Nucleation Kinetics in Al-Sm Metallic Glasses

The isothermal nucleation kinetics in Al-Sm metallic glasses with low Sm concentrations (xSm) was studied using molecular dynamics simulations in order to calculate time-temperature-transformation curves. The average delay time of Al nanocrystal nucleation was found to increase exponentially with xSm, whereas the estimated critical cooling rate necessary to avoid crystallization decreases exponentially with xSm. Sm solutes were found to suppress Al nucleation by increasing the attachment barrier and therefore by reducing the attachment frequency. The analysis shows that the attachment of Al to the evolving nucleus has the same characteristics as Al diffusion within the amorphous matrix and they both take place heterogeneously via collective movement of a group of Al atoms.