Laser-beam powder bed fusion and post-build annealing of polycrystalline Fe81Ga19 alloys: Microstructure manipulation and magnetostrictive properties

Abstract

Magnetostrictive polycrystalline Fe-Ga alloys are gaining increasing attention for boarder practicalities, unfortunately, always facing limitations in magnetostrictive properties hindered by random grain structure and complex phase composition. In this work, an innovative method was established to fabricate massive polycrystalline Fe₈₁Ga₁₉ alloys via laser-beam powder bed fusion (LPBF) followed by post-build annealing treatment, and the magnetostrictive performances of the LPBF-fabricated Fe-Ga alloys annealed at various temperatures (800, 1000, and 1200 °C) were systematically investigated. Microstructural analyses revealed that <001> grain orientation and disordered A2 structure were obtained within the LPBF-fabricated (LPBFed) Fe₈₁Ga₁₉ alloys as a result of the steep temperature gradient and rapid solidification. Furthermore, the post-LPBF annealing treatment promoted the grain growth and release of residual stresses, simultaneously accompanied by intensified oriented texture within the annealed alloys. As a result, the Fe₈₁Ga₁₉ alloy annealed at 1200 °C showed optimal magnetostrictive performances with a magnetostrictive strain of ∼70 ppm and especially a 64 % reduction in saturation field relative to the LPBFed alloy. Moreover, the prepared Fe-Ga alloys also manifested good magnetostrictive dynamic response and desirable soft magnetic properties. In addition, electrochemical tests also indicated accelerated corrosion for the annealed alloys owing to the increased grain sizes. This work may pave a processing base to fabricate structure-tailored polycrystalline magnetostrictive Fe-Ga alloys for diverse applications.