Scratching of hcp metals: A molecular-dynamics study

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 = 1/3 <(1) over bar 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 = 1/3 <(2) over bar 110 > and 1/3 <(1) over bar 100 > dislocations - are emitted into the substrate. Under the basal surface I-2 intrinsic stacking faults, corresponding to b = 1/3 <(1) over bar 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 {01 (1) over bar0} <(2) over bar 110 > 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. (C) 2015 Elsevier B.V. All rights reserved.