Tailoring Tensile Properties of Al88Ni10MM2 Metallic Glass by In-situ Precipitation of FCC-Al Nanocrystals under Controlled Cooling Rates

Amorphous alloys offer unique opportunities for tailoring microstructures via non-equilibrium processing; however, precise control of nanoscale crystallization during rapid solidification remains challenging without post-solidification heat treatments. Herein, we demonstrate that in-situ precipitation of FCC-Al nanocrystals in an Al 88 Ni 10 MM 2 (MM: Ce-rich misch metal) metallic glass can be effectively controlled solely by tuning the cooling rate during melt-spinning. By systematically varying the wheel speed from 40 m/s to 10 m/s, corresponding to cooling rates from 2.5 × 10⁶ K/s to 4.0 × 10⁵ K/s, we achieve a substantial increase in the number density of FCC-Al nanoprecipitates from 2.15 × 10²¹ to 1.55 × 10²² m⁻³, while maintaining a nearly constant nanocrystal size (∼5–6 nm). To elucidate the governing nucleation kinetics, nucleation delay times were quantified using flash differential scanning calorimetry and employed to construct Time-Temperature-Transformation and Continuous-Cooling-Transformation diagrams. Statistical analysis of nucleation temperatures enables direct estimation of nucleation rates under different cooling conditions, revealing that reduced cooling rates significantly enhance nucleation kinetics, leading to dense in-situ precipitation. In contrast, crystal growth remains strongly diffusion-limited under rapid solidification conditions, thereby constraining precipitate coarsening. Consequently, we establish a cooling-rate-dependent framework for decoupling nucleation and growth during melt-spinning, enabling high-density nanocrystal formation without significant size evolution. Mechanical testing, including ribbon bending and cyclic tensile experiments, confirms that such controlled in-situ nanocrystallization simultaneously enhances both tensile strength and plasticity, addressing one of the long-standing challenges in metallic glass research. This work provides a processing strategy for cooling-driven microstructural design in metallic glasses, offering a pathway to bypass conventional annealing treatments while achieving enhanced mechanical performance.