Evolution of crystallographic alignment in Tb-Fe-B melt-spun ribbons

Ternary Tb-Fe-B ribbons were prepared via melt-spun technique under different wheel speeds of 5-25 m/s.Effect of wheel speed on the crystal structure and microstructure of the ribbons was investigated.All the ribbons quenched under different wheel speeds crystallized in single Tb2Fe14B phase with tetragon structure.Different crystallographic alignment evolutions were observed in the free side surface and wheel side surface of the ribbons.On the free-side surface,an in-plane c-axis crystal texture of Tb2Fe14B phase was found in the ribbons quenched at 5 m/s.However,with the increase in the wheel speed,the direction of the c-axis texture turns to perpendicular to the ribbon surface.On the wheel-side surface,a strong c-axis texture perpendicular to the ribbon surface was observed in the ribbons quenched at 5 m/s,and then weakened gradually with the increase in the wheel speed.Further investigation showed that the competition of the two types of temperature gradients during the quench process was responsible for the crystallographic alignment evolution in the ribbons.     

High cerium content(Nd-Pr-Ce)2Fe14B melt-spun ribbons with high coercivity

The effects of wheel speeds on the magnetic properties and microstructures of [(Nd,Pr)_1-xCe_x]-Fe-B meltspun 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 ...     

Effect of Cobalt on HDDR Anisotropic NdFeB

The effect of cobalt on the magnetic properties and anisotropy of HDDR anisotropic NdFeB was studied.It is found that Co is helpful for preparing anisotropic NdFeB with high coercivity. The research on the initial microstructure for NdFeB alloy indicates that Co tends to enter the crystal lattice of Nd-rich phase and some of Co atoms also enter the crystal lattice of Nd2Fe14B. The dissolution of Co changes the stability of Nd-rich phase and Nd2Fe14 B in H2 atmosphere and affects the kinetics of HDDR phase transformation. As a result, the NdFeB powder exhibits a high coercive force and a strong anisotropy.     

Preferred Orientation in Nanocomposite Permanent Magnet Materials

Melt-spun （Nd11.4Fe82.9B5.7）0.99M1 ribbons （M = Zr, Nb, Ga, Zr＋ Ga, Nb ＋ Ga）were prepared by melt-spinning technique. Ga addition is found to be effective for the orientation of c-axis of Nd2Fe14B grains perpendicular to the ribbon plane. Better magnetic properties can be achieved by adding both the two kinds of elements Zr ＋ Ga, Nb ＋ Ga, and it is found that the preferred orientation is further improved. The alignment degree changes with ribbon thickness and is highest when ribbon thickness is 120 μm. Heat treatment can improve the texture degree, but lead to coarser grains. Cryogenic treatment is first applied for the treatment of nanocomposite Nd2Fe14B/α-Fe melt-spun ribbons. The effects on magnetic properties and texture degree of nanocomposite magnets after cryogenic treatment were studied. The result shows that cryogenic treatment is beneficial to the enhancement of texture degree of melt-spun ribbon and the grain size has no obvious change.     

Influences of Niobium and Zirconium Additions on Crystallization Behaviors and Magnetic Properties of Melt-Spun （Nd, Pr）2Fe14B／α-Fe Alloys

Effects of Nb and Zr substitutions on the crystal]ization behaviors and magnetic properties of melt-spun (Nd,Pr)2Fe14B/α-Fe alloys were studied.The results show that for (Nd0.4Pr0.6)8.5Fe85.5B6 ribbons, the metastable (Nd,Pr)3Fe62B14 precipitates after the initial crystallization of α-Fe and decomposes into the final mixture of (Nd,Pr)2Fe14B and α-Fe. For(Nd0.4 Pr0.6)8.5 Fe84.5 Zr0.5 Nb0.5B6 ribbons, however,(Nd, Pr)2Fe14B and α-Fe phases precipitate simultaneously. This indicates that both Nb and Zr dopingcan avoid the formation of metastable phase and!     

Coercivity enhancement of Nd2Fe14B/α-Fe nanocomposite magnets through neodymium diffusion under annealing

The coercivity enhancement of ball-milled Nd2Fe14B/α-Fe nanocomposite magnets was investigated. It was found that the coercivity could be enhanced through mixing a small amount of Nd powder with as-milled Fe-rich Nd-Fe-B powders. The annealed samples were investigated by means of X-ray diffraction, scanning electron microscopy and magnetic measurement systems. Under annealing, some of Nd powders promoted the formation of hard magnetic phase Nd2Fe14B. On the other hand, a few of Nd would diffuse into the interface of Nd2Fe14B/α-Fe nanocomposite to compensate for the loss of the interfacial magnetic anisotropy. These two features are all beneficial to the coercivity.     

The microstructure and magnetization reversal behavior of melt-spun (Nd1−xCex)-Fe-B ribbons

In this study,the alloy ingots with nominal compositions of(Nd_(1-x)Ce_x)_(31)Fe_(bal)Co_(0.2)Ga_(0.1)B(x=0, 0.1 wt%,0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%) were prepared and then melt-spun to form nanocrystalline ribbons at the wheel speed of 20 m/s. XRD results show that all melt-spun ribbons exhibit the tetragonal structure(Nd,Ce)_2 Fe_(14)B phase with the space group P42/mmm. The Curie temperature and lattice constant decrease with the increase of Ce content. The Curie temperature decreases gradually from 306 to 247 ℃with the increase of Ce content. Those results indicate that Ce element has been incorporated into Nd_2 Fe_(14)B main crystalline phase and formed(Ce,Nd)-Fe-B hard magnetic phase. It is also found that the remanence ratio(M_r/M_s) decreases from 0.693 to 0.663 and the coercivity(H_c) decreases from 18.7 to14.2 kOe with the increase of Ce content. However, a relatively high coercivity of 18.3 kOe for(Nd_(1-x)Ce_x)_(31)Fe_(bal)Co_(0.2)Ga_(0.1)B(x = 0.2) melt-spun ribbon is achieved. The coercivity is sensitive to microstructure. The AFM patterns show the sample(x = 0.2) has the most uniform and finest microstructure. The magnetization reversal behavior(δM plots) is discussed in detail. The positive δM value is observed in every sample, which confirms the existence of exchange coupling interaction. Evidently, theδM maximum value reaches 0.9 in the sample(x = 0.2). It is indicated that the intergranular exchange coupling effect is the strongest, which is consistent with coercivity enhancing.     

Magnetic Properties of Melt-Spun Nanocomposite PrloFe74-x Co10＋x C4B4（x=0,2,4,6,8） Ribbons

Phase evolution and magnetic properties of melt-spun Pr10Fe74-xCo10 xC4B4(x=0,2,4,6,8 ) alloy ribbons were investigated. Increasing the Co content is found to promote the generation of the 2: 14:1 phase, which results in a significant increase of coercivity and remanence.     

Effect of magnetic layer thickness on magnetic properties of Ce-Fe-B thin films

The Ce_2 Fe_(14)B thin films with a notable out-of-plane c-axis texture were prepared by DC magnetron sputtering on a Ta buffer layer. The morphological and magnetic properties were investigated. The thickness of the magnetic layer had a dramatic effect on the formation of Ce_2 Fe_(14)B phase,and excellent magnetic properties(H_(ci)≈4.25 kOe, M_r/M_s≈0.81) were observed for the Ce-Fe-B film with the thickness d_m = 200 nm. The results of the hysteresis loops for Ce-Fe-B film(d_m = 200 nm) at various measured temperatures show that a decoupling between the hard and the soft phases is observed at low temperatures, which is due to the regions with quite low anisotropy provided by the a-Fe. Moreover. it is clear that significantly various magnetization behaviors between the films with d_m = 200 and 300 nm were observed with a similar trend due to the existence of the a-Fe soft phase.     

Differences of element distribution between free and wheel side surface of NdFeB/α-Fe ribbons

The ribbons of NdFeB/α-Fe composite alloy were prepared by melt spinning and post crystallizing technique.The element distri-butions and phase component of both surfaces of as-spun ribbons were measured by energy dispersive spectrometry (EDS) and X-ray diffrac-tion (XRD).Because of the centrifugation,a segregation of B,Fe,and Nd concentrations was observed at the cross section.After crystallizing annealing,the element concentration segregation still existed in the as-crystallized ribbons.Due to the segregation of B,Fe,and Nd,the B-rich phase was observed near the wheel side surface.The B-rich phase may deteriorate the magnetic property of NdFeB/α-Fe composite alloy.     

Effects of magnetic annealing on crystallization and magnetic properties of Nd2Fe14B/α-Fe nanocomposite magnets

Crystallization and magnetic properties of Nd2Fe14B/α-Fe nanocomposite magnets have been investigated by annealing the as-spun ribbons with magnetic field.The crystallization process was accelerated by field annealing.The hysteresis loop became to be fat by magnetic annealing at 645 oC for 4 min,which was 690 oC for ribbons annealing without magnetic field.The relative content of α-Fe phase was increased from the results of XRD.The strength of the magnetic field had no obvious influence on the remanence and coercivity,but modified the squareness of hysteresis loop.     

Microstructure and electrochemical properties of melt-spun Nd_(0.8)Mg_(0.2)(Ni_(0.8)Co_(0.2))_(3.8) hydrogen storage alloy

The effects of rapid solidification on the microstructure and electrochemical properties of Nd0.8Mg0.2(Ni0.8Co0.2)3.8 alloy were systematically investigated.The microstructure of alloys was characterized by scanning electron microscopy(SEM),X-ray diffractometer(XRD) and transmission electron microscopy(TEM).It was found that the melt-spun Nd0.8Mg0.2(Ni0.8Co0.2)3.8 ribbons became thinner and the average grain size of the ribbons became smaller with increasing wheel speed.A fraction of amorphous phase was observed for the ribbons melt-spun at high wheel speed(≥20 m/s).Microstructural characterization revealed that two phases:(Nd,Mg)2(Ni,Co)7 main phase(Ce2Ni7 type structure) and NdNi5 second phase(CaCu5 type structure),existed in the samples in cast state and melt-spun.The cycle stability of the melt-spun alloys was significantly enhanced as compared with cast alloy,and the sample prepared at wheel speed of 20 m/s exhibited good comprehensive electrochemical properties.     

Easy-Magnetization-Axis Arrangements of Sm2Co17 and RE2Fe14B

In order to prepare the bulk samples with high residual magnetization of magnetic compounds, such as (Sm,La)2(Co,Cu,Fe,Zr)17, (Sm,La)1(Co,Cu,Fe)5, Nd2Fe14B, and Pr2Fe14B, directly prepared by solidification, or hot-deformation, it is the first thing to explore the possibilities of the easy magnetization axis of the whole bulk samples to be arranged in one designed direction. α is defined as the angle between the axis and the direction. In Sm-La-Co-Fe-Cu-Zr system, whether α is equal to 0° or 90° depends upon not only alloy compositions but also the ratio of the temperature gradient at the solid/liquid interface and the crystal growth rate. To some alloys, α can be changed from 90° to 0° if the ratio is increased to be higher than a critical value, so the c-axis texture orientation can be obtained. In Nd-Fe-B system, the easy magnetization axis of Nd2Fe14B is always perpendicular to the preferential growth direction [100], and the easy magnetization axes of Nd2Fe14B grains are randomly distributed in the plane normal to the growth direction even if the growth rate is decreased from 250 to 12 μm·s-1. But if the magnetization axis of the anisotropic magnet substrate is perpendicular to the heat flux direction of the laser melting solidification layer, c-axis texture of the columnar Nd2Fe14B grains in the layer can be obtained, which is the same as that of the substrate, if the laser scanning rate is not less than 25 μm·s-1. Also the c-axis texture [006] can be achieved through hot-deformation of PrxFe93.5-xB5Cu1.5 (x=15～19) under the conditions of hot-pressing temperature 973～1273 K, strain rate 10-3 S-1, and strain 50%～80%.     

Effect of high pressure on microstructure of crystallizing amorphous Nd9Fe85B6 alloy

The effect of high pressure on the microstructure of annealed amorphous Nd9Fe85B6 alloy was studied. It was found that application of high pressure made the microstructure of the crystallized alloy much more homogeneous. The average grain size of the Nd2Fe14B phase decreased with the increase of pressure, whereas, the size of the α-Fe first increased when a pressure of 1 GPa was applied and then decreased with further increase of pressure. Pressure-induced （410） texture of the Nd2Fe14B phase was also observed. The present study suggested an effective route for controlling the microstructure in a nanoscale solid.     

Zirconium content induced mitigation of mechanical anisotropy in 2:17 type SmCo magnets

The mitigation of mechanical anisotropy is observed in 2:17 type SmCo magnets by adjusting the Zr content This behavior is supposed to be closely related to the density of lamellar phase,the density of which is enhanced obviously with increasing Zr content.The other reasons which could cause the reduction of the mechanical anisotropy is discussed from the Zr-rich impurity phase to the atom substitutions and crystal lattice distortion.The observation of crack in nano scale that dearly forms angles of 60° and 90° with respect to the lamellar phase,indicates that the probable cleavage planes are crystal faces(1011) and(1010).The results of investigation can deepen the understanding of mechanical anisotropy and cleavage fracture in the SmCo magnets.     

Solidification Behavior of Laser Melting Layer of Nd15Fe77B8 Sintered Magnets and Its Microstructures Evolution

To research the solidification behavior and microstructures of a laser remelting/solidification layer on anisotropic Nd15Fe77B8 sintered magnets with their magnetization direction parallel to X, Y, Z-axis respectively, their surfaces (parallel to XOY plane) were scanned by 5 kW Roffin-Sinar 850 type of CO2 laser along Y axis. The rapid solidification of the molten alloy in the layer results in three distinct zones. The transition zone close to the unmolten portion of a magnet (substrate), consists of the columnar Nd2Fe14B phase (matrix), the 10.0%～15.1% dendrite primary iron phase dispersing in the matrix, and the Nd-rich phase along Nd2Fe14B grain boundaries. The columnar crystal zone in the middle of the layer consists of the long columnar Nd2Fe14B grains and their grain boundary Nd-rich phase. And the dendrite crystal zone near the free surface of the layer consists of dendrite Nd2Fe14B grains and their grain boundary Nd-rich phase. When the laser scanning velocity is lower, the growing direction of the microstructures in the layer tends to the laser scanning direction step by step. When the velocity is not lower than 25 mm · s-1, the laser remelting/solidification layer thins and the columnar crystal zone comprises almost the whole layer. Under this condition, on the substrate with its magnetization direction along X or Y-axis respectively, the columnar Nd2Fe14B grains in the layer grow in the direction of Z-axis (that is their long-axis along Z-axis), their alignment of the easy magnetization axis [001] is parallel to the magnetization direction of the substrate correspondingly; but on the substrate with its magnetization direction along Z-axis, the columnar Nd2Fe14B grains in the transition zone grow at an angle of 30°～50° between Z-axis and their long-axis. And the columnar Nd2Fe14B grains in the columnar crystal zone gradually tend to the Z-axis,and their easy magnetization axis [001] arrange in the range of 0°～360° of the plane perpendicular to their long-axis.     

Effect of yttrium substitution on magnetic properties and microstructure of Nd-Y-Fe-B nanocomposite magnets

The phase evolution,microstructure and magnetic properties of Nd9-xYxFe72Ti2Zr2B15(x=0,0.5,1,2) nanocomposite ribbons were investigated.It was found that substitution of Y enhanced glass forming ability of the over-quenched ribbons and stabilized the amorphous phase during post annealing treatment.Appropriate content of Y substitution effectively refined the microstructure and enhanced the remanence of the annealed samples.The residual amorphous intergranular phase in the annealed sample improved the square...     

Microstructure and corrosion resistance of sintered NdFeB magnet modified by intergranular additions of MgO and ZnO

Microstructure and corrosion resistance of sintered Nd15Dy1.2Fe77Al0.8B6 and Nd22Fe71B7 magnets modified by intergranular addition of MgO and ZnO were investigated. Both the remanence and sintering density of the magnets increased slightly with intergranular additions of MgO and ZnO. There was a remarkable increase in coercivity of Nd22Fe71B7 after addition. Besides, the effects on magnetic properties and an improved corrosion resistance were observed. Compared with the native magnets without addition, corrosion potential of the magnets with MgO and ZnO additives was more positive and the current density in the anodic branch of the polarization curve was reduced. Corrosion resistance resulting from autoclave testing （2×10^5 Pa of steam pressure, 120 ℃） showed that the corrosion rate of NdFeB magnets reduced with the increase of additive amount. Microstructure observation revealed that MgO and ZnO additives were incorporated into the intergranular phases in the magnets. With the introduction of MgO and ZnO, more intergranular phase with high oxygen content was formed while keeping the volume fraction of all the intergranular phases almost unchanged, which may contribute to improved corrosion resistance. Furthermore, addition of MgO and ZnO refined the grain size of Nd22Fe71B7.     

Effect of super heat treatment on crystallization behavior and magnetic properties of Nd4.5Fe77B18.5 nanocomposites

Melt-spun Nd4.5Fe77B18.5 ribbons were prepared under various superheat temperatures.The microstructure characteristics,crystallization behavior,and subsequent magnetic properties of Fe3B/Nd2Fe14B nanocomposite magnets were investigated using X-ray diffraction,differential thermal analysis,and vibrating sample magnetometry.It was shown that melt spinning at different quenching temperatures caused the as-quenched ribbons to have distinctive crystallization behavior.Depending on superheat temperature,phase tra...     

Effect of titanium addition on the magnetic property of Nd2Fe14B/α-Fe nanocomposite alloys

Rapidly solidified nanocrystalline α-Fe/Nd2Fe14B alloys with enhanced coercivity were obtained by melt spinning.The effects of Ti addition on the microstructore and magnetic properties of the nanocomposite α-Fe/Nd2Fe14B alloys were investigated by X-ray diffraction(XRD)and superconducting quantum interference device(SQUID)magnetometer.The analysis of XRD showed that Vα-Fe estimated to be about 35.3% in the Ti-free α-Fe/Nd2Fe14B nanocomposites decreased down to 26.5% as the addition of was 5 at.% Ti.Accordingly,adding Ti resulted in relevant improvements of magnetic properties,especially of the coercivity Hc from 595 kA/m up to 1006 kA/m.The dependence of Mirrev(H)/2Mr on the reverse field H indicated that nucleation was the dominating mechanism for the magnetization reversal in these nanocomposites.The analysis of the temperature dependence of the demagnetization curve in the α-Fe/Nd2Fe14B nanocomposite magnets indicated that a reduction of αex could play a leading role in an increase in the coercivity of Ti-doped sample.