Crystallographic alignment of Fe₂B and Nd₂Fe₁₄B for texture memory in hydrogenation–disproportionation–desorption–recombination-processed Nd–Fe–B powders

Texture development in hydrogenation–disproportionation–desorption–recombination (HDDR)-processed NdFeB magnets is discussed with a focus on the crystallographic alignment of the Nd₂Fe₁₄B and Fe₂B phases. By careful control of the dynamic HDDR-processing parameters, shape changes in the HDDR-treated samples were minimized by suitable modifications to the sample dimensions to trace the orientation relation between the c-axes of the Nd₂Fe₁₄B and Fe₂B phases. The magnetic anisotropy was significantly dependent on the hydrogen pressure during the HD process and highly aligned Fe₂B phases, with the same c-axis orientation as the initial Nd₂Fe₁₄B phase, were formed under the dynamic HDDR treatment at a hydrogen pressure of 30 kPa under controlled HD conditions. During the DR reaction following the HD process, the orientation of the initial Nd₂Fe₁₄B was recovered by a highly aligned Fe₂B phase. It was demonstrated that the Fe₂B phase could mediate texture during the HDDR processing owing to the atomic configuration and crystallographic relation between the Nd₂Fe₁₄B and Fe₂B phases.