Toward understanding the microstructure characteristics, phase selection and magnetic properties of laser additive manufactured Nd-Fe-B permanent magnets

Abstract

Nd-Fe-B permanent magnets are critical components for energy conversion and electronic devices. The key magnetic properties of Nd-Fe-B magnets, especially the coercivity and remanent magnetization, are strongly dependent on the phase characteristics and microstructure. In this work, Nd-Fe-B magnets were prepared using vacuum induction melting (VIM), laser directed energy deposition (LDED) and laser powder bed fusion (LPBF) technologies. The microstructure evolution and phase selection of Nd-Fe-B magnets were clarified in detail. The results indicated that the solidification velocity (V) and cooling rate (R) are key factors in determining the phase selection. In terms of the VIM-casting Nd-Fe-B magnet, a large volume fraction of the soft magnetic α-Fe phase (39.7 vol.%) and Nd2Fe17Bx metastable phase (34.7 vol.%) are formed due to the low R (2.3×10-1 ℃/s), while the hard magnetic Nd2Fe14B phase is only 5.15 vol.%. With increasing V (<10-2 m/s) and R (5.06×103 ℃/s), part of the soft magnetic α-Fe phase (31.7 vol.%) was suppressed, more Nd2Fe17Bx metastable phases (47.5 vol.%) were formed in the LDED-processed Nd-Fe-B magnet, and the hard magnetic Nd2Fe14B phase also had a low value (3.4 vol.%). As a result, the casting- and LDED-processed Nd-Fe-B magnets exhibit poor magnetic properties. In contrast, the high V (>10-2 m/s) and R (1.45×106 ℃/s) led to the formation of the hard magnetic Nd2Fe14B phase (55.8 vol.%) from liquid, and the α-Fe phase and Nd2Fe17Bx phase precipitation were suppressed in the LPBF-processed Nd-Fe-B magnet. Furthermore, the strong crystallographic texture on the {001} crystal plane is another reason for the remanence enhancement in the LPBF-processed Nd-Fe-B magnets. Consequently, a coercivity of 656 kA/m, a remanence of 0.79 T and maximum energy product of 71.5 kJ/m3 was achieved in the LPBF-processed Nd-Fe-B magnet, which indicated excellent magnetic performance, comparable to other additive manufacturing processed Nd-Fe-B magnets from MQP (Nd-lean) Nd-Fe-B powder.

Effect of Magnetic Moment on Carrier Effective Mass and Transport in Magnetic Nd2Fe14B Composite Bi2Te3 Films

“…Phase compositions analyzed by using XRD are shown in Figure e. Comparing with the standard peaks of Bi 2 Te 3 (JCPDS: 15-0863) and Nd 2 Fe 14 B (JCPDS: 36-1296), structures of both Bi 2 Te 3 and Nd 2 Fe 14 B are polycrystalline. The Nd 2 Fe 14 B phase content is about 27.93%.…”

Recent innovations in laser additive manufacturing of titanium alloys

“…In recent years, additive manufacturing (AM) is leading a revolutionary change due to its capability to produce near-netshape complex geometry components from 3D models to 3D parts [2][3][4]. Thus, machining can be largely avoided or considerably reduced, significantly improving the material utilization rate.…”