Diffusion Mechanism of Sm and Fe Atoms in Sm<sub>2</sub>Fe<sub>17</sub> Layer in Liquid-solid Diffusion Couple

The Sm₂Fe₁₇ alloy serves as the essential precursor material for the Sm₂Fe₁₇N_{<italic>x</italic>} rare earth permanent magnet. However, the growth mechanism of the Sm₂Fe₁₇ alloy phase remains unclear. In this study, a high-temperature Sm-Fe liquid solid diffusion couple was established to facilitate the growth of a Sm₂Fe₁₇ alloy layer within the temperature range of 1100 ℃ ~1210 ℃. The results indicate that the Fe element within the Fe matrix dissolves rapidly in the Sm melt, leading to the formation of a Sm₂Fe₁₇ alloy layer once the Fe concentration in the Sm-Fe melt reaches a certain threshold. At the same time, it has been observed that the diffusion coefficient of Fe atoms in the Sm₂Fe₁₇ alloy layer is closely related to the square of the growth coefficient of the Sm₂Fe₁₇ alloy layer. This finding confirms that the diffusion rate of Fe in the alloy layer is significantly higher than that of Sm. It also indicates that the growth of the Sm₂Fe₁₇ alloy layer occurs on the side of Sm-Fe melt, suggesting that the diffusion rate of Fe atoms in the alloy layer serves as a rate-limiting factor for Sm₂Fe₁₇ layer growth.