Molecular dynamics simulation on the struatural stability of [0 1 1] tilt incoherent 3 gain boundaries in pure copper

Abstract

It has been reported that incoherent 3 boundaries play an important role in the evolution of grain boundary characteristic distribution in the low to medium stacking fault energy in face-centered cubic metals. In order to ascertain the characteristics of incoherent 3 boundaries with varied (h1k1l1)/(h2k2l2) interface matching, the structural stability of [0 1 1] tilt incoherent 3 grain boundaries in pure copper, at temperatures ranging from 700 to 1100 K and under the normal pressure, was studied by molecular dynamics (MD) simulations. Long-range empirical potential (LREP) was used in the simulation in which the time-step was chosen to be 5 10-15 s (5 fs). Simulation results show that the structural stabilities of [0 1 1] tilt incoherent 3 grain boundaries are different from one another. The general trend is that the larger the angle () by which the grain boundary plane deviates from the ideal (1 1 1)/(1 1 1) twin boundary plane, the smaller the grain boundary matching value and thus the more unstable the incoherent 3 boundary. With the smallest angle, (2 5 5)/(2 1 1) is stable and almost no structural change is observed during annealing processes. With increasing angle, the incoherent 3 boundaries will not be stable any longer. They are usually changed into the meta-stable step-like boundaries during annealing by the mechanisms in which every three atomic layers in the high Miller-index side will merge into one atomic layer, or each atomic layer in the low Miller-index side decomposes into three atomic layers. Some of the steps of these boundaries are located at the exact {111}/{111} planes. As the annealing temperature increases, such step-like boundaries will change completely into straight and stable {111}/{111} coherent twin boundaries.