Effects of excessive grain growth on the magnetic and mechanical properties of hot-deformed NdFeB magnets

The magnetic and mechanical properties of rare-earth magnets hot-deformed at temperature range 750–950 °C have been investigated. The grains tended to grow excessively from dozens of nanometers to several microns at the temperatures above 850 °C. The alignment of grains was disrupted by the hot deformation at the high temperatures. The Nd-rich phase was extruded at the temperatures which are higher than 850 °C. The Nd-rich phase extrusion resulted in the reduction of density by 1% and the reduction of remanence from 1.42 to 0.72 T. The reduction of grain boundaries caused by flat platelet-shaped grains changing to spherical grains and the weak binding strength among large grains of Nd2Fe14B phase may be the main reasons for the low mechanical strength of hot-deformed magnets.