On the size effect in scratch and wear response of single crystalline copper

Abstract

Indentation hardness is a well-known material parameter for determining the resistance of a material to deformation. It is however known that indentation hardness alone cannot fully characterize anisotropic material strength in particular for single crystalline materials. Recently, it is shown that scratch hardness is a more suitable material property to characterize the wear response of crystalline materials. In this study, we use the mechanism-based strain gradient crystal plasticity to explore the size effect in the scratch behavior of single crystalline copper. Our simulations picture strong size effects in the scratch hardness value and pile-up magnitude. Interestingly, it shows that the degree and nature of size-dependency for these two parameters varies significantly and oppositely by the scratch direction. For instance, while [001] direction shows the highest degree of size effect in scratch hardness, it presents the lowest pile-up size effect. This opposite effect is explained in terms of the contribution of different slip systems to dislocation resistance and work hardening. We also show that scratch hardness, which takes into account both the size effect and crystallographic direction dependence, is an appropriate material property for wear characterization.