Influence of Tip Geometry on Nanoscratching

Using molecular dynamics simulation, we study the influence of the tip geometry on indentation and scratching. We focus on the specific case of an Fe (100) surface scratched in [0 (1) over bar(1) over bar] direction. Three indenter shapes-spherical, conical and Berkovich-are investigated; for the cone, the semi-apex angle b is varied systematically. For conical indenters, we find a clear dependence on the semi-apex angle b: The friction coefficient decreases strongly with b in agreement with a simple analytical theory, while the hardness increases. For wider cones, the dislocation network under the groove increases in complexity. The pile-up produced outside the groove changes from a frontal to a lateral rim. The results for the Berkovich pyramid line up excellently with the cones if the traditional concept of an 'equivalent cone angle' is used. For the spherical indenter, however, we find deviations; it is not well described by its 'equivalent cone angle.' The sphere shows a smaller hardness and a higher friction coefficient than an equivalent cone. This finding quantifies the difference between blunt and sharp indenters in scratching.