Machine Learning Force Field for B-C Systems and Applications to Mechanical Deformation

The abnormal brittle failure of superhard boron carbide (B₄C) 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. The present study illustrates the shear induced amorphization process of B₄C from the molecular dynamics (MD) simulations using quantum mechanics derived machine-learning force field. The amorphization in B₄C 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 faults (SF) formation by microalloying aluminum (Al) into B₄C. This SF formation originates from the enhanced icosahedral slip as the Al is incorporated into the C-B-C chain to form C-Al-C chain. The present study illustrates a new deformation mechanism of superhard icosahedral solids and provides a new strategy for suppressing the amorphization and brittle failure of B₄C.