Multiscale analysis of the effect of competitive nucleation on phase selection in rapid solidification of rare-earth ternary magnetic materials

Rapid solidification of stoichiometric Nd2Fe14B alloy in drop tube processing (DTP) is studied experimentally and theoretically. All relevant physical processes, including fluid flow, heat transfer, nucleation and crystal growth, are modeled at different scales. Transient nucleation is described using an extension of the classical nucleation model in terms of Poisson statistics and accounting for the geometrical factors of heterogeneous nuclei. Analysis of phase selection allows prediction of the appropriate processing conditions to optimize the magnetic properties of the as-solidified Nd–Fe–B samples by reducing the amount of α-Fe that forms during solidification. Comparison with experimental microstructural data confirms the modeling results.