Twinning effects in the single/nanocrystalline cubic silicon carbide subjected to nanoindentation loading

Abstract Certain nanotwinned metals exhibit superior properties originating from the coherent internal interfaces; however, the deformation mechanisms responsible for strengthening/softening behavior in nanotwinned ceramics with covalent bonds are less clear. Here we carry out parametric atomistic simulations to provide insight into underlying deformations physics and responses of nanotwinned single/nanocrystalline cubic silicon carbide subjected to nanoindentation loading. Our simulations predict superior nanocontact resistance of nanotwinned single crystals, originating from the lattice dislocation blockage effects of coherent twin boundaries (CTBs), with a clear dependence on the CTB density. Nanotwinned nanocrystals exhibit an inverse Hall–Petch-like effect when the average grain size is larger than 8 nm, whereas fine grain size nanotwinned nanocrystals show slightly improved indentation hardness compared to their twin-free counterparts. We unravel that regardless of the CTB spacing, grain boundaries, lattice dislocation glide, and CTBs collectively accommodate the imposed plastic strain by the indenter in the nanocrystalline substrates with large grain sizes; however, with a decreasing grain size, the contributions by lattice dislocations and CTBs become limited. Our results also show that lattice dislocation-CTB interactions and transmission mechanisms, i.e. nucleation of twinning partial dislocations and formation and annihilation of point defects at CTBs, are insensitive to test conditions such as temperature, indentation speed, and indenter size. However, with decreasing CTB spacing, twinning dislocation occurs via dissociation and propagation of mostly Shockley partials rather than Frank partials trapped at CTBs. The structure-property findings in this study render unique insights to design novel nanotwinned silicon carbide nanostructures with improved indentation mechanical properties and high plasticity.