Abstract
We used molecular dynamics simulations to study the scratching of Cu|Au nanolaminates of 5 nm layer thickness with a nanoscale indenter of 15 nm radius at normal forces between 0.5 μ N and 2 μ N. Our simulations show that Au layers wear quickly while Cu layers are more resistant to wear. Plowing was accompanied by the roughening of the Cu|Au heterointerface that lead to the folding of the nanolaminate structure at the edge of the wear track. Our explorative simulations hint at the complex deformation processes occurring in nanolaminates under tribological load.
Highlights
The “hardness” of a surface is determined through indentation experiments, which measure the force required for a macroscopic or microscopic indenter to penetrate a surface [1]
The burst of dislocations and plastic deformation is clearly captured by the atomic strain analysis shown in the inset of Figure 3
We have shown and discussed simulations of scratching Cu|Au metallic nanolaminates with an indenter of a size that corresponds to an atomic-force microscopy (AFM) tip for three different normal forces
Summary
The “hardness” of a surface is determined through indentation experiments, which measure the force required for a macroscopic or microscopic indenter to penetrate a surface [1]. A related technique, atomic-force microscopy (AFM), uses much smaller tips (on the order of ∼10 nm radius) and can be used to characterize the frictional properties of surfaces [6,7] but it is rarely used to probe surfaces in the plastic regime [8,9,10]. Using the AFM to probe surfaces offers the possibility to map local variations in hardness [11,12] and study the intrinsic strength of materials since the deformed volume under an AFM indenter is small and often defect-free [13]. It has been noted that in metals the relationship between grain-size and indenter radius is important and that the friction force depends on hardness only for grain sizes smaller than the indenter [18] Plastic deformation is responsible for part of the material loss during abrasive, sliding wear [8,14,15,16] and the plowing motion of asperities on the counter body contributes to the friction between two materials [16,17].
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