Nanoplastic deformation of nanoindentation: Crystallographic dependence of displacement bursts

The present paper summarizes the crystallographic dependence of the displacement bursts in nanoindentation using single crystalline aluminum and copper with three kinds of surface indices, namely (0 0 1), (1 1 0) and (1 1 1). It is found that the experimental linear relation between the critical indent load and the burst width of the indent depth at the first displacement burst has significant crystallographic dependence. From the critical indent loads, the critical resolved shear stresses of the dislocation nucleation were estimated to be 3.3 GPa for Al and 3.6 GPa for Cu, using Hertz contact mechanics, which are both close to the ideal values. We explain the nanoplastic mechanics by a comprehensive energy balance model to describe the linear relation between the indent load and the burst width, and by the collective dislocation nucleation model consisting of three-dimensional dislocation loops to evaluate the number of dislocations nucleating. The former model can derive the linear relation qualitatively and link the burst width to the collective dislocation slipping. The latter relates the theoretical critical load and burst width with the function of the punch radius and the distance between dislocations nucleating dD, in which setting dD as about 10b (b is the Burgers vector) can fairly represent the Al experimental data.