Magnetic and structural properties of multiple recycled and sustainable sintered Nd-Fe-B magnets

Toward the Improvement of the Short‐Loop Recycling of Dy‐Rich Nd–Fe–B Permanent Magnets: Experimental and Numerical Approaches

“…[ 54,57 ] One reason for these relatively low magnetic performances could be the high level of impurities (C, O, and N) which are known to be detrimental to the magnetic properties. [ 21,72,73 ] No clear difference on the contamination levels was evidenced between the 5 and 3.5 μm batches. We are not in a position to propose an explanation for these a priori surprising results.…”

“…With the standard elaboration process implemented in this study, we manage to fabricate dense magnets with good magnetic properties. It is indeed commonly observed that using recycled materials in such a process can induce a decreased density [8,21,28] due to the incorporation of oxygen and carbon contaminated powders. This drawback is overcome here using only a fraction of recycled powder and a specially designed RE-rich (33.5 wt%) virgin material SC alloy, in order to obtain a sufficient amount of liquid phase during the liquid-phase sintering stage.…”

“…[9][10][11][12][13][14][15][16][17][18] After HD, it is furthermore possible to produce anisotropic sintered magnets by tuning the standard powder metallurgy route. [8,[19][20][21][22][23][24][25][26][27][28][29] Short-loop recycled materials contain impurities, such as C, O, or N, originating from the scrap magnet and hard to remove from the material. [21] To prevent a loss of magnetic properties due to the formation of undesired phases (RE oxides, carbides) and closed porosities after the recycling process, additional elements such as RE hydrides [21,28] or intermetallics [23,25,27] can be mixed with the recycled powder before sintering.…”

“…[8,[19][20][21][22][23][24][25][26][27][28][29] Short-loop recycled materials contain impurities, such as C, O, or N, originating from the scrap magnet and hard to remove from the material. [21] To prevent a loss of magnetic properties due to the formation of undesired phases (RE oxides, carbides) and closed porosities after the recycling process, additional elements such as RE hydrides [21,28] or intermetallics [23,25,27] can be mixed with the recycled powder before sintering. These methods showed promising results even at the industrial scale [25,30] while being as well very energy efficient compared to the elemental recovering of RE.…”

Direct Recycling of Hot‐Deformed Nd–Fe–B Magnet Scrap by Field‐Assisted Sintering Technology

“…Direct alloy techniques of recycling sintered magnets include resintering into a new magnet, melt spinning, HDDR, or recasting into a master alloy. [19][20][21][22] In the case of resintering, unless additional Nd is blended in with the recycled powders, the magnetic properties decrease with each consecutive crushing and recycling of the powders. This is considered to be due to the oxidation of the grain boundary layer, causing it to no longer be able to melt during sintering and form Nd-rich grain boundary phase.…”