Severe plastic deformation of Nd-Fe-B nanocomposite magnets at room temperature

A newly developed isotropic Nd2Fe14B/alpha-Fe nanocomposite magnet was subjected to a series of investigations of its microstructure and magnetic properties. The performance of the optimally annealed sample was found to be H-c = 9.7 kOe and sigma(sat.) = 171 emu/g. Moreover, an attempt was made to produce anisotropic nanocomposite magnets by a high-pressure torsion (HPT) experiment performed at room temperature. The microstructural analyses by TEM in 2D and by FIB-SEM serial sectioning in 3D elucidated that the two-phases microstructure is not distorted homogeneously but shear bands (SBs) are formed. It was found that both the hard magnetic Nd2Fe14B and soft magnetic alpha-Fe phases are distorted significantly near those SBs even though the crystallographic orientations of the Nd2Fe14B grains are randomized therein. The relationships between this microstructure developed by HPT and the corresponding magnetic properties are discussed.