Atomic perspective of contact protection in graphene-coated high-entropy films

Covering graphene (Gr) coatings on high-entropy alloy (HEA) films is a promising approach to avoid its contact damage. However, current understanding regarding the underlying strengthening mechanisms of these systems at atomic level remains limited. Here, the contact mechanical behavior and strengthening mechanism of Gr-coated HEA films during nanoindentation were unravelled by means of molecular dynamics (MD) simulations. The results demonstrated that an increase of about 80.3% in indentation hardness of the composites can be endowed by covering a Gr layer, meaning a dramatically enhanced carrying capacity. More importantly, it would be further improved as Gr layers varied from monolayer to trilayer (increases of about 129.3% and 160.2% for the bilayer and trilayer cases, respectively). Moreover, we confirmed that due to the high in-plane stiffness, Gr coatings can effectively decrease the contact stress and inhibit the dislocation nucleation, which facilitated the decreased subsurface damage. Meanwhile, high-density Shockley and Stair-rod dislocations induced by an increase of the actual loading area synergistically promoted a strong strain hardening effect in the composites. It was deemed that the capability of contact protection of HEA films can be further improved after covering Gr coatings which can be ascribed to the high in-plane stiffness of Gr layers coupled with its induced strong strain hardening effect. These findings may contribute to the development and design of Gr-coated HEA composites with better mechanical properties.