The correlation between hydrogen absorption capacity (HAC) and the microstructure of Sm26.2CobalFexCu4.0Zr2.3 (x = 23 wt%, 25 wt%, 27 wt%, 30 wt%) ingots and cast strips was systematically investigated. As the temperature rises from 373 to 423 K, the activation time, hydrogen absorption time and HAC of the Sm26.2CobalFe23Cu4.0Zr2.3 ingot decrease by 14.4%, 14.1%, and 19.3%, respectively. Dispersed 1:5 phase provides more channels for hydrogen diffusion, which is the main reason that HAC increases with the x increasing. The HAC of the same compound strips increases as the particles size of the pre-crushed decreases. However, no further embrittlement behavior appears in pre-crushed strips, which reaches an equal HAC as ingots. Micro-computerized tomography reveals that ingots contain small spherical-like holes and large flake micro-cracks, whereas strips mainly contain elliptical pores. The effects of grain size and inner defects size on structure stability were invested by Abaqus. Simulation results reveal that the superior embrittlement behavior of the ingots is predominantly influenced by the presence of large flake-like micro-cracks.

The hydrogenation kinetics of Sm26.2CobalFexCu4.0Zr2.3 (x = 23, 27 in wt%) strips (Fe23 and Fe27 strips) has been investigated. The phase composition, morphology, surface roughness and the inner pores of the strips also have been studied by XRD, SEM, optical profilometer and non-destructive micro-computerized tomography. Compared to Fe23 and Fe27 strips, heat-treated strips (H-Fe23 and H-Fe27) and corrosion heat-treated strips (HC-Fe23 and HC-Fe27) exhibit a relatively higher hydrogen absorption capability. Fragmentation behavior occurs in HC-Fe23, H-Fe27 and HC-Fe27 strips during hydrogenation. After heat treatment, the grain size and inner pore size increase, leading to the disappearance of fine crystal strengthening and the concentration internal stress. For corrosion-treated strips, increased surface roughness and deeper grooves result in the formation of surface stress concentration, ultimately leading to an increased susceptibility to hydrogen embrittlement. Accordingly, the increase of grain size, inner pore size and rougher surface is beneficial for hydrogenation and hydrogen embrittlement.

The diffusion behaviors of hot-deformed magnets were investigated in two different directions with additional pressure. For magnets diffusion along the direction parallel to the C-axis (IIC magnets) and magnets diffused perpendicular to the C-axis (1C magnets), the coercivity increased by 3.66 kOe and 4.94 kOe, while the remanence decreased by 1.39 kGs and 1.04 kGs, respectively. The coercivity and remanence are both higher in 1C magnets as compared to IIC magnets. SEM indicates that the orientation in 1C magnets is better than in IIC magnets, which contributes to the more excellent remanence. The SEM also suggests the distribution of the rareearth-rich phase was more uniform in 1C magnets. EPMA shows that the diffusion depth of 1C magnets reaches around 1500 mu m, while IIC magnets is less than 1250 mu m. Both the homogeneous distribution of the rare-earthrich phase and deeper diffusion depth are responsible for the improved coercivity of 1C magnets. EDS shows that the Nd 70 Cu 30 preferentially entered the interior of the magnets through the interface formed by the fine grains of melt-spun ribbon edges for IIC magnet during grain boundary diffusion process. But the 1C magnet did not show this preference during diffusion. The grain morphology and diffusion resistance of magnets in different directions is the fundamental cause for the difference of Cu distribution in IIC magnet and 1C magnet. The initial magnetization curves suggests that the coercivity mechanism of the initial magnets combines nucleation and domain wall pinning, while the domain wall pinning is enhanced for the diffused magnets. The optimum performances with B r = 13.21 kGs, H cj = 18.23 kOe, and (BH) max = 43.01 MGOe were achieved in 1C magnets.

The effects of wheel speeds on the magnetic properties and microstructures of[(Nd,Pr)1-xCex]-Fe-B melt-spun ribbons were investigated.Compared to melt-spun ribbons with low cerium(Ce)content(x=0.2),amorphous formation can be suppressed at high wheel speed in the ribbons with a relatively high Ce content(x=0.8),and with the increase of the wheel speed,the magnetic properties of the ribbons with high Ce content raise continuously.At high wheel speed,the coercivity mechanism of melt-spun ribbons is mainly pinning field,and the high wheel speed introduces a large number of defects into the matrix as pinning sites.Furthermore,ribbons with high Ce content form a fine and uniform grain structure,so the grain boundary area enlarges,which further hinders the movement of domain walls.The combined effects of the above factors enable ribbons with high Ce content to have excellent magnetic properties(Hcj=0.977 T,Mr=64 m2 A/kg)at the wheel speed of 35 m/s.

The effects of melt-spinning speed ( v=15, 20, 25, 30, 35 m/s) and heat-treatment process on the magnetic properties and microstructure of melt-spun Nd26Pr3FebalCo4Ga0.42B0.92 ribbons were investigated. The ribbons show an obvious orientation when the speed is less than 25 m/s in the free side, and c-axis is perpendicular to the strip surface; the orientation decreases with the increase of melt-spinning speed. The grain can be refined by increasing the melt-spinning speed. When v<25 m/s, the initial magnetization curve shows a one-step magnetization process, and demagnetization curve have good squareness. When v >= 25 m/s, the amorphous phase content increases obviously, the initial magnetization curve changes to two-step magnetization process, and the demagnetization curve collapses obviously. The best magnetic properties B-r=0.80 T, mu H-0(cj)=1.56 T, ( BH)(max)=108.22 kJ/m(3) are obtained under v=25 m/s. After optimum crystallization annealing treatment, the amorphous phase content reduces significantly, all of the magnetic properties of ribbons improve obviously at v <= 25 m/s. Squareness and coercivity increase remarkable at v> 25 m/ s; The ribbon prepared at v=35 m/s possesses the highest coercivity (mu H-0(cj)=2.10 T). The best magnetic properties B-r=0.91 T, mu H-0(cj)=1.82 T, (BH)(max)=141.65 kJ/m(3) are obtained under v= 30 m/s. The microstructure changes along with the thickness direction. The wheel side is composed of amorphous and fine grains, the free side is composed of larger grains. After the heat-treatment, the amorphous phase content is reduced significantly.

通过对不同流变速率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-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-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 kGs,Hcj=9.09kOe,(BH)max=52.74 MGOe.

Effects of low-melting Pr–Cu alloy addition on the microstructure and magnetic properties of the hot-deformation Nd–Fe–B magnets were investigated. A small amount of Pr–Cu addition enhances the coercivity of the hot-deformation Nd–Fe–B magnets obviously. The coercivity of the hot-deformation Nd–Fe–B magnets with 4.0 wt% Pr85Cu15 addition increases to 1271 kA·m−1, 75.69% higher than that of Pr–Cu-free magnet (723 kA·m−1), and then decreases with 5 wt% Pr85Cu15 addition. It is observed that there a uniform RE-rich phase is formed wrapping the Nd2Fe14B main phase in the sample with 4.0% Pr85Cu15 addition by scanning electron microscopy (SEM), which promotes the coercivity. The angular dependence of coercivity for the hot-deformation Nd–Fe–B magnets indicates that the coercivity mechanism is nucleation combined with domain wall pinning. The domain wall pinning is weakened, while the nucleation is enhanced after Pr–Cu addition. The remanence, intrinsic coercivity, and maximum magnetic energy product of the original Nd–Fe–B magnet are 1.45 T, 723 kA·m−1, and 419.8 kJ·m−3, respectively, and those of the sample with 4.0% Pr85Cu15 alloy addition are 1.30 T, 1271 kA·m−1, and 330.0 kJ·m−3, respectively.

The magnetic properties, microstructure and orientation degrees of hot pressing magnet and hot deformation Nd-Fe-B magnets with different deformation ratios have been investigated in this paper. The remanence (Br) and maximum magnetic energy product ((BH)max) were enhanced gradually with the deformation ratio increasing from 0% to 70%, whereas the coercivity (HCj) decreased. The scanning electron microscopy (SEM) images of fractured surfaces parallel to the pressure direction during hot deformation show that the grains tend to extend perpendicularly to the c-axes of Nd2Fe14B grains under the pressure, and the aspect ratios of the grains increase with the increase of deformation ratio. Besides, the compression stress induces the long axis of grains to rotate and the angle (θ) between c-axis and pressure direction decreases. The X-ray diffraction (XRD) patterns reveal that orientation degree improves with the increase of deformation ratio, agreeing well with the SEM results. The hot deformation magnet with a deformation ratio of 70% has the best Br and (BH)max, and the magnetic properties are as followed: Br=1.40 T, HCj=10.73 kOe, (BH)max=42.30 MGOe.

Nd-Fe-B magnets have high magnetization and maximum energy product while PrCo 5 magnets have high Curie temperature and thermal stability .The anisotropic Nd-Fe-B/PrCo5 hybrid magnets were prepared by hot-pressing and deformation method using Nd-Fe-B melt-spun powders and PrCo5 powders.The results of X-ray diffraction (XRD), scanning electron microscope (SEM) and ther-mal magnetic analysis (M-T curve) indicated that the Pr-Co alloy in the hybrid magnets still possessed the PrCo 5 structure.The hyster-esis loops along different directions of the hybrid magnets and the patterns of XRD showed the hybrid magnets were changing from isot -ropy to anisotropy .SEM images showed that the PrCo 5 got together in the form of large particles and the orientation of the Nd 2 Fe14 B a-round PrCo5 was deteriorated.It was found that a complex transition layer appeared in the interface of the two phases , which resulted from the diffusion between Nd 2 Fe14 B and PrCo5 .The transition layer deteriorated the magnetic properties .The peak of the normalized reversible demagnetization curve of the hybrid magnets around the coercivity was irrelevant with anisotropy , because there might exist exchange-coupling effect between the transition layer and the matrix .The properties of the hot-deformed hybrid magnet were: Br =1.323 T, Hcj =682.2 kA·m-1, (BH)m =239.6 kJ·m-3.

采用钕铁硼快淬磁粉与快淬PrCo5混合热压的方法,制备了各向同性热压混合磁体.XRD,SEM,热重分析(TG)均表明混合磁体中PrCo5仍以1∶5相的状态存在.SEM观察表明所添加PrCo5以较大的颗粒聚集形式存在.当添加量较小时,混合磁体表现出单一的磁化行为,矫顽力变化较小,剩磁均随着PrCo5添加量的增加而逐渐降低,而当添加量达到16％(质量分数)时,退磁曲线上则表现出两相共存的磁化现象.δM曲线表明两相间存在着一定的交换耦合作用,添加PrCo5使得晶粒间交换耦合作用增强.当添加8％ PrCo5时,剩磁比(Mr/M3T)值从未添加的0.701增加到0.721;同时磁体的矫顽力温度系数有所改善,在300～ 360 K区间内,矫顽力温度系数β值由未添加的-0.418％·K-1变化到添加量8％时的-0.406％·K-1.