Design and Qualification of Pr–Fe–Cu–B Alloys for the Additive Manufacturing of Permanent Magnets

Abstract

The direct use of an advanced binder‐free additive manufacturing technique, namely laser powder bed fusion (L‐PBF), does not easily allow obtaining variously shaped, fully dense Nd–Fe–B magnets with high coercivity. The process inherently leads to the re‐melting of the powder and appearance/disappearance of undesired/desired microstructural features responsible for low and large coercivity. In this work, the development of a useful microstructure responsible for high coercivity in Pr21Fe73.5Cu2B3.5 and Nd21Fe73.5Cu2B3.5 alloys and a possible way to produce fully dense permanent magnets via additive manufacturing processes is demonstrated using: (i) suction casting technique, which provides a high cooling rate and thus similar microstructures as in L‐PBF but requires only very small amounts of powder; (ii) conventional L‐PBF processing using kg of powder, and (iii) a subsequent annealing treatment that is similar to a conventional sintering treatment. The subsequent heat treatment is necessary to develop high coercivity by forming a novel microstructure: hard magnetic (Nd,Pr)2Fe14B grains embedded in a matrix of intermetallic (Nd,Pr)6Fe13Cu phase. Furthermore, it is demonstrated that Pr21Fe73.5Cu2B3.5 exhibits a higher coercivity than Nd21Fe73.5Cu2B3.5 because of a finer and more homogeneous grain size distribution of the Pr2Fe14B phase. The final L‐PBF printed Pr21Fe73.5Cu2B3.5 samples provide a coercivity of 0.75 T.

Additive Manufacturing of Textured FePrCuB Permanent Magnets

“…In the case of L-PBF, the axis in the build direction has the highest cooling rate The magnetic properties obtained for annealed BMC material are in good agreement with the magnetic properties obtained in the literature for cast material [16,17]. The brief trial of laser melting a few powder layers of Fe73.5-Pr21.0-Cu2.0-B3.5 as reported in [26] resulted in a coercive field of 0.75 T and remanence of 38 Am/kg. Assuming a density of 7.4 g/cm 3 , the remanence value is equivalent to 0.35 T.…”

“…The best magnetic properties reported so far for as-cast material were obtained for the chemical composition Fe73.8-Pr20.5-Cu2.0-B3.7 and two-step heat treatment (step 1: 1000 • C/5 h; step 2: 500 • C/3 h) yielding J r = 0.62 T, µ 0 H c = 1.13 T and (BH) max = 70.0 kJ/m 3 [17]. Recently, limited trials of laser melting for a few powder layers of a similar composition (Fe73.5-Pr21.0-Cu2.0-B3.5) resulted in very small samples showing a remanence of J r = 38 Am/kg and a coercive field of µ 0 H c = 0.75 T [26].…”

The Magnetic Properties of a NdFeB Permanent Magnets Prepared by Selective Laser Sintering

“…The general possibility of obtaining the anisotropy of magnetic properties of printed magnets via the formation of a temperature gradient was shown in [17]. An original approach to fast searching for the compositions for the 3D printing and estimation of potential magnetic properties was given in [18]. In recent years, there is a direction of studies related to the formation of microstructural peculiarities [19] and cracks in magnets [20].…”

Structure and Magnetic Properties of Intermetallic Rare-Earth-Transition-Metal Compounds: A Review

“…The microstructure must allow reaching the highest possible coercivity and remanent induction and a magnetization loop close to a rectangular one. The achievement of each of these objectives is facilitated by the existence of a granular microstructure [ 2 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ].…”