Abstract: Nanocomposite permanent magnets have ultra-high theoretical magnetic energy products, due to coupling of the soft/hard magnetic phases, inciting strict microstructural requirements. In this study, the microstructure evolution, including the phase transition, morphological changes, and texture formation, of hot-deformed SmCo-based nanocomposites under thermal-stress-strain coupling was characterized to determine a possible strategy for achieving high performance. The SmCo₅/α-Fe nanocomposites precursor contained fine and dispersed Sm(Fe, Co)₅ and Fe-Co grains and exhibited a two-stage phase transformation accompanied by grain growth. In the early stage of deformation at relatively low temperature, the adjacent Sm(Co, Fe)₅ and Fe-Co phase formed the Sm₂(Co, Fe)₁₇-H phase, which was stable only with small grain sizes. In the high-temperature deformation stage, the Sm₂(Co, Fe)₁₇-H phase transformed into the Sm₂(Co, Fe)₁₇-R phase with large grain sizes. In addition, the strong c-axis texture formed in the Sm(Co, Fe)₅ phase but not in the Sm₂(Co, Fe)₁₇-R phase. Subsequently, the phase transition process and texture formation mechanism were systematically analyzed by transmission electron microscopy. The initiation of a slip system and/or preferential grain growth explained the formation of texture under the action of uniform stress and strain and assisted by dispersed Sm-rich nanograins. The Sm₂(Co, Fe)₁₇-R grains with poor orientations and large grain sizes did not achieve magnetic hardening, which also damage the magnetic properties. According to the results of this work, we also presented a new strategy to prepare high-performance SmCo-based nanocomposites magnets.

Key words: Nanocomposites, Phase transition, Microstructure, C-axis texture, Hot deformation