Collective Mechanical Behavior of dislocation Network Developed under Indentation

利用透射电子显微镜（TEM）观察了单晶硅和铝的压痕诱导塑性区截面，了解了压痕作用下的内部结构变化。通过聚焦离子束（FIB）技术，从样品上切下一小块包括压痕区域的薄片，并将其减薄至几百纳米厚度。在硅的情况下，与经过再结晶热处理的样品相比，卸载后的静水压力诱导相变恢复到具有不同晶体取向的金刚石结构。由60度位错和螺旋位错组成的完美位错可以在相变与金刚石体的边界处产生。通过分子动力学模拟研究了位错的发射和运动机理。另一方面，在单晶铝中发现，在最大剪应力区组织了小于1微米的亚晶粒。这似乎是位错网络的一种自组织，是集体力学行为的结果。在纳米压痕试验中，在压痕载荷与压痕深度的关系中发现了不稳定位移爆裂现象，这很可能与位错发射有关。本研究采用分子动力学方法模拟了单晶铝中的位错发射和棱柱位错环的形成。重点讨论了两种不同类型压头对应力分布的影响以及三种不同嵌入原子类型势对原子间相互作用描述的影响。结果表明，位错是由压痕造成的严重损伤的表面原子层发出的，由表面发出的剪切环与交叉滑移机制之间的不稳定反应产生的棱柱形位错环具有相同的滑动方向，但不在滑动面上。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