Atomistic insights into the role of graphene sheets in CoCrNi/graphene composites

Abstract

Dislocation nucleation and interactions at the metal/graphene (Gr) interface are crucial for understanding metal/Gr composites, especially in multi-principal element alloys (MPEAs), where unique compositional complexity adds further intricacies. This study uses atomic simulations to investigate interfacial characteristics and dislocation behaviors in CoCrNi/Gr composites. We identify six stacking configurations at the equilibrium interface and analyze misfit dislocation patterns, showing how lattice distortion and short-range order (SRO) influence interface structure. For dislocation nucleation, a high Schmid factor is necessary but not solely sufficient to determine the preferred slip system. Additional factors, such as misfit dislocation stress and orientation, affect nucleation sites within the interface defect network. Although lattice distortion and SRO do not shift nucleation sites, they create a heterogeneous nucleation mode by altering local chemical environments and shear stress. Further, the twist angle of graphene affects dislocation nucleation, underlining the generality of a nucleation criterion controlled by interface dislocation structure. Our study also clarifies how dislocations interact with finite and infinite graphene sheets. With finite-sized graphene in CoCrNi/Gr, blocked dislocations cross-slip along the weak interface, while remaining segments bypass and do not merge, compared with the dislocation reflection and Orowan-like mechanism in pure metal/Gr. With infinite-length graphene, interface obstruction and dislocation nucleation on the opposite side dominate. Lastly, we uncover how graphene's unique out-of-plane deformation capability enables twinning nucleation. These findings extend beyond CoCrNi/Gr composites, offering critical insights for predicting graphene's role in MPEA systems.