Phase‐Resolved Defect Transport Mechanisms Governing Asynchronous Ordering in a Eutectic High‐Entropy Alloy

ABSTRACT Eutectic high‐entropy alloys (EHEAs) exhibit asynchronous phase evolution under identical thermal conditions, yet the underlying mechanisms remain unclear. Here, we investigated the isothermal annealing of AlCoCrCuFeNi alloy using phase‐resolved experiments and atomistic simulations. Electron microscopy revealed sharply contrasting structural pathways: the initially disordered BCC‐FeCr phase progressively developed long‐range order, whereas the B2‐NiAl phase retained its macroscopically ordered framework while undergoing local structural relaxation. Molecular dynamics and Monte Carlo simulations traced this discrepancy to phase‐dependent defect energetics. In B2‐NiAl, low vacancy formation and migration energies enable efficient vacancy‐mediated transport, promoting local structural refinement without disrupting the ordered lattice. In BCC‐FeCr, constrained vacancy transport together with accessible low‐energy interstitial configurations gives rise to a cooperative vacancy‐interstitial transport mechanism required for the disorder‐to‐order transition. These heterogeneous defect transport mechanisms govern asynchronous ordering in EHEAs and provide a phase‐resolved basis for designing thermally stable complex alloys.