Zener pinning by coherent particles: pinning efficiency and particle reorientation mechanisms

Zener pinning by coherent particles in copper-nickel model alloys has been studied using molecular dynamics simulations. It is found that 4 nm Ni particles were easily cut by migrating Cu grain boundaries during boundary passage, while 7-8 nm particles were harder to cut and coherency-to-incoherency change occurred for some boundaries. Due to low volume fraction and easy cutting, 4 nm particles had a limited pinning effect on grain boundary motion. The increase in volume fraction and the suppressed cutting for 7-8 nm particles caused the boundary motion to be significantly retarded. Different grain boundaries exhibited the distinct ability to move past the same size particle. Significantly, with the pinning effect of Ni particles, misorientation dependence of boundary migration velocity became obvious, which is consistent with the findings in practical materials. During or after passage, the Ni particles were found to change orientation to become coherent with grain growth via various atomistic mechanisms. The mechanisms were discussed with respect to particle size and boundary misorientation.