| Popis: |
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. |
