Abstract
? 2022 Elsevier B.V.It is challenging to simultaneously improve the coercivity, remanence and squareness factors of sintered and hot-deformed magnets, because of the complicated influences by various microstructure factors. In this work, we demonstrate that the coercivity, remanence and squareness factor of hot-deformed Nd-Fe-B magnet can be enhanced simultaneously by high-temperature short-term annealing process. The coercivity of the hot-deformed sample increased from 1.05 T to a maximum of 1.28 T after annealing at 800 °C, and decreased to 0.87 T at 900 °C. The remanence of the hot-deformed sample increased continuously from 1.41 to 1.49 T as the annealing temperature increased to 900 °C. The calculated squareness value firstly increased from 0.91 to 0.97 at 850 °C, then decreased to 0.74 at 900 °C. An block-shaped Nd-Fe-rich phase, Nd6(Fe,Co)13Ga, was identified in hot-deformed sample. The improvement of coercivity is due to the melting and infiltration of Nd6(Fe,Co)13Ga phase from the surface of powder flakes into the grain boundaries during annealing process. The slightly anisotropic growth of Nd2Fe14B grains results in an improved grain alignment thus the enhanced remanence. Furthermore, the melting point of Nd6Fe13Ga (810 ℃) and Nd6(Fe,Co)13Ga (760 ℃) phases were confirmed by DSC, indicates that adding a small amount of Co element in Nd6Fe13Ga compound can significantly reduce its melting point. Due to the micrometer scale infiltration distance from powder flake surface into the grain boundaries, a balance between infiltration within the powder flakes and grain growth can be achieved under the present processing conditions. This opens up a new route to improve the coercivity, remanence and squareness factor simultaneously for hot-deformed Nd-Fe-B sample.
NSTL
Elsevier