Strain rate effects on shear-band behavior in the Al-Sm system

Amorphous shear bands that can form in crystalline materials during high-strain-rate deformation are typically precursors to fracture. Since shear bands in crystalline material typically do not persist over a wide range of strain rates, the effect of strain rate on solid-solid phase transformation within shear bands has rarely been discussed. Recent findings reveal that in some materials, shear bands can instead enable plasticity at low strain rates. However, it remains unknown how the mechanics of such shear bands and the resulting mechanical properties depend on the strain rate. Here, the strain-rate dependence of shear bands is investigated in two different compositions of Al-Sm system, where shear bands lead to fracture in one of the compositions and plasticity in the other. We discovered that strain rate directly affects the shear-band density and shear-band behavior, which in turn alters the mechanical properties. In contrast to low strain rates, high strain rates lead to the formation of immature partially amorphous shear bands which then transition into fully amorphous shear bands. The underlying reasons and the mechanisms underlying shear-band formation have been elucidated using a combination of experiments and molecular dynamics simulations across a large range of strain rates.