High-coercivity copper-rich Nd-Fe-B magnets by powder bed fusion using laser beam method
Résumé
Additive manufacturing (AM) is an attractive processing route to make efficient use of rare-earths in systems containing complex-shaped rare-earth based magnets. Powder bed fusion using laser beam (PBF-LB) is one of the most promising technologies to obtain fully dense printed parts and has seen significant recent research. However, most works use commercial NdFeB-type powders with a composition more suited for binder based AM methods, which reduces the printing parameter window and does not allow property enhancement by the application of annealing cycles. In this work, a close-to-industrial process route was developed in order to produce a narrow-distributed 40-µm Nd-Fe-B powder, derived from strip casting, hydrogen decrepitation and milling, with a composition close to the usual sintered magnet grades. The composition was adjusted by preliminary small-scale experiments focused on the reduction of cracking and the promotion of fine-grained equiaxed microstructures. This powder was then used to build magnets by the PBF-LB method. The best magnetic properties could be achieved with building conditions providing just enough energy to completely melt the material, yielding nano-grained microstructures almost deprived of α-Fe phase. After laser parameter optimization and post-process annealing, properties of B$_r$ = 0.62T, H$_{cj}$ = 1790 kA.m$^{-1}$ and BH$_{max}$ = 65 kJ.m$^{-3}$ were obtained.
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