還元拡散法によるSm-Co磁石合金の生成過程における化学拡散現象

抄録

Diffusion experiments were made by using diffusion couples between Sm and Co metals and Co metal and Co-Sm alloy with liquidus composition to clarify the reaction steps and mechanism occurring in the Reduction-Diffusion Process for making Sm-Co magnet alloys. Microscopic observation and EPMA analysis showed that Sm reacted easily with Co metal to produce liquid Sm-Co alloy, and subsequently diffused into Co metal to form multi-layers of intermetallic compounds such as Sm₂Co₁₇, SmCo₅ and Sm₂Co₇. The thickness of the layer (W) was found to be proportional to the square root of the reaction time (t); W=(kt)^1⁄2, where k is the rate constant of layer growth. The diffusion constant (D in m² s⁻¹) of Sm in a single phase was calculated from the observed values of k to be expressed by D=1.17×10⁻³exp(−265000⁄RT) and D=6.90×10⁻⁵exp(−220000⁄RT) for Sm₂Co₁₇ and SmCo₅, respectively (the activation energy in J/mol).