Doping and adsorption mechanism of the element Y modifying the primary Al13Fe4 phase in hypereutectic Al–Fe alloys from first-principles

Abstract

Primary Al₁₃Fe₄ phases tend to grow along the [010] orientation forming coarse needles, flakes and lath shapes in hypereutectic Al–Fe alloys, which seriously deteriorates the mechanical properties of the alloys. Rare earth element modification is an effective method to refine the Al₁₃Fe₄ phase. Herein, the modification mechanism of the element Y on the primary Al₁₃Fe₄ phase was investigated using experimental and theoretical calculations. Addition of 0.5 wt% Y had the best modification effect on the primary Al₁₃Fe₄ phase. Y atoms mainly formed the ternary phase of Al–Fe–Y in the final solidification stage, and no Y element was found in the primary Al₁₃Fe₄ phase, eutectic Al₁₃Fe₄ phase and α-Al phase. Y entered the primary Al₁₃Fe₄ phase and preferably occupied Al sites, but increased the formation enthalpy of Al₁₃Fe₄. When Y atoms substituted the partial sites of Al atoms in the Al₁₃Fe₄ (010) surface, the surface energy reduced and the stability of the (010) surface increased. Therefore, surface doping of Y atoms could slow down the growth rate of the primary Al₁₃Fe₄ phase along the [010] orientation. Furthermore, the adsorption of Y on the (010) surface was an exothermic reaction, in which Y easily adsorbed on the (010) surface. The adsorption of Y changed the (010) surface structure and destroyed the advantage of selective growth along the [010] orientation. Comparatively, the adsorption mechanism was more likely to be the main reason for the morphological modification of the primary Al₁₃Fe₄ phase with the Y element. These calculations revealed the refinement mechanism from a thermodynamic viewpoint.