火条件下样品的磁化反转过程进行了分析,可以发现最差回火态晶界添加磁体中有两个峰,然而,最佳回火态的晶界添加磁体只有一个明显的峰,表现出明显的相互作用的单畴晶粒特性,表明最佳回火态磁体内核壳之间具有强的耦合相互作用。     

Hot deformation in nanocrystalline Ndben Feben B backward extruded rings

Radially oriented Nd-Fe-B rings are prepared by backward extrusion of fine grained melt-spun powder. Melt-spun powder with the nominal composition of Nd_30.5Fe_bal.Co_6.0Ga_0.6Al_0.2B_0.9 (wt%) is used as starting material. The effects of process variables, such as deformation temperature (T_d), strain rate (ε) and height reduction (Δh%), on the magnetic properties of the rings are investigated. A scanning electron microscope (SEM) equipped with an energy spectrum device is used to study the metallograph and microfracture of the extruded rings. The B_r and (BH)_max reach the optimum values at T_d=800℃, ε =0.01 mm/s, and Δh% =70%. It is found by SEM observations that the particle boundaries, which seemingly correspond to the interfaces of the starting melt-spun powders, emerge after the corrosion of metallography specimens. This is helpful for studying the effects of powder-powder interface on the local deformation and deformation homogeneity in the rings. For different spatial positions of the extruded rings, there are characteristic metallographies and microfractures. The upper end of the rings has the least deformation and worst texture, and therefore the worst magnetic properties. The magnetic properties in the radial direction increase slightly along the axis from the bottom to the middle, then steeply decrease at the upper end of the ring. The deformation and the formation-of-texturing processes are discussed. The deformation and the texturing formation of melt-spun Nd-Fe-B alloys probably involve grain boundary sliding and grain rotation, the solution-precipitation process and preferential growth of Nd₂Fe₁₄B nanograins along the easy growth a-axis.     

双合金结合速凝工艺制备烧结NdFeB研究

采用速凝工艺制备了主相合金铸片,由其微观形貌分析可见,富Nd相呈薄层状均匀分布在主相晶界处。XRD分析表明铸带形成了明显的取向织构。使用普通熔炼方法熔炼几种不同成分的辅相合金。将主相合金与辅相合金配比,运用双合金法工艺制备出烧结NdFeB磁体。研究表明Pr替代Nd有利于提高磁体的剩磁。     

CGNS API和FVM在非结构混合网格计算中的应用

用CGNS API（CFD General Notation System Application Programming Interface）作为非结构混合网格求解器的前处理和后处理，用FVM（Finite Volume Method）作为偏微分方程求解方法．在前处理过程中，用hash表法对内部网格面和边界网格面进行编号，并计算出相应的几何信息，以满足FVM求解器的需要．从FVM求解器计算出来的各种场信息可以写入原来的CGNS文件，该文件可以被许多专业商业后处理软件（如Tecplot，Fluent，CFX等）读取和进行可视化；对于求解器，用基于网格中心的FVM及SIMPLEC（Semi Implicit Methodfor Pressure Linked Equation Consistent）方法求解压力速度耦合．最后给出两个说明算例．     

高矫顽力HDDR各向同性Nd-Dy-Fe-Co-B黏结磁体的磁性能与微结构

研究了添加微量元素Co和Dy对HDDR工艺制备各向同性Nd-Dy-Fe-Co-B粘结磁体磁性能的影响. 结果表明, (Nd_0.65Dy_0.35)12.5(Fe_0.9Co_0.1)₈₁B_6.5磁体的内禀矫顽力H_cj高达1.53 MA·m^-1,剩磁的可逆温度系数为-0.059%/℃（25～155℃）. 使磁体具有高矫顽力、低温度系数的原因一方面是由于Dy和Co的加入提高了硬磁性相的各向异性场和T_C温度,另一方面是由于材料显微结构的改善.     

纳米Nd2Fe14B永磁材料的有效各向异性随晶粒尺寸的变化

以纳米Nd2Fe14B硬磁材料为例, 从Herzer的随机各向异性理论出发, 采用立方体晶粒结构模型, 建立了纳米硬磁性晶粒之间的部分交换耦合模型, 研究了材料的有效各向异性随晶粒尺寸的变化关系.结果表明: 晶粒之间的交换耦合相互作用随晶粒尺寸的减小而增强, 材料的有效各向异性Keff随晶粒尺寸的减小逐渐下降. Keff随晶粒尺寸的变化规律与矫顽力的变化规律基本相似, 纳米Nd2Fe14B硬磁材料矫顽力的下降主要由有效各向异性的减小引起.     

Nd-Fe-B速凝带的研究现状

在烧结钕铁硼中存在着大量的α-Fe相,这是高温凝固时析出相,它的出现占据了应形成为主相的Fe的位置,致使主相数量减少。主相减少会使剩磁降低,而且α-Fe本身作为软磁性相会降低磁体的矫顽力。速凝工艺能快速冷却,可以很好地抑制α-Fe产生。对速凝带的一些研究进行了总结,并介绍了研究结果,解释了速凝带中自由面微晶区出现的原因,最先提出速凝带最佳结构为柱状晶与贴辊面垂直的结构,这种结构柱状晶晶粒比一般结构柱状晶晶粒平均值小0.38μm。     

热流变速率对纳米晶Nd-Fe-B磁体性能的影响

通过对不同流变速率6)ε下磁体的微观结构和磁性能的分析,研究了流变速率对纳米晶Nd-Fe-B磁体性能的影响。结果表明,在流变速率从0.0025 s~(-1)增加至0.0075 s~(-1)过程中,磁体的矫顽力、剩磁和最大磁能积都是先增大后减小,并在6)ε=0.0050 s~(-1)时达到最大值。在流变速率为0.0050 s~(-1)时,细小晶粒沿着压力方向取向排布最为规则。XRD显示在0.0050 s~(-1)时,磁体取向度最好。磁体沿易磁化轴(∥c)和难磁化轴(⊥c轴)方向的磁化曲线表明,相对于其他的流变速率,流变速率为0.0050 s~(-1)时,沿着c轴方向的磁化最容易,垂直于c轴方向的磁化最难,与微观结构观察结果吻合。制备的性能最佳磁体的晶粒大小为长约700 nm,宽约150 nm,其磁性能为Br=14.51 k Gs,Hcj=9.09k Oe,(BH)max=52.74 MGOe。     

Effects of spacer layers on magnetic properties and exchange couplings of Nd-Fe-B/Nd-Ce-Fe-B multilayer films

The influences of the spacer-layer Ta on the structures and magnetic properties of Nd Fe B/Nd Ce Fe B multilayer films are investigated via DC sputtering under an Ar pressure of 1.2 Pa. An obvious(00l) texture of the hard phase is observed in each of the films, which indicates that the main phase of the film does not significantly change with Ta spacer-layer thickness. As a result, both the remanence and the saturation magnetization of the magnet first increase and then decrease,and the maximum values of 4πM_r and H_(cj) are 10.4 k Gs(1 Gs = 10_(-4)T) and 15.0 kOe(1 Oe = 79.5775 A·m_(-1)) for the film with a 2-nm-thick Ta spacer-layer, respectively, where the crystalline structures are columnar shape particles. The measured relationship between irreversible portion D(H) =-?M_(irr)/2 M_r and H indicates that the nucleation field of the film decreases with spacer layer thickness increasing, owing to slightly disordered grains near the interface between different magnetic layers.