Development Of Phase Diagrams For The Design Of HDDR Cycles To Induce Anisotropy In Recycled Gas Atomized Nd-Fe-B Powders

Authors: Diego Monzón Martín (CEIT-BRTA, Spain) Gabriela Sarriegui (CEIT-BRTA, Spain) Pablo Ortega (CEIT-BRTA, Spain) Nerea Burgos (CEIT-BRTA, Spain) José Manuel Martín (CEIT-BRTA, Spain) Valentina Zhukova (UPV|EHU, Spain) Arkady Zhukov (UPV|EHU, Spain) Abstract: This work proposes hydrogenation–disproportionation–desorption–recombination (HDDR) as an effective process to induce anisotropy in recycled gas‑atomized Nd‑Fe‑B powders. It introduces a systematic approach to tailor the cycles according to the composition by using phase diagrams. The method accounts for variations in the recovered material and for the sensitivity of the HDDR parameters to alloying elements, allowing a design of the cycle linked to the phase transition. Magnets scrap was gas-atomized into spherical powders, producing and characterizing four different compositions. To construct phase diagrams, differential scanning calorimetry (DSC) at different hydrogen partial pressures was used. HDDR cycles were then designed based on these diagrams. After heat treatment, the microstructure and magnetic properties of the resulting powders were evaluated. Adapting the HDDR cycle to the specific composition enables controlled grain refinement and anisotropy development, improving the powder magnetic performance and its suitability for bonded magnet manufacturing. DOI: https://doi.org/10.59499/EP267157396