Yielding and jerky plasticity of tilt grain boundaries in high-temperature graphene

TL;DR

This study investigates the high-temperature mechanical behavior of graphene grain boundaries, revealing a transition from brittle fracture to plastic flow and jerky plasticity driven by dislocation dynamics intrinsic to 2D systems.

Contribution

It introduces a phase field crystal model to explore temperature-dependent deformation mechanisms and identifies a plastic transition and jerky plasticity in graphene at ultrahigh temperatures.

Findings

Brittle fracture dominates at high temperature (~3350 K).

Dislocation motion causes jerky plasticity in graphene.

Plastic transition occurs with increasing temperature.

Abstract

Graphene is well known for its extraordinary mechanical properties combining brittleness and ductility. While most mechanical studies of graphene focused on the strength and brittle fracture behavior, its ductility, plastic deformation, and the possible brittle-to-ductile transition, which are important for high-temperature mechanical performance and applications, still remain much less understood. Here the mechanical response and deformation dynamics of graphene grain boundaries are investigated through a phase field crystal modeling, showing the pivotal effects of temperature and local dislocation structure. Our results indicate that even at relatively high temperature (around 3350 K), the system is still governed by a brittle fracture and cracking dynamics as found in previous low-temperature experimental and atomistic studies. We also identify another type of failure dynamics with low-angle grain boundary disintegration. When temperature increases a transition to plastic deformation is predicted. The appearance of plastic flow at ultrahigh temperature, particularly the phenomenon of jerky plasticity, is attributed to the stick and climb-glide motion of dislocations around the grain boundary. The corresponding mechanism is intrinsic to two-dimensional systems, and governed by the competition between the driving force of accumulated local stress and the defect pinning effect, without the traditional pathways of dislocation generation needed in three-dimensional materials.