Atomic-scale mechanisms of stress-controlled nanocrystal nucleation in amorphous alloys

Stress annealing offers a powerful route to control nanocrystallization in amorphous alloys, yet the atomic-scale mechanisms remain poorly understood. Here, we reveal that tensile stress significantly increases the density of preordered Cu clusters and induces their anisotropic alignment along the stress direction. These clusters act as preferential nucleation sites for Fe–Si nanocrystals, promoting directional growth and resulting in pronounced structural anisotropy. In the stress-annealed samples, the parallel-to-perpendicular cluster orientation ratio reaches 1.86, confirming the strong directional influence of applied stress. This stress-mediated enhancement of nucleation, coupled with suppression of isotropic crystal growth, leads to refined grains and controllable nanocrystallization pathways. These results provide critical atomic-scale insights into stress-directed microstructural evolution and establish a fundamental basis for engineering the nanocrystallization of amorphous alloys through stress-based processing.