“…6 , left image). This is an artefact common to materials made from melt spun ribbons 37 . Figure 6 Typical SEM secondary electron images of the fracture surface of the commercial MQIII-F material.…”
In the drive to reduce the critical Heavy Rare Earth (HRE) content of magnets for green technologies, HRE-free Nd-Fe-B has become an attractive option. HRE is added to Nd-Fe-B to enhance the high temperature performance of the magnets. To produce similar high temperature properties without HRE, a crystallographically textured nanoscale grain structure is ideal; and this conventionally requires expensive “die upset” processing routes. Here, a Flash Spark Plasma Sintering (FSPS) process has been applied to a Dy-free Nd30.0Fe61.8Co5.8Ga0.6Al0.1B0.9 melt spun powder (MQU-F, neo Magnequench). Rapid sinter-forging of a green compact to near theoretical density was achieved during the 10 s process, and therefore represents a quick and efficient means of producing die-upset Nd-Fe-B material. The microstructure of the FSPS samples was investigated by SEM and TEM imaging, and the observations were used to guide the optimisation of the process. The most optimal sample is compared directly to commercially die-upset forged (MQIII-F) material made from the same MQU-F powder. It is shown that the grain size of the FSPS material is halved in comparison to the MQIII-F material, leading to a 14% increase in coercivity (1438 kA m−1) and matched remanence (1.16 T) giving a BHmax of 230 kJ m−3.
“…6 , left image). This is an artefact common to materials made from melt spun ribbons 37 . Figure 6 Typical SEM secondary electron images of the fracture surface of the commercial MQIII-F material.…”
In the drive to reduce the critical Heavy Rare Earth (HRE) content of magnets for green technologies, HRE-free Nd-Fe-B has become an attractive option. HRE is added to Nd-Fe-B to enhance the high temperature performance of the magnets. To produce similar high temperature properties without HRE, a crystallographically textured nanoscale grain structure is ideal; and this conventionally requires expensive “die upset” processing routes. Here, a Flash Spark Plasma Sintering (FSPS) process has been applied to a Dy-free Nd30.0Fe61.8Co5.8Ga0.6Al0.1B0.9 melt spun powder (MQU-F, neo Magnequench). Rapid sinter-forging of a green compact to near theoretical density was achieved during the 10 s process, and therefore represents a quick and efficient means of producing die-upset Nd-Fe-B material. The microstructure of the FSPS samples was investigated by SEM and TEM imaging, and the observations were used to guide the optimisation of the process. The most optimal sample is compared directly to commercially die-upset forged (MQIII-F) material made from the same MQU-F powder. It is shown that the grain size of the FSPS material is halved in comparison to the MQIII-F material, leading to a 14% increase in coercivity (1438 kA m−1) and matched remanence (1.16 T) giving a BHmax of 230 kJ m−3.
“…al. [4] investigated the influence of the Nd content on the microstructure and magnetic properties of hot deformed magnets with nominal composition Nd 12.8+x Fe 75.28−x Co 5.5 Ga 0.42 B 6 , as shown in Figs. 11 and 12.…”
Section: Influence Of Chemical Compositionmentioning
confidence: 99%
“…Tang et al [26] increased the coercivity of the Nd-Fe-B hot-deformed magnet from 15.0 kOe to 22.7 kOe by the addition of Dy-based meltspun powders. [4] It has been reported that coercivity and maximum energy product are enhanced significantly by the addition of Cu powder using dual-alloy technology. [14] Microstructure analyses indicate that the NdCu 2 phase is formed in grain boundaries, which obviously improves the texture of the Cu-doped magnet due to the lower melting point of the intergranular phase.…”
Section: Influence Of Chemical Compositionmentioning
confidence: 99%
“…The grains, whose c-axes form smaller angles with the press direction, can more easily devour the misoriented grains via the precipitation growth or diffusion slip processes, because the strain energy of the misoriented grains is much higher than that of the well-aligned grains. [3,4] The preferred growth and rotation of the grains may be simultaneous, or more likely, they dominate in different steps in the texture formation process. As a special example, the radial alignment for the back extruded ring magnet is obtained via the platelet-shaped grain rotation or alignment in the extrusion process, and these grains are formed before extrusion.…”
Hot deformation is one of the primary methods for fabricating anisotropic rare earth permanent magnets. Firstly, rapidly quenched powder flakes with a nanocrystal structure are condensed into fully dense isotropic precursors using the hot-pressing process. The prepared isotropic precursors are then hot-deformed to produce high-anisotropy uniaxial bulk rare earth permanent magnets and a highly textured structure is produced via this process. The resulting magnets possess many advantages such as near-net-shape, outstanding corrosion resistance, and ultrafine-grain structure. The influence of the preparation parameters utilized in the hot-pressing and deformation processes on the magnetic properties and microstructure of the permanent magnets are systemically summarized in this report. As a near-net-shape technique, the hot deformation process has notable advantages with regard to the production of irregular shapes, especially for radially oriented ringshaped magnets with high length-diameter ratios or thin walls. The difficulties associated with the fabrication of crack-free, homogeneous, and non-decentered ring-shaped magnets are substantially resolved through an emphasis on mold design, adjustment of deformation parameters, and application of theoretical simulation. Considering the characteristics of hotdeformed magnets which include grain shape and size, anisotropic distribution of intergranular phases, etc., investigation and improvement of the mechanical and electric properties, in addition to thermal stability, with the objective of improving the application of hot-deformed magnets or ring-shaped magnets, is of practical significance.
“…The maximum energy product is up to 54.4 MGOe [1][2][3]. The optimally quenched melt-spun ribbons have equiaxed and randomly oriented Nd 2 Fe 14 B grains.…”
Nd-Fe-B high performance magnets were prepared by die-upset forging. The effects of the deformation parameters on magnetic properties and flow stress were studied. Deformation temperatures in the range of 600~900 o C enable to achieve an effective anisotropy and temperature 800 o C proves to be suitable for deformation of Nd-Fe-B magnets. The amount of c-axis alignment along the press direction seems to depend on the amount of deformation and a saturation behavior is shown at deformation ratio of 75%. Magnetic properties are also related to strain rate, and maximum energy product is attained at an optimum strain rate of = 1 × 10. By analyzing the relationship of stress and strain at different deformation temperature during die-upset forging process, deformation behavior of Nd-Fe-B magnets was studied and parameters for describing plastic deformation were obtained. Nd-rich boundary liquid phase, which is additionally decreasing the flow stress during deformation, is supposed to play the role of diffusion path and enhance the diffusion rate.
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