The Structural Origin of the Amorphous-to-Crystalline Transformation in Cu-Zr Based Amorphous Alloy

Amorphous alloys (AAs) possess a metastable structure from a thermodynamic perspective and tend to crystallize under external conditions, which in turn alters their material properties. To gain an in-depth understanding of their crystallization mechanism, this study employed in situ spherical aberration-corrected transmission electron microscope heating experiments combined with molecular dynamics simulations to reveal the synergistic regulation mechanism between atomic bonding modes and stress distribution during the crystallization of Cu-Zr-based AA. During the heating process, nucleation sites first form inside the amorphous structure and subsequently coalesce to form initial crystalline grains. During crystallization, stress concentrates within the amorphous phase, resulting in intense atomic motion. Meanwhile, the atomic bonding of amorphous phase atoms adjacent to the crystals undergoes significant reorganization, exhibiting a polymorphic transformation involving completely disordered, quasi-ordered, and ordered bonding states. Under the influence of stress, only atoms with ordered bonding are retained. Ultimately, this process reduces the overall disorder of the amorphous structure while enhancing local order, which is macroscopically manifested as the crystallization of the amorphous phase and the growth of grains. This study clarifies the synergistic regulation law of atomic bonding modes and stress distribution on the crystallization behavior of AA at the atomic scale, providing an important theoretical basis for the design of high-performance AAs.