Finite disorder critical point in ductile-to-brittle transition in amorphous solids with aspherical impurities

Enhancing the mechanical strength and stability of amorphous solids is crucial for material design, with microalloying being a common yet poorly understood method. Using molecular dynamics simulations, we investigate the effect of aspherical impurities on the yielding transition of amorphous solids in the context of the ductile-to-brittle transition associated with microalloying. While spherical impurities larger than the constitutive particles lead to a higher yield strain and increased brittleness, we observe that rod-shaped impurities with an aspect ratio slightly larger than one, which introduce rotational degrees of freedom, have a more pronounced effect. As the aspect ratio increases, their rotational freedom is reduced, leading to more brittle yielding. Completely freezing the rotational degrees of freedom can produce both mechanically and kinetically stable amorphous solids that exhibit brittle yielding. Thus, enhancing brittleness through higher fractions of aspherical impurities presents an opportunity to explore the ductile-to-brittle transition, which is easily accessible in experiments, particularly in colloidal systems. Our finite-size scaling analysis provides compelling evidence for the existence of a finite-disorder critical point as the boundary between ductile and brittle yielding. Enhancing the mechanical strength and stability of amorphous solids is crucial for material design, yet the effects of microalloying remain poorly understood. Here, the authors use molecular dynamics simulations to investigate how rod shaped impurities, whose aspect ratio-dependent rotational degrees of freedom influence the yieding behaviour, drive the ductile to brittle transition, and offer insights into designing more stable materials.