Unveiling the grain refinement mechanism upon rapid solidification of Ni₇₅Cu₂₅ alloy: A synergistic study of undercooled experiments and MD simulation

Grain refinement of nickel-based high-temperature alloys has perpetually represented a longstanding pursuit within the realm of research. In this study, a synergistic approach combining undercooled experiment and molecular dynamics (MD) simulation was used to unravel the intricate grain refinement mechanism in rapid solidification of Ni₇₅Cu₂₅ alloy. The results show that spontaneous grain refinement occurred at both low and high undercooling. At low undercooling, MD simulations have confirmed that the principal mechanism behind grain refinement is the remelting of primary dendrites. While at the high undercooling, the main mechanisms for grain refinement are the formation of subgrains and subsequent recrystallization. Furthermore, during the transition from low to high undercooling, orientation scattering and orientation splitting caused by subgrain rotation are the common phenomena, leading to the spontaneous grain refinement. The study not only contributes to a better understanding of non-equilibrium solidification phenomena of nickel-based high-temperature alloys but also holds significant implications for tailoring material properties through controlled grain refinement strategies.