The growth behavior and kinetics of Nd-Fe intermetallic compounds

Although Nd-Fe intermetallic compounds (IMCs) play an important role in the interfacial phase evolution and microstructure regulation of Nd-Fe-B permanent magnet materials, their diffusion growth behavior and quantitative kinetic parameters remain insufficiently understood. In this work, the growth behavior and kinetics of Nd-Fe intermetallic compounds were systematically investigated using Nd/Fe diffusion couples annealed at 550, 600, and 650 °C. Two stoichiometric intermetallic compounds, Nd₂Fe₁₇ and Nd₅Fe₁₇, were identified as the predominant intermediate phases formed at the bonding interface. The thicknesses of both compounds exhibited clear parabolic relationships with annealing time, indicating diffusion-controlled growth after the initial incubation stage. The corresponding parabolic growth constants were determined, and Arrhenius analysis yielded growth activation energies of 218.83 kJ/mol for Nd₂Fe₁₇ and 284.49 kJ/mol for Nd₅Fe₁₇, indicating that Nd₅Fe₁₇ is more sensitive to temperature than Nd₂Fe₁₇. Furthermore, effective interdiffusion coefficients were evaluated using Wagner's method, and the obtained diffusion activation energies of 218.86 kJ/mol for Nd₂Fe₁₇ and 285.14 kJ/mol for Nd₅Fe₁₇ were in good agreement with those derived from growth kinetics. These results provide quantitative kinetic data and mechanistic insight into the growth of Nd-Fe intermetallic compounds, and offer a useful basis for understanding and controlling interfacial phase evolution in Nd-Fe-B permanent magnet materials.