Atomistic origin of shear induced quasi-plastic deformation in boron carbide

YD Shen and KM Reddy and J Li and MW Chen and Q An, ACTA MATERIALIA, 249, 118828 (2023).

DOI: 10.1016/j.actamat.2023.118828

Superhard materials typically exhibit limited plastic deformation due to their strong covalent and ionic bonding. Identifying the deformation mechanisms is crucial to enhance their mechanical properties. By combining molecular dynamics simulations with transmission electron microscopy experiments, we determine the shearinduced crystal defects and their related deformation mechanisms, referred to quasi-plasticity, in superhard boron carbide (B4C). Surprisingly, we identify an anomalous quasi-plastic deformation in B4C with a larger failure strain under ideal shear deformation along the (111)112 slip system. This behavior arises from slip band formation and propagation, which is stabilized by the newly formed bonding between icosahedra clusters and atomic chains during deformation. The slip band and crystal matrix share a dislocation-like interface, which serves as the nucleation site for the amorphous band formation at a large shear strain. In contrast, the dislocationlike mechanism mediated amorphization is observed in B4C as it shears along (021)512, (111)211 and (512) 153 slip systems. We derive the activation volume and energy for the quasi-plastic deformation, which are much lower than those for other deformation mechanisms (e.g. shear banding in amorphous alloys). Therefore, the quasi-plastic deformation may play an essential role in the brittle failure of single crystal B4C.

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