Role of Ag segregation on microscale strengthening and slip transmission in an asymmetric σ5 copper grain boundary

Micropillar compression was used to investigate whether Ag segregation to an asymmetric & sigma;5[001] grain boundary will lead to measurable strength differences compared to the pure copper bicrystal. Ag segregation was accomplished by deposition and subsequent annealing of an Ag thin-film applied on the surface of the Cu bicrystal. Atom probe tomography analysis indicated Ag segregation at the grain boundary with a peak concentration of 2.3 at.%. While the pristine & sigma;5 grain boundary shows a yield strength of 288 & PLUSMN; 18 MPa when compressing 1 & mu;m diameter pillars along 001, micropillars containing an Ag-segregated & sigma;5 grain boundary demonstrated an increased yield strength of 318 & PLUSMN; 17 MPa. In addition, post-deformation electron microscopy was carried out to examine the active slip systems and slip transmission across Ag-free and Ag-containing bicrystals. The results are compared to reference measurements of the adjacent single crystal grains. The 1 & mu;m pillar diameter promoted deformation governed by dislocation-grain boundary interactions for the bicrystalline pillars. This is the first time that changes in flow stress associated with grain boundary segregation have been quantified locally without interference from other mechanisms such as solid solution strengthening, formation of precipitates or changes in stacking fault energy. The results clearly indicate that purely geometrical models for slip transmission are not sufficient as the local atomic structure and composition influence dislocation transmission through grain boundaries.

Automated summary

Micropillar compression was used to study the effect of Ag segregation on the strength of a sigma 5 grain boundary in a copper bicrystal. Atom probe tomography analysis confirmed the presence of Ag segregation at the grain boundary. Micropillars containing Ag-segregated sigma 5 grain boundary showed higher yield strength than those without Ag segregation. Electron microscopy analysis revealed the difference in slip transmission mechanisms between Ag-free and Ag-containing bicrystals.