Thermal expansion behavior of sintered Nd–Fe–B magnets with different Co contents and orientations

Abstract

The thermal expansion behavior of sintered Nd–Fe–B magnets is a crucial parameter for production and application. However, this aspect has not been thoroughly investigated. In this study, three different sintered Nd–Fe–B magnets with varying Co content (Co = 0, 6, 12 wt%) were prepared using the conventional powder metallurgy method, and four magnets oriented under different magnetic fields were prepared to compare. The thermal expansion behavior for the magnets was investigated using a linear thermal dilatometry in the temperature range of 20 °C–500 °C. It was found that, the coefficient of thermal expansion (CTE) increases with the increase of Co contents, while the anisotropy of thermal expansion decreases. The introduction of Co leads to continuous changes from negative to positive thermal expansion in the vertically oriented direction, which is important for the development of zero thermal expansion magnets. The thermal expansion of non-oriented magnets was found to be isotropic. Additionally, the anisotropy of thermal expansion increases with the increase of orientation degree. These results have important implications for the development of sintered Nd–Fe–B with controllable CTE.