Laser-beam powder bed fusion of magnetostrictive Fe₈₁Ga₁₉ alloys: parameter optimization, microstructural evolution and magnetostrictive properties

Abstract

Magnetostrictive Fe-Ga alloys, featuring with good machinability, high Curie temperature, and high permeability, have received increasing attention in fields such as actuators, implants, and energy harvesting. Unfortunately, bulk polycrystalline Fe-Ga alloys usually suffer poor magnetostrictive strains compromised by the randomness of grain structure and the intricate phase constitution. The current study was centered on the fabrication of bulk polycrystalline Fe81Ga19 alloys with tailored grain morphology and phase arrangement utilizing laser-beam powder bed fusion (LPBF) technology. Particular emphasis was laid on investigating the repercussions of LPBF process parameters on the microstructure and magnetostrictive performance. The findings illustrated a non-linear interplay between laser power and the relative density of laser powder bed fusion-fabricated (LPBFed) Fe81Ga19 alloys, marked by an initial augmentation followed by a subsequent decrement. Similarly, a consistent trend was observed for the LPBFed alloys at varying scan speeds. In particular, the LPBFed Fe81Ga19 alloys exhibited a highest density at optimized process parameters (laser power set at 120 W paired with a scan speed of 100 mm/s) due to suitable laser energy input during LPBF process. It was experimentally shown that elongated columnar grains and disorder A2 phase structures were obtained within the alloys attibutes to the high temperature gradient and rapid cooling kinetics intrinsic to LPBF, contributing to a desirable magnetostrictive strain of ~87 ppm for bulk polycrystalline Fe81Ga19 alloys. Moreover, a good dynamic magnetostrictive response of the LPBFed alloys was confirmed by the near-synchronous variations between magnetostrictive behavior and alternating magnetic fields. It can be derived from these findings that LPBF process may be a promising method to prepare bulk magnetostrictive Fe-Ga alloys for versatile applications.