Phase Transformation-Assisted Nucleation and Growth of a Single-Phase FeCoNiCuNb Alloy.

High-entropy alloys utilize high configurational entropy to stabilize solid solutions, suppress intermetallics, and broaden compositional possibilities. However, achieving homogeneity is challenging due to diffusion disparities, especially with refractory metals. Here, a unique kinetic pathway enabling the synthesis of a single-phase FeCoNiCuNb alloy with 8.39 at.% Nb, is reported. In situ transmission electron microscopy heating experiments demonstrate that Cu and Nb exhibit significantly lower propensity to participate in solid solution formation compared to Fe, Co, and Ni. However, suppressing FeCoNi nuclei growth allows Cu/Nb incorporation into an amorphous phase with Fe, Co, and Ni. The nano-sized FeCoNi nucleus undergoes dynamic transitions between crystalline and amorphous states, which increases the vacancy concentration and facilitates Cu and Nb diffusion, ultimately leading to the formation of FeCoNiCuNb nuclei. These phase transitions also enhance crystal growth during Ostwald ripening, ultimately yielding a stable single-phase polycrystalline FeCoNiCuNb alloy. This study highlights unconventional kinetic strategies that expand phase diagram boundaries by leveraging the high-entropy concept.