Grain boundary finite length faceting

Abstract

We study symmetrical and asymmetrical aluminium grain boundary faceting with molecular dynamics simulations employing two embedded atom method potentials. Facet formation, coarsening, and the reversible phase transition of ∑ 3 { 1 1 0 } boundary into ∑ 3 { 1 1 2 } twin, and vice versa, are demonstrated in the simulations and the results are consistent with earlier experimental studies and theoretical models. The ∑ 11 { 0 0 2 } 1 / { 6 6 7 } 2 boundary shows faceting into { 2 2 5 } 1 / { 4 4 1 } 2 and { 6 6 7 } 1 / { 0 0 1 } 2 boundaries and coarsens with a slower rate when compared to ∑ 3 { 1 1 2 } facets. However, facets formed by { 1 1 1 } 1 / { 1 1 2 } 2 and { 0 0 1 } 1 / { 1 1 0 } 2 boundaries from a { 1 1 6 } 1 / { 6 6 2 } 2 boundary are stable against finite temperature annealing. In the above faceted boundary, elastic strain energy induced by atomic mismatch across the boundary creates barriers to facet coarsening. Grain boundary tension is too small to stabilize the finite length faceting in both ∑ 3 { 1 1 2 } twin and asymmetrical { 1 1 1 } 1 / { 1 1 2 } 2 and { 0 0 1 } 1 / { 1 1 0 } 2 facets. The observed finite facet sizes are dictated by facet coarsening kinetics which can be strongly retarded by deep local energy minima associated with atomic matching across the boundary.