Unveiling the mechanism of phase and morphology selections during the devitrification of Al-Sm amorphous ribbon

The complex interplay between energetic and kinetic factors that governs the phase and morphology selections can originate at the earliest stage of crystallization in the amorphous parent phases. Because of the extreme difficulties in capturing the microscopic nucleation process, a detailed picture of how initial disordered structures affect the transformation pathway remains unclear. Here, we report the experimental observation of widely varying phase selection and grain size evolution during the devitrification of a homogeneous melt-spun glassy ribbon. Two different crystalline phases theta-Al5Sm and epsilon-Al60Sm11 are found to form in the different regions of the same metallic glass (MG) ribbon during the devitrification. The grain size of the epsilon-Al60Sm11 phase shows a strong spatial heterogeneity. The coarse-grained epsilon-Al60Sm11 phase coupled with the small volume fraction of the theta-Al5Sm phase is preferably formed close to the wheel side of the melt-spun ribbon. Combining experimental characterization and computational simulations, we show that phase selection and microstructure evolution can be traced back to different types and populations of atomic clusters that serve as precursors for the nucleation of different crystalline phases. Inhomogeneous cooling rates cause different structure orders across the glass sample during the quenching process. Our findings provide direct insight into the effect of structural order on the crystallization pathways during the devitrification of MG. It also opens an avenue to study the detailed nucleation process at the atomic level using the MG as a platform and suggests the opportunity of microstructure and property design via controlling the cooling process.

Automated summary

This study observed the experimental phenomena of phase selection and grain size evolution during the devitrification of a homogeneous melt-spun glassy ribbon, finding different crystalline phases and grain size distributions. The research revealed that different types and populations of atomic clusters can influence the nucleation of different crystalline phases, and that uneven cooling rates lead to different structural orderings within the glass sample.