The Contribution of Diffusion Coefficient to the Eutectic Instability and Amorphous Phase Formation

Abstract

The diffusion coefficient D decides the diffusion length of solute boundary and plays a key role in the microstructure selection. This paper examines quantitatively the contribution of diffusion coefficient to the eutectic instability and amorphorization ability. The maximum growth velocity Vmax and the maximum undercooling Tmax as functions of activation energy Q in strong liquids are deduced theoretically based on eutectic growth model by separating Q from D. It reveals that the larger the Q, the smaller the Tmax and Vmax, which shows the same tendency as experimental values in some Al-based alloys and glass formers. This indicates that it is the sluggish movement of atoms that makes the transition from eutectic to others structural morphologies, even to amorphous phase, occur at smaller interface growth velocity or undercooling, which is the main contribution of the diffusion coefficient to the amorphorization ability.