Fabrication of crack-free Nd-Fe-B magnets with laser powder bed fusion

Laser powder bed fusion (LPBF) technology is a novel approach for the fabrication of neodymium, iron, and boron (Nd-Fe-B) hard magnets. However, cracks were always observed in the LPBF-fabricated Nd-Fe-B due to the brittle characteristics of the Nd-Fe-B material. This study investigated the mixed powder composition and laser focus position, which were used to prevent cracks on LPBF-fabricated Nd-Fe-B magnets. The Nd-Fe-B magnetic powder (MQP-S) was mixed with low melting point alloy powder (Pr₂₅Nd₇₅)₇₀Cu₃₀. LPBF used to melt and solidify the mixed powder rapidly allows refinement of the grain boundary in the melt pool area. Furthermore, through the defocusing of the laser beam, the melt pool can penetrate a deeper position, and the cracks generated in the previous layers can be remelted. The mixed powder and defocus laser beam produced the maximum magnetic energy of 55.7 kJ/m³ with a crack ratio of 1.05%.