# Interdiffusion and Atomic Mobilities in Rare Earth Alloys: Measurement and Modeling of Dy-Y, Dy-Nd, Sm-Nd, and Sm-Tb Systems

## TL;DR

This paper measures and models atomic diffusion in rare earth alloys, providing new mobility data to improve the design of permanent magnets.

## Contribution

The study provides the first critically evaluated atomic mobility parameters for hcp rare-earth binary systems.

## Key findings

- Interdiffusion coefficients were determined for Dy-Y, Dy-Nd, Sm-Nd, and Sm-Tb systems using EPMA and the Sauer–Freise method.
- Optimized mobility parameters show strong agreement between calculated and experimental diffusion coefficients and concentration profiles.
- The results establish a reliable kinetic database for rare-earth alloys, supporting future multi-component simulations.

## Abstract

Eight diffusion couples were fabricated to systematically investigate the composition-dependent interdiffusion behavior in hcp Dy-Y, Dy-Nd, Sm-Nd, and Sm-Tb binary alloys. The interdiffusion coefficients were determined at two representative temperatures using the Sauer–Freise method based on concentration–distance profiles measured by electron probe microanalysis (EPMA). These experimentally obtained diffusivities, together with available thermodynamic data, were subsequently employed to assess the atomic mobilities of each system by means of the CALTPP (CALculation of Thermo Physical Properties) program within the CALPHAD (CALculation of PHAse Diagrams) framework. The optimized mobility parameters provide a reliable description of the diffusion behavior in all investigated alloys. This reliability is confirmed by the close agreement between the calculated and experimentally measured interdiffusion coefficients, as well as by the strong consistency between the model-predicted and experimental concentration profiles. The present work thus establishes the first set of critically evaluated atomic mobility parameters for these hcp rare-earth binary systems. These results fill an important gap in the kinetic database of rare-earth alloys and lay a robust foundation for future multi-component CALPHAD-based simulations, thereby supporting the design and optimization of advanced rare-earth permanent magnets with improved coercivity and thermal stability.