Scratching of hcp metals: A molecular-dynamics study

Abstract

Using molecular-dynamics simulation, we study the scratching of Ti and Mg crystals by a hard tip. Both the basal and a prismatic surface orientations are considered. We focus on the characterization of defects and plasticity in the crystal. Among the various types of dislocations generated the partials b=13〈1¯100〉 are most prominent. During scratch dislocation reactions constantly reorganize the dislocation network adherent to the scratch groove. Plastic activity is more pronounced for the prismatic surface, where dislocation loops – mainly consisting of b=13〈2¯110〉 and 13〈1¯100〉 dislocations – are emitted into the substrate. Under the basal surface I2 intrinsic stacking faults, corresponding to b=13〈1¯100〉 partials are formed parallel to the scratch groove bottom, while they are oriented perpendicular to the surface under the prismatic surface. We find that mainly the {011¯0}〈2¯110〉 slip system is activated, and relate the form of the pile-up generated to this slip. The tangential hardness is systematically smaller than the normal hardness under scratching. The basal surface has smaller hardness than the prismatic surface.