Amorphous shear band formation in elemental β-boron

Abstract

We report the formation of shear-induced amorphization in elemental β‑boron (β-B) using transmission electron microscopy (TEM) and density function theory (DFT) simulations. TEM observations beneath the residual indentation of β-B revealed intragranular nanoscale shear bands along 1¯11¯ and 111 crystallographic planes, which are preceded by nucleation of dislocations. Strain map analyses of the shear band indicated that compressive strain assists in the process of bond breaking and shear strain is involved in the disassembly of icosahedral clusters by forming amorphization within a unit cell of β-B. Further DFT simulations confirmed that the deconstruction of triply fused icosahedral (B28) along 11¯0111slip system in β-B106 has the lowest shear strength leading to the formation of a kink followed by amorphization, which is in line with our experimental observations. This study illustrates the structural evolution of shear amorphization in β-B and provides the basis to improve their mechanical properties through modification of internal structure.