Nano-scale Plasticity in FCC and BCC Crystals as Determined by Compression Experiments and Dislocation Dynamics Simulations of Sub-micron Pillars.
作者单位：Department of Materials ScienceCalifornia Institute of TechnologyPasadenaCA 91125 USA Department of Mechanical EngineeringStanford University
会议名称：《US-China NSF Workshop and Summer Institute of Bio-and Nano-Mechanics and Applications》
会议日期：2007年
学科分类：07[理学] 070205[理学-凝聚态物理] 08[工学] 080501[工学-材料物理与化学] 0805[工学-材料科学与工程（可授工学、理学学位）] 0702[理学-物理学]
摘 要：正The strength of crystalline materials at reduced dimensions is important for the fabrication and reliable functioning of devices at nanometer scales such as micro- and nano-electro-mechanical systems（MEMS and NEMS）,bio-cell sensors,and fuel *** plastic flow stress of crystals,a size-independent property for the bulk,is found to strongly depend on sample size as it is reduced to micro- and nano-scales[1-4].Many models have been proposed to account for this size-dependence at small scales,including strain-gradient plasticity theories,applicable to inhomogeneous deformation of the material,*** nanoindentation[e.g.5-8].To investigate plasticity under homogeneous deformation,we have developed a micro-compression technique, where cylindrical sub-micron pillars fabricated by the focused ion beam（FIB） method are uniaxially compressed,and stress *** relationship is subsequently *** plastic flow stress increases dramatically as the diameter of the pillar decreases below one micron[1,2,9-11].This finding is interesting because it shows that the size effect can exist even without externally imposed strain gradients present in bending and indentation ***,several mechanisms have been proposed to explain the size effects associated with the micro-compression experiments[12,13].We expect that Dislocation Dynamics （DD） simulations,when quantitatively compared with the experiments,will reveal the underlying mechanisms of this size *** simulations were originally developed to model the plastic deformation of bulk crystals,but they have also been applied to thin films,in which we need to account for the effect of image stress on the dislocations due to the presence of free surfaces[14,15].In the course of this work,we have developed an efficient method to compute the image stress in an elastic cylinder using a set of analytical solutions[16].This allows for efficient DD simulations at the real length scale of the nanopillars.