A phase-field study of the peritectic reaction mechanisms in Fe-Ni alloys

Abstract

A quantitative multi-phase field model is used to simulate the peritectic reaction in Fe-Ni alloys at low undercoolings. During the peritectic reaction, the concentration field and growing contour of the γ-phase are utilized to examine the morphological evolution. Numerical simulations indicate that the peritectic reaction contains complex mechanisms that include the remelting of δ-ferrite, the mixing of solutes in the liquid phase, and solute diffusion. It is found that the δ-ferrite remelts near the tip of the advancing γ-platelet during the steady-state peritectic reaction, resulting in the lateral shift of the triple junction. The remelting of δ-ferrite and subsequent solidification of the remelted liquid can contribute to rapid solute mixing in the liquid adjacent to the triple junction and considerably accelerate the growth rate of γ-platelet. The lateral shift of the triple junction can be employed to characterize the simulated morphology of the advancing γ-platelet tip during the Fe-Ni peritectic reaction. A novel Péclet number based on the lateral shift is introduced to quantify the rate of remelting of the δ-ferrite and its impact on the peritectic reaction. The diffusion-controlled mechanism is investigated by the scaling relations between the dimensionless undercooling and the steady-state tip properties, such as the reaction velocity, lateral shift, selection parameter, and Péclet number. The remelting rate of the δ-ferrite, characterized by the new Péclet number for the peritectic reaction, has a major impact on the diffusion-controlled mechanism. The differences in the peritectic morphology of Fe-Ni and Fe-C alloys have been confirmed by comparing the multi-phase field simulations with in-situ investigations. The correlation between the simulated γ-platelet thickness and the in-situ experiment data is considered to be satisfactory.