Unveiling the intrinsic rapid solidification characteristics in B2-ordered multi-principal element intermetallic compounds: Metastability-driven spontaneous grain refinement and performance enhancement

Multi-principal element intermetallic compounds (MPEICs) have garnered significant attention as promising high-temperature structural materials owing to their unique atomic configurations and superior mechanical properties. Despite recent advances, the intrinsic solidification thermodynamics governing the formation of B2-structured MPEICs remains poorly understood, particularly under non-equilibrium conditions. This study presents a pioneering investigation into the rapid solidification pathways of B2-ordered (CoFeNi)₅₀Si₅₀ MPEICs under diverse non-equilibrium conditions. Importantly, the comprehensive experimental characterization and theoretical calculations have confirmed that the dendrite growth of the ordered B2 phase dominantly governs the solidification process, thereby clarifying the mechanisms of spontaneous grain refinement and performance enhancement. With increasing undercooling, the microstructure transformed from typically coarse dendrites to fully refined grains at medium undercooling, primarily attributed to dendrite fragmentation and remelting mechanisms. At high undercooling, stress-induced subgrain-assisted recrystallization became the dominant mechanism for partial grain refinement. The enhanced hardness has been demonstrated to be jointly influenced by two interdependent factors: metastability-driven grain refinement and the accumulation of internal stress. Collectively, this work provides the first comprehensive framework elucidating the intrinsic solidification mechanisms of B2-phase MPEICs, offering critical insights for tailoring microstructure-property relationships in advanced intermetallic systems.