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The ultra-thin (Fe83Ga17)99.9(NbC)0.1 sheets with the thickness of 0.06–0.15 mm were prepared from the secondary recrystallized sheets via rolling. The recrystallization texture evolution, magnetostriction and mechanical properties in the rolled sheets during the annealing at 1200 °C for 1.5–3 h were investigated. Results indicated that the magnetostriction of the ultra-thin sheet was closely related to the texture evolution depended on heat-treatment process. The major textures in the as-rolled sheet were {113}<361> and {111}<112> deformed texture, and the saturation magnetostriction was only ~ 63 ppm. However, an ideal {100}<001> texture was obtained in the recrystallized sheets annealed at 1200 °C for 2 h, producing a corresponding magnetostriction of 147 ppm. Based on texture analysis, the appearance of cubic texture is mainly the consequence of the existence of cubic nuclei and transitional orientation {113}<361> in deformed grains as well as the lowest surface energy at the (100) plane. Compared with Goss secondary recrystallized (Fe83Ga17)99.9(NbC)0.1 sheet with a thickness of 0.3 mm, the tensile ductility of cubic recrystallized ultra-thin (Fe83Ga17)99.9(NbC)0.1 sheet was obviously improved from 2.4 to 4.4%, which was mainly attributed to the primary recrystallized microstructure with small grain size and transgranular fracture mode. The ultra-thin cubic textured (Fe83Ga17)99.9(NbC)0.1 sheets could significantly reduce eddy current losses at high frequency, and meet the requirements of low eddy current loss and high toughness for specific applications, such as ultrasonic applications and torque sensors. [ABSTRACT FROM AUTHOR]

Effects of Zr addition and annealing treatment on the formation, microstructure and magnetic properties of Nd12.3Fe81.7− x Zr x B6.0 ( x=0−3.0) ribbons melt-spun and annealed have been systematically investigated by means of vibrating sample magnetometer (VSM), differential scanning calorimeter (DSC), X-ray diffraction (XRD), and high resolution scanning electron microscopy (HRSEM). Phase analysis reveals that Nd2Fe14B is single-phase material. It has been found that the intrinsic coercivity H ci of the optimally processed Nd12.3Fe81.7− x Zr x B6.0 ribbons increases monotonically from 751.7 kA/m for x=0 to 1005.3 kA/m for x=3.0. The remanence polarization J r and maximum energy product ( BH)max increase first with Zr addition, then slightly decrease with further increasing Zr content. Optimum magnetic properties with J r=1.041 T, H ci=887.5 kA/m and ( BH)max=175.2 kJ/m3 have been achieved for the ribbons with x=1.5. The significant improvement of magnetic properties originates from the finer grains of the ribbons by introducing Zr. [ABSTRACT FROM AUTHOR]

Fe83Ga17 alloy ribbons with four thicknesses were prepared by the melt-spun method. The measured results show that magnetostriction is related to the thickness of the ribbons, and its maximum value, −2100 ppm, has been obtained in the ribbon with a thickness of 75 μm. The results of the X-ray diffraction (XRD) and the differential scanning caloric (DSC) show that a phase with DO3 structure emerges in those ribbons with the thicknesses of 45, 55 and 75 μm, and a phase transition of A2 + DO3 → A2 occurred at 669°C for the ribbon with the thickness of 75 μm. The increase in the cooling rate can restrain the precipitation of the Ga-rich phase in the ribbon. It is considered that the giant magnetostriction of ribbons originates from the A2 + special DO3 structure and shape magnetic anisotropy. [ABSTRACT FROM AUTHOR]

High magnetostrictive strain has been obtained in Tb0.3Dy0.7Fe1.98 polycystalline samples with <1 1 3> crystal orientation. The λ40 and λ80 values are 1250 and 1550 ppm, respectively under a pressure of 6 MPa, which is better than that of samples with <1 1 2> crystal orientation. The observed morphologies indicate that the grains with <1 1 3> axial orientation grow in the form of sheet-like cellular crystals. A rare-earth rich phase (R = Tb, Dy), is distributed along the boundaries of the cellular crystals. The excellent magnetostrictive properties are related to the microstructure of the material. [Copyright &y& Elsevier]

• The GBDP magnets were prepared by TbF 3 through screen printing technology. • The application of pressure can reduce diffusion time to develop core–shell structure. • The diffusion behavior and the role of F element in GBDP magnets were explored. The screen printing technology (SPT) was utilized to prepare TbF 3 coatings on Nd-Fe-B magnets. The effect of pressure-assisted grain boundary diffusion on magnetic properties and microstructure of Nd-Fe-B magnet has been intensively investigated. The results indicated that the intrinsic coercivity increment (ΔH ci) enhanced with increasing diffusion temperature and time. Meanwhile, the pressure could promote grain boundary diffusion process and shorten diffusion time obviously. Microstructural and compositional analyses indicated that the appropriate temperature and time were essential to develop the core–shell structure within a certain depth, which played a key role in the coercivity enhancement of magnet. Meanwhile, the thickness and continuity of Tb-rich shells decrease with diffusion depth. Furthermore, the pressure can strengthen the adhesion of TbF 3 coatings to base magnet, promoting the diffusion of Tb element into deeper regions and the formation of Tb-rich shells. The diffusion behavior and role of F element in magnet were also explored. The results confirmed that the diffusion depth of F was close to that of Tb element. However, the F element did not diffuse into 2:14:1 phase but formed NdOF phase distributing at grain boundaries. [ABSTRACT FROM AUTHOR]

Highlights • Coercivities of PCA, PTCA-5, PTCA-20 magnets are 19.6 kOe, 24.1 kOe and 24.3 kOe. • Coercivity enhancement of PCA magnet is owing to magnetic isolation by Nd-rich GBP. • Coercivity enhancement of PTCA-20 magnet results from magnetic hardening by TRS. • Magnetic isolation and hardening result in coercivity enhancement of PTCA-5 magnet. Abstract Grain boundary diffusion process (GBDP) with low melting-point alloy ribbons, namely Pr 70 Cu 15 Al 15 (PCA), Pr 65 Tb 5 Cu 15 Al 15 (PTCA-5) and Pr 50 Tb 20 Cu 15 Al 15 (PTCA-20, at%), was applied to Nd-Fe-B sintered magnet (52 M) as thick as 6 mm. The coercivities of diffused magnets by PCA, PTCA-5 and PTCA-20 increase significantly to 19.6 kOe, 24.1 kOe and 24.3 kOe, respectively, from original 14.7 kOe. Microstructural investigations indicate that the coercivity enhancement of PCA magnet is mainly attributed to magnetic isolation by continuous Nd-rich grain boundary phases (GBP). However, the coercivity enhancement of PTCA-20 magnet is mainly owing to magnetic hardening by Tb-rich shells (TRS), and that of PTCA-5 magnet results from a combined strengthening of magnetic isolation by GBP and magnetic hardening by TRS. Meanwhile, the coercivity of PTCA-5 magnet is as high as that of PTCA-20 magnet, but the former consumes Tb only 0.60 wt%, lower than 1.23 wt% for the latter. [ABSTRACT FROM AUTHOR]

In this work, 〈1 0 0〉 textured Co 70 Fe 30 alloy was successfully prepared by directional solidification technique. The effect of heat treatment on magnetostriction and microstructure of Co 70 Fe 30 alloy has been investigated. The Co 70 Fe 30 alloy was annealed in argon atmosphere at 700 °C–900 °C for 9 days and then cooled to room temperature by slow cooling or quenching. The magnetostriction as large as 180 ppm has been achieved for the quenched samples when the annealing temperature is ranging from 820 °C to 860 °C. Structural analyses indicate that the large magnetostriction originates from precipitation of a nanoscale face-centered tetragonal (fct) phase embedded in a body-centered cubic (bcc) phase matrix. [ABSTRACT FROM AUTHOR]

In this work, 0.5 mm diameter magnetostrictive (Co 70 Fe 30 ) 99.8 (NbC) 0.2 wires were prepared using forging and drawing processes. A Wiedemann twist up to 1348″/cm has been achieved in the annealed wires and to our knowledge is the largest value of Wiedemann effect in magnetoelastic materials. Microstructure analyses of the annealed wires indicate that large Wiedemann twist was attributed to the 〈100〉 circumferential texture and the fcc nanoparticles embedded in bcc matrix. The results indicate that the favorable circumferential texture and heterogeneous structure can be used to guide exploration of materials with large Wiedemann effect. [ABSTRACT FROM AUTHOR]

Grain boundary diffusing process was applied to Nd-Ce-Fe-B sintered magnets using Nd 80- x Dy x Al 20 ( x = 0, 20, 40, 60, 80 at.%) ribbons. After diffusion treatment at 900 °C for 13 h and annealing at 470 °C for 2 h, the coercivities of processed samples were 12.5, 17.2, 14.9, 15.2 and 14.3 kOe, respectively. The highest coercivity, with a 70% increasement compared to original sample, was achieved using Nd 60 Dy 20 Al 20 with the least Dy content. Microstructural investigations show that the coercivity enhancement of these diffused samples is mainly attributed to the magnetic hardening extensive layers along (Nd,Ce) 2 Fe 14 B grains and weakening magnetic coupling between adjacent grains by continuous intergranular phases. Nd 60 Dy 20 Al 20 is a promising diffusion source for producing high-coercivity Nd-Ce-Fe-B sintered magnets with effective Dy utilization. [ABSTRACT FROM AUTHOR]

The paper presented the effect of post-diffusion annealing on the magnetic properties and microstructure of Nd-Fe-B sintered magnets by grain boundary diffusion with Pr 68 Cu 32 , Dy 70 Cu 30 and Pr 35 Dy 35 Cu 30 alloys. The coercivities of the samples changed slightly by diffusing Pr 68 Cu 32 alloy then increased sharply by subsequent post-diffusion annealing. Differently, the coercivities of the samples showed large rise by diffusing Dy 70 Cu 30 and Pr 35 Dy 35 Cu 30 alloys then slight rise by subsequent annealing. Investigation on microstructure revealed that it was mainly due to different mechanism of grain boundary modification by Pr-Cu and Dy-Cu alloys. The coercivity enhancement of the diffused magnets by Dy 70 Cu 30 and Pr 35 Dy 35 Cu 30 alloys was mainly attributed to continuous Dy-rich shells in extensive layers of Nd 2 Fe 14 B grains. Nevertheless, the coercivity enhancement of the diffused magnets by Pr 68 Cu 32 alloy was mainly resulted from relatively continuous and thin intergranular layers isolating Nd 2 Fe 14 B grains, which were achieved only by post-diffusion annealing. [ABSTRACT FROM AUTHOR]

Commercial N50 Nd-Fe-B magnet was processed by grain boundary diffusing Pr-Tb-Cu-Al alloys. The coercivity increased from original 944.9 kA/m to 1640.6 kA/m, 1741.6 kA/m, 1740.2 kA/m and 1775.4 kA/m by diffusing Tb 70 Cu 30 , Pr 52.5 Tb 17.5 Cu 30 , Pr 60 Tb 20 Al 20 and Pr 60 Tb 10 Cu 15 Al 15 alloys, respectively. Microstructural analysis confirmed Tb-rich shells on the surfaces of Nd 2 Fe 14 B grains, contributing to coercivity enhancement of diffused sample. Especially, the partial replacement of Tb by Pr in diffusion sources resulted in higher coercivity by consuming fewer Tb elements, only 0.34–0.53 wt% Tb in the sample by Pr-Tb-Cu-Al, much lower than 1.82 wt% Tb in the sample by Tb-Cu. [ABSTRACT FROM AUTHOR]

[Display omitted] • A double-step diffusion of Pr 60 Cu 20 Al 20 and Tb was applied to the Nd-Fe-B magnet. • Double-step diffusion can increase the diffusion depth of Tb element. • Double-step diffusion can further improve the coercivity of diffused magnets. • Coercivity increased linearly to 21.73 kOe with longer double-step diffusion time. • The layers with anti-core/shell structure were thinner than single-step diffusion. Sintered Nd-Fe-B magnets were processed by single-step diffusion (SSD) with Tb metal and double-step diffusion (DSD) with Pr 60 Cu 20 Al 20 alloy and Tb metal, respectively. The results showed that the coercivity of the magnet increased from 12.87 kOe to 19.01 kOe for SSD and 21.73 kOe for DSD. Moreover, the coercivity of the magnet processed by SSD increased with the increasing diffusion time (t d) to 4 h but hardly changed with further prolongation of t d. However, the coercivity of the DSD magnet increased nearly linearly with increasing t d from 2 h to 8 h. Microstructure analysis showed that the formation of (Nd, Tb) 2 Fe 14 B phases enhanced the coercivity of the SSD and DSD magnets. Tb-poor anti-shells existed in regions near the surfaces of the diffused magnets. However, pre-diffusion of the Pr 60 Cu 20 Al 20 alloy improved the distribution of grain boundary phases in the DSD magnet. The optimized microstructure can promote subsequent Tb diffusion along grain boundaries, resulting in thinner anti-core/shell region layers in the DSD magnet than in the SSD magnet. [ABSTRACT FROM AUTHOR]

The surfaces parallel and perpendicular to c-axis of commercial N52 Nd-Fe-B magnet were coated with Tb by magnetron sputtering, respectively. The effect of Tb diffusion anisotropy on magnetic and mechanical properties was investigated. The coercivity increased from original 13.66 kOe to 21.90 kOe for the magnet diffusing parallel to c-axis and 19.68 kOe for the perpendicular diffusion, mainly resulting from the formation of (Nd, Tb) 2 Fe 14 B shells. The bending strength σ b of original magnet revealed obvious anisotropy. The σ b of diffused magnets for parallel to c-axis and perpendicular to c-axis showed a decrease by 1.76% and 6.14%, respectively. The deterioration in mechanical properties was related to internal stress resulting in transgranular fracture near surface of diffused magnet. The difference of magnetic and mechanical properties for the magnets with diverse diffusion direction was mainly caused by anisotropy of Tb diffusion in magnet. • Tb exhibits obvious anisotropy of diffusion behavior in Nd-Fe-B magnet. • The magnetic and mechanical properties of Tb-diffused magnets are anisotropic. • Internal stress and transgranular fracture near surface change mechanical properties. [ABSTRACT FROM AUTHOR]

• Grain boundary alloying improves the bending strength of sintered Nd-Fe-B magnets. • Internal stress changes the fracture mechanism. • Transgranular fracture is detrimental to bending strength. Commercial Nd-Fe-B sintered magnet was processed by grain boundary diffusing Pr-Cu, Pr-Al, and Pr-Tb-Cu alloys, respectively. The coercivity increased from the original 13.78 kOe to 14.3 kOe, 16.51 kOe and 21.62 kOe, respectively. The bending strength increased from original 290.13 MPa to 315.63 MPa by diffusing Pr-Cu alloy, however, decreased to 266.83 MPa and 268.10 MPa by diffusing Pr-Al and Pr-Tb-Cu alloys, respectively. Microstructure analysis confirmed that Cu was enriched at grain boundaries after diffusion treatment. However, Tb and Al atoms diffused into the main phase and replaced some Nd and Fe atoms. The substitution between atoms results in lattice distortion of main phase, resulting in internal stress, which reduces the bending strength of sintered Nd-Fe-B magnets. [ABSTRACT FROM AUTHOR]

• Nano-TiC particles can significantly improve the bending strength. • Nano-TiC particles are mainly distributed at the triple junction phase. • The complete lattice structure of the nano-TiC particle is maintained. Nano-TiC powder was introduced into sintered Nd-Fe-B magnets and the effect of adding content on mechanical and magnetic properties was investigated. The results show that the bending strength is significantly enhanced, showing an increase of approximately 28% for 0.6 wt% doping magnet compared to the Ref. sample without addition. Meanwhile, the coercivity and squareness degree are enhanced to a certain extent without obvious remanence reduction. Microstructural analysis shows that the nano-TiC particles mainly segregate at triple junction regions, which plays a key role in the enhancement of bending strength. [ABSTRACT FROM AUTHOR]

Abstract: The Tb0.29(Dy1−x Pr x )0.71Fe1.97 (x=0, 0.1, 0.2 and 0.3) alloys were prepared by directional solidification method. The orientation, magnetostriction λ, Curie temperature T c and microstructure of alloys were characterized by XRD, standard resistant strain gauge technique, VSM and SEM-EDS. The results reveal that the alloys have a preferred orientation of 〈110〉 and 〈113〉 direction when x>0. With the increase in Pr content, the T c of alloys decreases gradually and the non-cubic phase appears, resulting in the decline of λ dramatically, from 1935.2×10−6 for x=0 to 695.9×10−6 for x=0.3 at a compressive stress of 6MPa and a magnetic field of H=240kAm−1. [Copyright &y& Elsevier]

[Display omitted] • Coercivity enhancement of Nd-Fe-B magnet was achieved by a combined diffusion. • The combined diffusion method showed effects on improvement of Tb diffusion depth. • Appropriate thick Tb-rich shell around grain was formed in the combined diffusion. • Fewer Tb elements were consumed compared with the conventional diffusion method. • High wettability in boundary was obtained in the first step of combined diffusion. Commercial N50 Nd-Fe-B magnet was processed by a combined diffusion process with Pr 65 Cu 15 Al 20 , followed with Pr 50 Tb 30 Al 20 (at %). The coercivity increment from the original 965.6 kA/m to 1672.5 kA/m was achieved in the combined diffusion sample by introducing 0.23 wt% Tb. However, the coercivity of the conventionally diffused sample with similar Tb content by Pr 50 Tb 30 Al 20 reached only 1386.2 kA/m. Microstructural and compositional analyses revealed that relatively continuous grain boundary phases were first formed in the diffused sample by Pr 65 Cu 15 Al 20 , moreover, appropriate Tb-rich shells around 2:14:1 grains were further formed during the following diffusion by Pr 50 Tb 30 Al 20 alloy. The combined diffusion process was helpful in promoting Tb diffusing along the grain boundary phase and further forming uniform Tb-rich shells. It provided a promising way of accelerating Tb diffusing and enhancing Tb availability. [ABSTRACT FROM AUTHOR]

The fracture mechanism of sintered Nd-Fe-B magnet was analyzed from the perspective of crystallology. The fracture is observed at the interface between the Nd 2 Fe 14 B main phase (MP) and the thin Nd-rich grain boundary phase (TGBP). The determined angle mismatch and lattice mismatch between the MP and TGBP phase indicate an incoherent interface boundary, weakening the binding force between the MP and TGBP. • The fracture site is mainly located at the interface between the main phase and the thin grain boundary phase. • The phase boundary structure between the main phase and grain boundary phase is incoherent phase boundary structure. • The coupling degree between the TGBP and the MP is low. [ABSTRACT FROM AUTHOR]

• Pr-Cu boundary addition was beneficial to the Hcj enhancement of NdFeB magnets. • 4.3 and 6.2 kOe Hcj enhancements were obtained in 5 and 10 wt% Pr-Cu samples. • The Hcj enhancements for Pr-Cu samples were mainly related to the 480 °C annealing. • The micromagnetic parameter α increased from 0.491 to 0.656 after optimal annealing treatment. The annealing effects of NdFeB magnets were usually related to the eutectic liquid segregation from junction to grain boundary regions, atoms solid diffusion at grain boundary regions or structure transition of junction phases. In this work, the microstructure and annealing effects of sintered NdFeB magnets with eutectic Pr-Cu boundary additions (0, 5 and 10 wt%) have been systematically investigated. There were two kinds of boundary phases (Cu-lower phase: fcc REO 2 ; Cu-higher phase: h-RE 2 O 3) in Pr-Cu processed magnets. Pr-Cu showed no positive influence on the coercivity of as-sintered magnets and the first-step annealing at 900 °C followed by quenching was also useless. The best annealing temperature (480 °C) for Pr-Cu processed magnets was slightly higher than the lowest eutectic temperature (476 °C). Microstructural investigations demonstrated that the 480 °C annealing showed no influence on the structure transition of boundary phases but changed their distribution patterns. The dominant annealing effect was the formation of strong exchange-decoupling grain boundary phases (GBPs) which were originated from the eutectic liquid segregation. The repeated heating to 900 °C followed by quenching/furnace cooling for optimal annealed (900 + 480 °C) magnet demonstrated reversible eutectic liquid segregation. Annealing under the lowest eutectic temperature (460 °C) was harmful which indicated that the atoms solid diffusion mechanism was not accessible in Pr-Cu processed magnets. [ABSTRACT FROM AUTHOR]

• The orientation of the magnet is significantly increased by the wet pressing method with special double-layer mold. • The liquid solvents lubricate the powders well and are almost eliminated at the end of the pressing process. • The remanent magnetization of the magnet shows a significant increase with negligible coercivity change. • The density of magnet is greatly increased and approaches the limit one. • The compressive strength of the magnet is greatly improved compared with that of the traditional pressing method. Fine magnetic powder particles are usually utilized to prepare high coercivity Nd-Fe-B magnets. However, it is more difficult to obtain high orientation degree due to the larger friction between finer powder particles during magnetic-aligned compaction process, which greatly affects the performance of final magnets. In this work, a special wet pressing method is adopted to reduce the friction between the powder particles. The degree of alignment of the magnet is obviously increased and the microstructure is optimized. The remanent magnetization of the magnet shows a significant increase with negligible coercivity change, while the compressive strength is improved compared with that of the traditional method. [ABSTRACT FROM AUTHOR]