Strain-induced grain growth and rotation in nickel nanowires
Virtual tensile tests of nanocrystalline nickel wires of initial 5 nm grain size were simulated at strain rates varying from 3x10(7) s(-1) to 1x10(9) s(-1) at 300 K, reaching deformation levels up to 36%. The virtual tensile tests allowed the study of the strain rate sensitivity of these nanowires, yielding an activation volume of similar to 2b(3), where b is the Burger's vector, consistent with grain boundary mechanisms of plasticity. Most importantly, after 3% deformation the grain size increased significantly during the deformation, with larger grains growing at the expense of the smaller ones as the deformation levels increase. The volume of each grain was monitored as a function of time and stress level. The results clearly indicate that the observed grain growth is stress driven, with grain size versus stress behavior being only weakly dependent on the strain rate and simulation time. Grain growth is also accompanied by grain rotation. The observations are interpreted in terms of the coupling of the relative motion of the grains parallel to the boundary and the motion of the boundary in the direction perpendicular to itself. Our results are consistent with a model where the deformation is accommodated by grain boundary sliding which in turn is coupled with grain boundary migration and rotation, producing grain growth.