Quantitative description of plastic deformation in nanocrystalline Cu: Dislocation glide versus grain boundary sliding
Quantitative description of plastic deformation in nanocrystalline Cu: Dislocation glide versus grain boundary sliding
复制标题
DOI：
10.1103/physrevb.77.134108
复制
发表时间：
2008-04-01
影响因子：
3.7
通讯作者：
Caro, A.
中科院分区：
文献类型：
--
作者：
Vo, N. Q.;Averback, R. S.;Caro, A.
采用分子动力学模拟方法研究了晶粒尺寸在5-20 nm范围内的多晶Cu的单轴塑性变形。我们开发了一个定量分析的塑性使用本地化滑移矢量分离的贡献位错活动的晶界滑动。这两种机制之间的竞争取决于应变速率和晶粒尺寸，位错活动随晶粒尺寸的增加而增加，但随应变速率的增加而减少。对于晶粒尺寸为5 nm的样品，在1 × 10（8）s（-1）的速率下，稳态变形期间位错贡献约50%的总塑性应变，但在1 × 10（10）s（-1）的速率下，该比例降低至35%。当晶粒尺寸增加到20 nm时，位错占应变的90%，即使在1 × 10（10）s（-1）下也是如此。在塑性变形的初始阶段，由于晶界内的应变诱导松弛过程，晶界滑动最初随应变而减小。在应变至20%的过程中，晶粒也旋转几度;旋转速率（每单位应变）随应变速率略微降低。最后，我们计算了在塑性变形过程中的强制原子混合量。晶粒内部的原子对之间的均方分离距离随着应变以与它们分开的距离成比例的速率增加（即，混合是超扩散的），但是对于大于晶粒尺寸的对分离，该速率变得与分离距离无关。
Uniaxial plastic deformation of polycrystalline Cu with grain sizes in the range of 5-20 nm was studied by using molecular dynamics computer simulations. We developed a quantitative analysis of plasticity by using localized slip vectors to separate the contributions of dislocation activity from grain boundary sliding. We conclude that the competition between these two mechanisms depends on strain rate and grain size, with the dislocation activity increasing with grain size but decreasing with increasing strain rate. For samples with a 5 nm grain size, dislocations contribute approximate to 50% of the total plastic strain during steady state deformation at a rate of 1x10(8) s(-1), but this fraction decreases to 35% at a rate of 1x10(10) s(-1). When the grain size is increased to 20 nm, dislocations account for 90% of the strain, even at 1x10(10) s(-1). During the initial stages of plastic deformation, grain boundary sliding initially decreases with strain owing to strain-induced relaxation processes within the grain boundaries. The grains also rotate a few degrees during straining to 20%; the rate of rotation (per unit strain) slightly decreases with strain rate. Lastly, we computed the amount of forced atomic mixing during plastic deformation. The mean square separation distance between atom pairs within grain interiors increases with strain at a rate proportional to their distance apart (i.e., the mixing is superdiffusive), but for pair separations greater than the grain size, this rate becomes independent of the separation distance.