Molecular dynamics simulation on the struatural stability of [0 1 (1)over-bar] tilt incoherent Σ3 gain boundaries in pure copper

It has been reported that incoherent Sigma(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 Sigma(3) boundaries with varied (h(1)k(1)l(1))/(h(2)k(2)l(2)) interface matching, the structural stability of [0 1 (1) over bar] tilt incoherent Sigma(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 x 10(-15) s (5 fs). Simulation results show that the structural stabilities of [0 1 (1) over bar] tilt incoherent E-3 grain boundaries are different from one another. The general trend is that the larger the angle (phi) by which the grain boundary plane deviates from the ideal (1 11)/((1) over bar 1 1) twin boundary plane, the smaller the grain boundary matching value and thus the more unstable the incoherent Sigma(3) boundary. With the smallest phi angle, (2 5 5)1((2) over bar 1 1) is stable and almost no structural change is observed during annealing processes. With increasing phi angle, the incoherent Sigma(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}/{11}planes. As the annealing temperature increases, such step-like boundaries will change completely into straight and stable {111}/{111}coherent twin boundaries.