不同晶体取向下纳米压痕的多尺度模拟

Multi-scale simulation of the deformation in nano-indentation under different crystal orientations

采用准连续介质多尺度方法模拟面心立方金属铝单晶薄膜的纳米压痕变形过程.对薄膜分别采用三种不同的晶体取向(分别为x[111],y[10],z[2];x[2],y[111],z[10];x[10],y[001],z[0]),得到载荷-位移响应曲线.加载过程中,对晶体内部变形比较剧烈的部分画出原子图,并从微观角度分析产生剧烈变形的原因.结果表明,薄膜变形的微观机理因其晶体取向的不同而不同.在x[111],y[10],z[2]取向下,压头下压方向和晶体密排面平行,薄膜内部的主要变形机理为晶面滑移产生位错成核.该情况下材料的硬度较大,材料z方向位移较大;在x[2],y[111],z[10]取向下,压头下压方向与晶体密排面垂直,薄膜内部的主要变形机理为孪生变形.该情况下材料硬度最大,z方向位移也最大;在x[10],y[001],z[0]取向下,压头下压方向与晶体密排面呈一定角度,薄膜内部的变形机理为晶体层先滑移产生一小段位错,之后随着加载的进行在薄膜内部出现孪晶.该情况下材料硬度最小,z方向位移也最小.

The nano-indentation process of an fcc Al film under three different crystal orientations （x[111],y[1^-10],z[1^-1^-2]; x[1^-1^-2] ,y[111],z[1^-10] and x[11^-0],y[001],z[1^-1^-0]） are studied using the quasi-continuum method. The load-displacement responses of the film under different crystal orientations are presented respectively. The local atomics in the regions where sharp deformation occurred are plotted to analyse their mechanisms on atomic scale. The results show that the micro-mechanisms of the deformation in the film are different for different crystal orientations. Under the orientation of x[111], y[1^-10], z[1^-1^-2], in which the indentation direction is parallel to the close-arranged plane, the deformation in the film is mainly dominated by the dislocation nucleation caused by the slip of the plane, and the hardness and the out-of-plane displacement of the crystal are large. Under the x[1^-1^-2],y[111],z[1^-10] orientation, in which the indentation direction is perpendicular to the close-arranged plane, the deformation in the film is mainly dominated by the deformation twinning, and both the hardness and the out-of-plane displacement of the crystal are the largest. Under the x[11^-0], y[001], z[1^-1^-0] orientation, in which the indentation direction is at some degrees inclined to the close-arranged plane, the deformation in the film starts from a small dislocation line nucleating on a slip plane at the beginning of the loading and then deformation twinning is formed with the increasing loading, and the hardness and the out-of-plane displacement of the crystal are the smallest.