Multimillion-atom nanoindentation simulation of crystalline silicon carbide: Orientation dependence and anisotropic pileup

We have performed multimillion-atom molecular dynamics simulations of nanoindentation on cubic silicon carbide (3C-SiC) surfaces corresponding to three different crystallographic directions, (110), (001), and (111), using pyramidal-shaped Vickers indenter with 90 degrees edge angle. Load-displacement (P-h) curves show major and minor pop-in events during loading. Detailed analysis of the (110) indentation shows that the first minor discontinuity in the P-h curve is related to the nucleation of dislocations, whereas the subsequent major load drops are related to the dissipation of accumulated energy by expansion of dislocation loops and changes of slip planes. Motion of dislocation lines in the indented films involves a kink mechanism as well as mutually repelling glide-set Shockley partial dislocations with associated extension of stacking faults during the expansion of dislocation loops. Our simulations provide a quantitative insight into the stress distribution on slip planes and stress concentration at kinks and dislocation cores. The estimated Peierls stress is 7.5 GPa approximate to 3.9x10(-2)G, where G is the shear modulus. We find that similar deformation mechanisms operate during nanoindentation of the three surfaces but the calculated hardness values are different, the highest being 27.5 GPa for the (111) plane. Anisotropic pileup patterns are observed after the indenter is unloaded and they all reside on (111) and ((1) over bar(1) over bar1) slip planes. These patterns are closely related to dislocation activities on the two slip planes. The anisotropy is a consequence of the asymmetry of the 3C-SiC crystal in which only (111) and ((1) over bar(1) over bar1) slip planes are active out of the {111} family. (C) 2007 American Institute of Physics.