Collective Mechanical Behavior of dislocation Network Developed under Indentation

利用透射电子显微镜（TEM）观察了单晶硅和铝压痕诱导塑性区的横截面，以了解其在压痕作用下的内部结构变化。从样品上切下一个包含凹痕区域的小块，并通过聚焦离子束（FIB）技术将其减薄到几百纳米厚。在硅的情况下，流体静压引起的相变恢复到金刚石结构与卸载后的块体不同的晶体取向，与样品已接受再结晶热处理相比。在相变区与金刚石块体之间的界面处可能发射出由60度位错和螺型位错组成的完全位错。利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，它被发现在案件o ...更多信息 在最大剪切应力区，小于1微米的亚晶粒组织在单晶铝中。这似乎是位错网络自组织的一种集体力学行为的结果，在纳米压痕试验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。本文采用分子动力学方法模拟了单晶铝中位错发射和棱柱形位错环的形成。着重讨论了两种不同类型压头对应力分布的影响和三种不同嵌入原子势对原子间描述的影响。结果，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，而滑移方向相同但不在滑移面上的棱柱形位错环是由表面发射的剪切环与交叉滑移机制之间的不稳定反应而获得的。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