Exploring the influence of anisotropy and microstructure of the sintered Nd-Fe-B magnet using nanoindentation and scratching tests

Abstract

This study evaluated the influence of magnetic anisotropy and microstructure on the mechanical properties and material removal mechanism of anisotropic sintered Nd-Fe-B magnet. Nanoindentation tests were performed to measure the hardness (H), elastic (Es) and shear (G) modulus on two faces and main phases of the Nd-Fe-B material. To understand the contribution of the Nd2Fe14B1 and Nd-rich phases on material removal mechanism, scratching tests were also employed in the present study. Results showed that the Nd-Fe-B exhibits magnetic anisotropy with a high degree of uniaxial texture. Fracture analysis on the parallel and perpendicular faces related to the c-axis revealed no difference in fracture mechanisms. The load-displacement curves indicated that there is similar elastoplastic deformations induced by the penetration of indenter on the analyzed faces. Although Nd-Fe-B exhibits high magnetic anisotropy, the mechanical properties obtained from the two faces studied had not statistic difference. Nd-Fe-B is composed of hard and soft phases, where the Nd2Fe14B1 grain exhibited H = 12.5 ± 0.5 GPa, Es = 191.6 ± 12.6 and G = 77.3 ± 5.1 GPa, whereas the Nd-rich phase had values of H = 6.5 ± 0.7 GPa, Es = 124.0 ± 12.3 GPa and G = 50.0 ± 4.8 GPa. The Nd2Fe14B1 and Nd-rich phases strongly influenced scratch groove formation, being observed intergranular microcrack, replacement of Nd2Fe14B1 grain and bulging of Nd-rich grain boundaries. The mechanical properties of the Nd-Fe-B magnet were not affected by magnetic anisotropy or the high degree of uniaxial texture. However, the Nd2Fe14B1 grain presents higher hardness, elastic and shear modulus than the Nd-rich phase. Such characteristics can affect the machined surface formation when employing abrasive machining processes.