Role of Constitutional Supercooling in Grain Refinement Mechanisms of Additively Manufactured Ti–Cu Alloys

Abstract Additively manufactured Ti–8.5Cu alloy has attracted growing interest due to its distinctive microstructure, characterized by fine equiaxed grains and ultra-fine pearlite. However, the primary grain refining mechanism remains unclear due to the formation of pearlite. This study investigates the role of constitutional supercooling (CS) in directed energy deposition—laser beam/metals processed thin-walled Ti–Cu alloys with varying Cu concentrations, by deliberately suppressing pearlite. The absence of pearlite allows for the reconstruction of parent β -Ti grains using the Burgers orientation relationship on electron-backscattered diffraction maps. The results reveal that the CS during solidification, induced by Cu solute addition, significantly refines grains. Additionally, lower laser energy density also promotes grain refinement that can be attributed to the increased thermal undercooling induced by a higher cooling rate. This research quantifies CS under pearlite-suppressed condition to understand its contribution to grain refining mechanisms in Ti–Cu alloys, offering pathways to control the mechanical properties of eutectoid alloy systems. Graphical Abstract