面心立方铜晶体中空洞生长与贯通的尺寸效应

Size Effect in Void Growth and Coalescence of Face-centered Cubic Copper Crystals

利用分子动力学方法模拟沿拉伸方向排布的两个空洞在单轴拉伸作用下的动力学行为.着重研究不同尺寸空洞对其拉伸贯通过程的影响.结果表明,不同尺度的空洞都是通过空洞表面发射位错环长大与贯通的.空洞在弹性阶段沿加载方向缓慢长大,在塑性阶段沿垂直方向生长后形成类八面体形状.随空洞尺寸的减小,临界屈服应力逐渐增大.当半径较大时,位错对称成核、迁移,空洞沿加载方向被拉长,演化过程相似;当半径较小时,位错不对称成核,空洞沿垂直方向被拉长.空洞生长分为弹性变形、独立长大、融合贯通和平稳生长四个阶段.独立生长阶段随尺寸的减小逐渐缩短甚至消失.

Dynamics of a pair of voids located along loading direction under uniaxial tension is investigated using molecular dynamics method.Size effects in void growth and coalescence are studied.It shows that different-sized voids grow and coalesce through dislocation nucleating on void surfaces.In early elastic stage,voids grow along loading direction,then along vertical direction and finally form octahedral-like structures in plastic stage.Critical yield stress increases with decreasing of void size.If radius is large,dislocations nucleate and migrate symmetrically.Voids elongate in loading direction,and evolution process is similar.If radius is small,dislocations nucleate asymmetrically and voids elongate along vertical direction.The process of void growth may be characterized by elastic deformation,independent growth,coalescence and steady growth.Independent growth stage diminishes gradually as void size becomes smaller.