Unraveling influence of entropy on thermal stability and glass-forming ability of (Fe, Co)-(Ta)-B amorphous alloys: Insights from local atomic structure simulated by ab initio molecular dynamics

The thermal stability, glass-forming ability (GFA), and local atomic structure of (Fe, Co)-(Ta)-B amorphous alloys with different entropy values were investigated by experiments and ab initio molecular dynamics simu-lations, and the effects of entropy were elaborated from the perspective of the local atomic structure. The experimental results show that crystallization temperature, activation energy for crystallization, and under-cooling degree all rise with the increase of configurational entropy (Delta Sconf) of the alloys, whereas the critical thickness for amorphous samples shows a weak correlation with the Delta Sconf. The simulations indicate that the short-range orders of the amorphous alloys are all dominated by B-centered tri-capped trigonal prisms (TTPs) and bi-capped square Archimedean antiprisms, and Fe-/Co-centered deformed body-centered cubic structures (BCCs) and icosahedral-like structures (ICOs) mainly with covalent-like B-Fe/Co and metallic Fe/Co-Fe/Co bonds. The increase in the Delta Sconf results in shortened bond lengths and strengthened interactions between the main atomic pairs and sluggish diffusion of the atoms, thereby leading to enhanced thermal stability of both the amorphous phases and alloy melts. The GFA of the alloys shows a strong correlation with the characteristics of the short-range orders but not the entropy. The alloy containing the lowest fractions of the TTPs and BCCs but considerable ICOs possesses the best GFA.