Correlation of mechanical properties and electronic structures for NdFeB permanent magnet under hydrostatic pressure based on first-principle calculation

In the present study, the mechanical properties of Nd2Fe14B phase, h-Nd2O3 phase and c-Nd2O3 phase under hydrostatic pressure are calculated by means of first principle based on density functional theory. The results show that Nd2Fe14B phase belongs to a brittle phase, whereas h-Nd2O3 and c-Nd2O3 phases are ductile, where the plasticity of h-Nd2O3 is better than that of c-Nd2O3 phase. Consequently, h-Nd2O3 and c-Nd2O3 phases play an important role in accommodating plastic deformation of NdFeB permanent magnet alloy. Furthermore, the electronic structures of Nd2Fe14B, h-Nd2O3 and c-Nd2O3 phases are calculated based on first principle in order to reveal the mechanisms for the involved mechanical properties. It can be found that according to the electronic structure of Nd2Fe14B phase, the brittleness of Nd2Fe14B phase is attributed to the covalent bonds existing between the B atoms. Under the action of hydrostatic pressure, the charge density of h-Nd2O3 and c-Nd2O3 phases are shifted to the O atoms and simultaneously Nd atoms shall lose the involved electrons. Furthermore, under the action of hydrostatic pressure, h-Nd2O3 phase exhibits decreasing plasticity, but c-Nd2O3 phase presents increasing plasticity, which is attributed to the stronger localization of the electronic structures.