Defect-structure-property relationships in laser powder bed fusion processed NdFeB magnets: The dominant role of laser energy density

Abstract

This study investigates the challenges of microstructure control and defect mitigation in the fabrication of NdFeB permanent magnets via laser powder bed fusion (LPBF), systematically elucidating the influence of laser energy density on densification behavior, microstructural evolution, and magnetic properties. Experimental results demonstrate that increasing laser energy density under appropriate power levels enhances the relative density of samples to 95.8 %. However, excessive or insufficient power triggers vertical wide cracks, attributed to the synergistic effects of gradient thermal stress concentration, Nd-rich liquid film-induced grain boundary weakening, and insufficient volumetric melt feeding rate to compensate for solidification shrinkage and thermal deformation during solidification. Microstructural analysis reveals that the melt pool's rapid cooling rate promotes an increase in the volume fraction of the Nd₂Fe₁₄B main phase to 78.5 %, resulting in a 3.28-fold enhancement in magnetic energy product compared to samples produced by conventional processes. Electron backscatter diffraction characterization indicates a preferential < 001 > orientation along the laser scanning direction, yielding a 16.4 % higher magnetic energy product than that along the build direction. By establishing the multi-scale correlation of process parameters, microstructure, and magnetic properties, this research clarifies the mechanisms of crack initiation and propagation and the principles of magnetic performance regulation for developing high-performance additively manufactured permanent magnets.