Abstract
Nanoindentation simulations are performed for a Ni(111) bi-crystal, in which the grain boundary is coated by a graphene layer. We study both a weak and a strong interface, realized by a and a twist boundary, respectively, and compare our results for the composite also with those of an elemental Ni bi-crystal. We find hardening of the elemental Ni when a strong, i.e., low-energy, grain boundary is introduced, and softening for a weak grain boundary. For the strong grain boundary, the interface barrier strength felt by dislocations upon passing the interface is responsible for the hardening; for the weak grain boundary, confinement of the dislocations results in the weakening. For the Ni-graphene composite, we find in all cases a weakening influence that is caused by the graphene blocking the passage of dislocations and absorbing them. In addition, interface failure occurs when the indenter reaches the graphene, again weakening the composite structure.
Highlights
Graphene-metal nanocomposites are an interesting class of materials which exhibit improved mechanical properties [1]
By comparing nanoindentation of such bi-crystals (Section 3) with those where the the grain boundary is filled with a graphene flake (Section 4), we can identify the mechanisms of how graphene affects the dislocation propagation in such systems
(ii) A twist grain boundary is generated in this system by rotating the upper 3 nm of the Ni block by an angle θ around the [111] direction; see Figure 2
Summary
Graphene-metal nanocomposites are an interesting class of materials which exhibit improved mechanical properties [1]. Besides uniaxial compression or tension tests, simulated nanoindentation offers an adequate means to introduce dislocations into the system and to study their propagation and interaction, as has been shown in previous studies of multilayered [8,16], nanolaminated [17,18], and nanotwinned [19,20,21,22] materials. Ni constitutes a prominent metal-matrix material and has been used in a variety of both experimental and computational studies of Ni-graphene nanocomposites [23,24,25,26,27,28,29,30]. By comparing nanoindentation of such bi-crystals (Section 3) with those where the the grain boundary is filled with a graphene flake (Section 4), we can identify the mechanisms of how graphene affects the dislocation propagation in such systems
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