Atomic Mobilities in Liquid and fcc Nd-Fe-B Systems and Their Application in the Design of Quenching Nd₂Fe₁₄B Alloys

Using published and presently calculated diffusivities, a reliable and self-consistent atomic mobility description of the liquid and fcc phases in a Nd-Fe-B system is established by DIffusion-Controlled TRAnsformation software. Based on the obtained atomic mobility-coupled thermodynamic descriptions of the Nd-Fe-B system, a wheel speed-dependent solidification diagram for a model Nd₂Fe₁₄B alloy is constructed, which allows us to examine the influence of wheel speed on the solidification behavior of the quenching Nd₂Fe₁₄B alloy. According to the theoretically obtained solidified microstructures and their relationship with the magnetic properties, the optimal wheel speed when melt-spinning the quenching Nd₂Fe₁₄B ribbons is determined to be 35 m/s. The experimental microstructural characterizations and magnetic hysteresis loop measurements confirm that the ribbon prepared at a wheel speed of 35 m/s exhibits the best comprehensive magnetic properties because the remaining bcc-Fe phase is significantly suppressed and the main Nd₂Fe₁₄B phase was well refined to an ultrafine-grained microstructure. The grain refinement mechanism of the main phase in the ribbons is also described.