纯铜[01■]倾侧型非共格Σ_3晶界结构稳定性分子动力学模拟研究

Molecular dynamics simulation on the struatural stability of [01■] tilt incoherent Σ_3 gain boundaries in pure copper

有研究表明,非共格Σ3晶界的行为在中低层错能面心立方金属晶界特征分布演化中发挥着重要作用.为了掌握不同界面匹配的非共格Σ3晶界的特性,本文利用分子动力学(MD)模拟方法首先研究了纯铜的[01■]倾侧型非共格Σ3晶界在700—1100K温度范围内和常压下的结构稳定性.MD模拟采用原子间相互作用长程经验多体势,步长为5×1015s.模拟结果表明:所研究的五个非共格Σ3晶界,其结构稳定性存在很大差异,其一般规律是,与(111)/(■11)共格孪晶界之间的夹角(Φ角)越小,晶界匹配值越大,则非共格Σ3晶界越稳定;反之亦然.Φ角最小的(255)/(■11)非共格Σ3晶界较稳定,在退火过程中几乎不发生变化.随着Φ角的增大,非共格Σ3晶界不再稳定,这类晶界会通过Miller指数较高一侧晶体每三层原子面合并为一层原子面(或Miller指数较低一侧晶体每一层原子面分解为三层原子面)的机理转变为亚稳的"台阶"状晶界,台阶面部分地处于精确的能量极低的{111}/{111}共格孪晶界上;当提高温度退火时,这种"台阶"状晶界最终会全部转变成稳定平直的{111}/{111}共格孪晶界.

It has been reported that incoherent Σ3 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 Σ3 boundaries with varied （h1k1l1）/（h2k2l2） interface matching, the structural stability of [011] tilt incoherent Σ3 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^-15s （5fs）. Simulation results show that the structural stabilities of [011^＋] tilt incoherent Σ3 grain boundaries are different from one another. The general trend is that the larger the angle （Φ） by which the grain boundary plane deviates from the ideal （111）/（1^＋11） twin boundary plane, the smaller the grain boundary matching value and thus the more unstable the incoherent Σ3 boundary. With the smallest Φ angle, （255）/（2^＋11） is stable and almost no structural change is observed during annealing processes. With increasing Φ angle, the incoherent Σ3 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.