The effect of graphene-metal interface on dislocation gliding and generation is a key element in understanding the mechanical properties of graphene metal-matrix composites. Graphene-metal interfaces can impede the propagation of dislocations, which enhances the mechanical properties, particularly the strength. On the other hand, the presence of such interfaces can also act as the dislocation source in the metal matrix, which can significantly weaken the material properties. This implies that graphene will not always improve the mechanical properties of metals, but alternatively, it can even significantly weaken the properties. Whether graphene acts as a dislocation sink or source primarily depends on the metal-graphene interface and also other pre-existing defects in the matrix. In this paper, we investigate these two opposing effects at the atomistic scale, using Molecular Dynamics (MD) simulations. To study the effect of the interface and to isolate the effects of dislocations from defects, we have reinforced a perfect crystal of nickel with graphene. We found that in the perfect crystal, the graphene in any interface structure acts as a defect and weakens the metal matrix. Each interface structure in the composite has a different effect on the system, and the topfcc structure of the graphene-nickel interface results in the least strength reduction. For graphene particles, apart from the interface, edges can also act as a dislocation nucleation site. We investigated the two edges –Zigzag and Armchair edge of graphene– and found that both the edges cause decrease in mechanical strength. Experimental results (always reported an increase in mechanical strength) are in contradiction to what we found in this work. The reason for this contradiction is that in the real metallic system, defects are already present, and those acts as a dislocation source more readily than the graphene. To verify this, we studied the metallic systems having defects in nickel crystal and the graphene is reinforced. Through these studies, we investigate the conditions in which the strengthening mechanisms overcome the weakening mechanisms, and improvement is observed in the mechanical properties, similar to some of the reported experimental works. Our results shed light on the deformation mechanisms in metal-graphene composites and can be used as a guide in designing and fabricating more efficient metal-matrix composites.
Charleston, J., Agrawal, A., & Mirzaeifar, R. (2020). Effect of interface configuration on the mechanical properties and dislocation mechanisms in metal graphene composites. Computational Materials Science, 178. https://doi.org/10.1016/j.commatsci.2020.109621