Role of initial solid-liquid interface morphology in governing microstructure evolution of directionally solidified AlCrFeNi3 eutectic high entropy alloys

The influence of initial solid-liquid (S-L) interface morphology on the microstructure evolution of directionally solidified AlCrFeNi3 eutectic high-entropy alloy (EHEA) was systematically investigated. The results show that the initial S-L interfaces at different pulling velocities can be categorized into upper and lower regions. As the pulling velocities increase from 2 µm·s−1 to 100 µm·s−1, the solidified microstructure transforms from fully lamellar to a mixture of lamellar and eutectic colonies, and eventually to entirely eutectic colonies. The critical transformation velocity from fully lamellar to eutectic colony is identified as 10 µm·s−1. At low pulling velocities of 2 µm·s−1 and 5 µm·s−1, the grain growth direction is primarily governed by microstructural heredity from the as-cast state, resulting in a deviation angle between grain growth and the heat flow direction. In contrast, at high pulling velocities of 50 µm·s−1 and 100 µm·s−1, the colonies exhibit a trunk composed of fine layers, with ultra-fine lamellar branches distributed along both sides, and the growth direction is determined by the interplay between heat flow and the initial as-cast microstructure orientation.