Distinct difference between peri-eutectic and eutectic growth in ternary Fe-Ni-Ti alloy

Peri-eutectic transition L+δ-Fe→γ-Fe(Ni)+Fe₂Ti in ternary Fe_66.5Ni_17.6Ti_15.9 alloy was investigated using directional solidification technique. We found that the primary phase and the peri‑eutectic in the solid region had a common orientation relationship, while the eutectic in the mushy zone had multiple orientation relationships. This firstly provided the evidence for the different growth mechanisms of peri-eutectic and eutectic, and secondly clarified that the peri‑eutectic nucleated from the primary phase and grew cooperatively. These orientation relationships related with interface structure and solidification kinetics. The peri‑eutectic had complicated interface structure characterized by a quaternary junction and grew under near equilibrium, whereas the eutectic had fewer interfaces and formed during quenching. Besides, the primary δ-Fe phase transformed to the lamellar α-Fe phase with different orientations after peri‑eutectic transition. This work is helpful for further understanding the peri‑eutectic transition as well as the connection between growth mechanism and crystallographic orientation in ternary alloys.