Mitigating amorphization in superhard boron carbide by microalloying-induced stacking fault formation

The abnormal brittle failure of superhard boron carbide $({\mathrm{B}}_{4}\mathrm{C})$ and other icosahedral solids arises from the shear-induced amorphization. Mitigating the amorphization in these materials remains challenging due to the lack of other deformation mechanisms such as mobile dislocations. This paper illustrates the shear-induced amorphization process of ${\mathrm{B}}_{4}\mathrm{C}$ from molecular dynamics (MD) simulations using quantum-mechanics-derived machine-learning force field. The amorphization in ${\mathrm{B}}_{4}\mathrm{C}$ initiates from the disintegration of icosahedral clusters, and then this icosahedral deconstruction propagates and merges to form an amorphous region with 2--3 nm in width, leading to the following cavitation and brittle failure. More interesting, the deformation mechanism transforms from amorphization to stacking fault (SF) formation by microalloying aluminum (Al) into ${\mathrm{B}}_{4}\mathrm{C}$. This SF formation originates from the enhanced icosahedral slip as the Al is incorporated into the C-B-C chain to form a C-Al-C chain. This paper illustrates a deformation mechanism of superhard icosahedral solids and provides a strategy for suppressing the amorphization and brittle failure of ${\mathrm{B}}_{4}\mathrm{C}$.