Dynamic observation on microstructure of the B-rich and Nd2Fe14B phases in Nd-Fe-B alloy by means of HVEM and Mössbauer effect analysis

Abstract

The B-rich phase in Nd-Fe-B magnet was studied by means of HVEM, Mossbauer spectroscopy, X-ray diffraction and magnetic measurements. It can be represented by chemical formula Nd1+eFe4B4 with ɛ, which is about 0.1. High density planar defects were observed in the B-rich phase. X-ray diffraction and electron diffraction show that Nd1+eFe4B4 compound is composed of two interpenetrating subsystems which both belong to tetragonal symmetry. The compound may be the compositional incommensurate structure in c direction. As Nd-Fe-B magnet is heated to 322 °C, the lattice of the B-rich phase is distorted and the remarkable change in microstructure can be observed. However, the microstructure of the B-rich phase at 500 °C was similar to that at room temperature. The Mossbauer investigation and magnetic measurements indicate that the B-rich phase is paramagnetic at room temperature, so it may behave as nonmagnetic inclusion to improve coercivity of the Nd-Fe-B magnet. By analysis on Mossbauer effect to Nd15Fe85−xBx (x = 0, 4, 8, 11) it follows that boron (B) content increase, Nd2Fe14B magnetism look gradually increase in alloy, As x < 4, there are no rich boron look appearance, and Nd2Fe14B descends 24%, magnet performance descends too. If x = 11, Nd2Fe14B descends 5%. It does not affect intrinsic coercivity, but enhance, Nd2Fe14B quantity and the saturation magnetization intension, properly controling boron (B) content and alloy ingredient, properly increasing Fe enhance Nd2Fe14B comprehensive effective.