Mitigating amorphization in superhard boron carbide by microalloying- induced stacking fault formation
Q An, PHYSICAL REVIEW MATERIALS, 5, 103602 (2021).
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. This paper illustrates the shear-induced amorphization process of B4C from 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 fault (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 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 B4C.
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