High-coercivity copper-rich Nd-Fe-B magnets by powder bed fusion using laser beam method
Olivier Tosoni, Elisa Borges Mendonça, Joni Reijonen, Atte Antikainen, Lukas Schäfer, Stefan Riegg, Oliver Gutfleisch
Abstract
Additive manufacturing (AM) is an attractive processing route to make efficient use of rare-earth elements (REE) in systems containing complex-shaped rare-earth (RE) based magnets. Powder bed fusion using laser beam (PBF-LB) is one of the most promising technologies to obtain fully dense AM parts and has seen significant recent research efforts. However, most works use commercial Nd-Fe-B powders with a composition more suited for binder based AM methods, which reduces the 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 having around 30 wt% REE content. 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 Br = 0.62 T, Hcj = 1790 kA.m−1 and BHmax = 65 kJ.m−3 were obtained.