Microstructure-Enhanced Inverse Magnetostrictive Effect in Fe–Co Alloy Wires

Polycrystalline magnetostrictive alloys with a combination of high stiffness and strength and large magnetostriction are desirable for various smart applications, including energy harvesters and microscale sensors and actuators. However, the in-depth understanding of the microstructure–property relationship in these alloys is still limited due to the complexity of their grain geometry, multi-objective design requirements, and the few experimental verifications available. Herein, the correlation between the power generation properties and microstructures controlled by heat treatment in Fe₂₉Co₇₁ (at%) alloys is investigated. As a result, the Fe–Co alloy annealed at 893 K for 5 h, exhibiting fine grains with a {110} <001> orientation, shows excellent characteristics, such as an ultimate tensile strength of 832 MPa, magnetostriction of 117 ppm, and an output voltage density of 130 μV/mm³. The enhancement in power generation performance is due to the increase in magnetostriction, accompanying the refinement of crystal grains by recrystallization. The newly demonstrated linear relationship between grain size and magnetostriction (λ_s = 80.0 D^−1/2 + 133) in this study can be a useful design guideline for further improvement in magnetostrictive materials.