In situ dynamic observation and Mössbauer effect of microstructure of sintered Nd16Fe69Co8B7 magnet

Abstract

In this paper the in situ dynamic observation of microstructure characterization of sintered Nd16Fe69Co8B7 magnet was carried out by using a high voltage electron microscope. At room temperature a number of spherical Nd2O3 inclusions are found to be embeded in some Nd2 (Fe,Co)14B grains. When temperature reaches to 400 °C, a few of small precipitates occur in the matrix, the precipitates grow up and are needle-like. With the temperature increasing to 500 °C, precipitates occur in the matrix. In addition, the Nd-rich phase and other undetermined phase are found in the grain boundary with increasing of temperature, remarkable change is not found for the Nd-rich grain boundary phase. When temperature reaches to 700 °C, a structure transition seems to take place in the undetermined grain boundary phase. Co underlying take up j2 crystal increase exchange function. Its result lead to increasement of Curie temperature TC. The j2 site has very strong face anisotropy, Co atom underlyings replacing Fe strengthens anisotropy. When Co content increases, the tetragonal phase Nd2 (Fe1−xCox)B uniaxial anisotropy is attenuated, besides as Co content increase, soft magnetism Nd(Co, Fe) appears. Therefore, as Co content increases, coercivity rapidly descended.