Strain hardening behavior in T-carbon: A molecular dynamics study

[Display omitted] •Strain hardening makes T-carbon strong and ductile in compressive deformation.•Strain hardening of T-carbon is remarkable in conventional carbon-based materials.•Strain hardening of T-carbon is highly dependent on its graphitization.•The plasticity mechanism drives new strategies for advanced carbon structures. T-carbon, a new carbon allotrope essentially composed of intra-tetrahedron bonds and inter-tetrahedron bonds, has attracted strong scientific interest in recent years due to its excellent mechanical performance for a wide range of applications. This study demonstrates that strain hardening can endow T-carbon with exceptional mechanical strength at a high compressive strain under plastic deformation, which is rarely observed in conventional carbon-based materials. Molecular dynamics simulations reveal that this behavior occurs in T-carbon nanowires and is caused by graphitization, where their original sp3-dominated carbon network transforms into a stronger sp2-network. Further analysis shows that graphitization occurs due to the breaking of intra-tetrahedron bonds, which is dominated by the deformation behavior of inter-tetrahedron bond angles. Particularly, when the deformation angle is small, only a small portion of the strain energy is stored in the tetrahedrons, while the remaining energy is released by breaking the intra-tetrahedron bonds of T-carbon nanowires, thus leading to graphitization. Moreover, such underlying mechanisms behind strain hardening and graphitization are found to occur in bulk T-carbon. This strain hardening potentially enables T-carbon to overcome the strength–ductility tradeoff issue of high strength leading to ductility loss.