Effect of desorption and recombination on texture development in hydrogenation–disproportionation–desorption–recombination processed Nd–Fe–B magnets

The microstructural evolution of Nd–Fe–B magnets during a hydrogenation–disproportionation–desorption–recombination (HDDR) process was investigated, with particular focus on the effects of the desorption–recombination (DR) stage of the process. Samples that went through the DR process under different conditions were compared to examine the texture development during the reaction. Even though the same hydrogenation–disproportionation (HD) treatment was carried out on all samples before the DR reaction, variations in conditions of the latter significantly affected the development of texture in the samples. In consideration of the microstructural evolution, magnetic properties, and thermodynamics, nucleation of recombined Nd₂Fe₁₄B grains was found to occur not only at the NdH₂/Fe₂B interfaces but also at the NdH₂/α-Fe interfaces, and it was affected by the desorption of hydrogen. Preferential growth of nuclei at the NdH₂/Fe₂B interfaces, which led to a highly textured Nd₂Fe₁₄B phase, could be induced by slow desorption and recombination with a low driving force. Hydrogen desorption at a slower rate was important for achieving high magnetic anisotropy in the HDDR-processed Nd–Fe–B powders.