Influence of nanoscale Cu precipitates in a-Fe on dislocation core structure and strengthening

Atomistic simulations of the interaction of a screw dislocation in a-Fe with different size bcc Cu precipitates suggest two plausible strengthening mechanisms. For precipitate diameters in the range 1.5 nm<=d<=3.3 nm, the dislocation core structure within the Cu precipitate undergoes a polarized to nonpolarized transformation, leading to the dislocation pinning at the precipitate-matrix interface and the bowing out of the dislocation line. The calculated bow-out angle and resolved shear stress required to detach the dislocation from the precipitate are in agreement with recent experiments. The structural transition of larger (d>=3.3 nm) Cu precipitates under high shear stress is responsible for the loss of slip systems and hence for dislocation pinning.