Sequence of deformation and cracking behaviours of Gallium-Arsenide during nano-scratching

GaAs {001} single crystals were scratched with constant normal loads (from 5 to 100 mN) using a Berkovich indenter tip with the edge moving parallel to the [110] direction with a constant velocity of 600 mu m s(-1). The scratching process generates both plastic deformation and various crack types, such as median, lateral and radial cracks. For the first time, an understanding of the different steps of the plastic deformation and cracking behaviour has been achieved. First, a localised dislocation cloud is formed below the surface and at the rear half of the indenter where the principal shear stress is maximal. Second, median cracks are nucleated by pile-up of converging dislocations below the surface along the ((1) over bar 10) plane. These median cracks propagate further as the indenter continues to increase the stress. Simultaneously, surface radial cracks are generated directly by the indenter tip. Then, deformation proceeds by plastic flow in the (111) plane. Fourth, lateral cracks are generated, and then radial cracks form off of these due to high stress intensity factor located at the sharp edges of the lateral cracks. The last phase is when lateral or radial cracks intercept each other, large chips are taken off from the surface. Apart from the sequence for the plastic deformation and cracking events, it is also demonstrated that the scratching depth, the residual pile-up, the residual scratch depth and all cracks follow a power-law dependence. Finally, it is found that the elastic recovery is more or less 15% which is explained by the value of the theological factor X obtained. (C) 2012 Elsevier B.V. All rights reserved.