Collective Mechanical Behavior of dislocation Network Developed under Indentation

用透射电子显微镜观察了压痕诱导塑性区为单晶硅和铝的横截面，以了解它们在压痕作用下的内部结构变化。利用聚焦离子束(FIB)技术，从样品中切下一小块包含凹陷区的小块，并将其减薄至几百纳米厚。在硅的情况下，静水压力诱导的相变恢复到卸载后与块体不同晶体取向的金刚石结构，并与经过再结晶热处理的样品进行了比较。由60°位错和螺旋位错组成的完美位错可以从相变和金刚石块体的边界发射出来。并用分子动力学模拟研究了位错的发射和运动机制。另一方面，它可以在…的案例中找到在最大剪应力区，更多的单晶铝是由小于1微米的亚晶组织的。这似乎是位错网络的自组织，这是集体力学行为的结果之一。在纳米压痕测试的压痕载荷与压痕深度之间的关系中观察到的不稳定位移爆发的新发现很可能与位错发射有关。本文用分子动力学方法模拟了单晶铝中的位错发射和棱柱状位错环的形成。重点讨论了两种不同类型的压头对应力分布的影响，以及三种不同嵌入原子类势对原子间相互作用的影响。结果是，由于压头的作用，位错从严重损伤的表面原子层中发射出来，表面发射的剪切环与交叉滑移机制之间发生不稳定的反应，得到了滑移方向相同但不在滑移面上的棱柱型位错环。较少

Cross sections of the indent-induced plastic zones is single crystalline silicon and aluminum are observed by the transmission electron microscopy (TEM) in order to know their internal structural changes under indentation. A tiny piece involving the indented region is cut from the sample and thinned until a few hundred nanometer thickness by means of the Focus Ion Beam (FIB) technique. At the case of silicon, the hydrostatic pressure-induced phase transition recovers to the diamond structure with the different crystallographic orientation from the bulk after unloading, being compared with the sample having received the heat treatment for recrystallization. Perfect dislocations consisting of the 60 degree dislocations and screw dislocations may be emitted from the boundary between the phase transition and the diamond bulk. Emission and movemeat mechanism of the dislocation are also investigated with help of the molecular dynamics simulations. On the other hand, it is found at the case o … More f single crystalline aluminum that the subgrains less than one micron are organized at the maximum shear stress region. It seems to be one of the self-organization of dislocation network as a result of the collective mechanical behaviors.New finding of unstable displacement burst observed in the relation between the indent load and indent depth of a nanoindentation test is much possible to be related to dislocation emission. In the present research, the dislocation emission and the prismatic dislocation loop formation in a single crystalline aluminum are simulated by the molecular dynamics. Effects of the stress distribution due to two different types of indenters and of the interatomic description by three different embedded atom type potentials are discussed with much emphasis. At a result, the dislocations are emitted from the severely damaged surface atomic layer due to the indenter and the prismatic dislocation loops, which have the same gliding direction but not on the glide plane, are attained by unstable reaction between the shear loops emitted from the surface and cross slip mechanism. Less