纳米Cu薄膜摩擦的桥域多尺度模拟分析

Multiscale simulation analysis of nano-Cu scratch process with bridging domain method

为了研究纳米材料的微观变形过程,采用桥域方法(Bridgingdomainmethod)对纳米尺度下Cu薄膜表面摩擦过程进行模拟,得到摩擦阻力和系统变形能随摩擦距离的变化曲线,摩擦过程中存在静-动摩擦转化点。微观分析表明:摩擦初期Cu薄膜变形处于弹性阶段,随压头前方原子堆积,Cu薄膜进入塑性变形阶段,直接出现4层及以上原子的稳定滑移,同时薄膜内发射出沿非摩擦方向的斜向滑移带。以中心对称系数为度量捕捉到斜向滑移带内V形位错结构的产生与演化过程,确定V形位错的运动对摩擦塑性阶段的变形释放起主导作用。此外,对位错原子数目的统计分析表明,宏观下薄膜表面摩擦阻力的多次突跳是由微观结构下不全位错向全位错的发展所致;最后定量化分析位错、孪晶等不同变形机制对总应变的贡献比重,得到摩擦过程中位错滑移原子的应变贡献比重稳定在10%左右,而孪晶迁移的应变贡献比重稳定在2.5%左右。

The scratch process of nano-Cu film has been investigated by using Bridging domain method.The friction force and system deformation energy vary with scratch distance in a similar trend,and there is a static-dynamic transition point in the scratch process.The microstructural analysis shows that the restorable strain occurs locally in Cu film at elastic stage,and then with the pile-up atoms in the front of indenter,the deformation of Cu film turns into plastic stage.The stable multilayer slip and a slanting slip zone along [1,0,1] are captured under the indenter.The generation and evolution of V shape dislocation in the slanting slip zone are analyzed via the centrosymmetry parameter,and the motion of V shape dislocation plays a leading role in the deformation release at plastic stage.In addition,statistical analysis for different dislocation atoms reveals that the development from partial dislocation to perfect dislocation leads to multiple jumps in friction force.The strain contribution analysis shows that the proportion of dislocation slip is finally about 10%,while twinning migration contributes less to the total strain,the proportion is finally about 2.5%.