Microstructural Improvement of NdFeB Magnetic Powders by the Zn Vapor Sorption Treatment

Abstract

The microstructural modification for NdFeB magnetic powders (MQP-B) after Zn vapor sorption has been investigated by transmission electron microscopy (TEM). It is found that a coating layer about 100 nm thick was formed on the surface of powder. Selected area electron diffraction (SAED) pattern and high resolution transmission electron microscopy (HRTEM) analyses show that the coating layer consists of condensed nano-scale crystallites of Fe₁₁Zn₄₀, NdZn₅ and Zn. After the temperature for Zn vapor sorption is raised to 648 K, a thin layer has been formed on boundaries of Nd₂Fe₁₄B grains locally in the rim region of the powders. The morphology of the grain-boundary thin-layers is very similar to that in HDDR-NdFeB magnet powder after Zn vapor sorption treatment. Since the latter has a good thermal stability of magnetic property, the Zn vapor sorption treatment is expected to improve also the thermal stability of MQP-B magnet.