高应变率拉伸下纳米空洞的成核与早期生长

利用分子动力学方法研究了单晶铜中纳米空洞的成核与早期生长过程.研究结果表明：高应变率拉伸作用下,在缺陷原子或空位密集区首先启动（111）-211],（111）-211],（111）-211],（111）-211]4个滑移系的位错.空洞在特定滑移系层错交叠,即（111）-211]和（111）-211]滑移系的层错交叠以及（111）-211]和（111）-211]滑移系的层错交叠形成的空穴串处成核.这些空穴串分别沿011]和011]方向,与加载方向垂直.相对于其他的滑移系交叠,这种滑移系交叠形成的空穴串的截面积最大.此后,空洞通过发射位错长大,形状类似长条形;伴随其他类型位错的生长,空洞逐渐演化为柱形-椭球形-类球形.对于含双空洞的单晶铜体系,受已存空洞周围应力分布的影响,多个滑移体系同时启动,空洞在3个滑移系的层错交汇点的空穴处成核,其形状受交汇处位错线运动方向的影响,类似扁三角形,并在位错的滑移和攀移作用下逐渐演化为类球形.我们根据畸变场计算了3个层错面交叠处的空穴体积,发现108个不同交叠构型中,只有4种构型的交叠引起的空穴体积最大,空洞成核容易,其他情况不能使空洞成核.

The nucleation and growth of nanovoids under high tensile strain rate

The nucleation and growth of voids under high tensile strain rate are investigated using molecular dynamics method. Our simulation results show that dislocations of （111） 211],（111） 211]（111） 211],（111） 211]slip system are first initiated in concentration regions of defects and vacancies. Voids nucleate in vacancy strings that are generated via the continuous jogging of the stacking fault of specific slip system. Vacancy strings are along 011] and 01 1] directions and vertical to the loading directions. These specific slip systems overlap results in largest cross-sectional area of vacancy strings. Since then, the nucleated voids grow up via dislocation emission, and their shapes gradually evolve into strip-like, cylindrical, ellipsoidal, and spherical. In single crystal copper with double void inclusions, more slip systems are simultaneously initiated under the stress distribution of the existing voids. In this case, the new generated voids nucleate at the specific positions where the stacking faults of the three slip systems intersect. Influenced by the moving directions of dislocation lines, their shapes are first flat-triangle-like, and then gradually evolve to spherical-like with slipping and climbing of dislocations. We also calculate the vacancy volume in the junctions when three stacking faults encounter according to distortional filed distribution, finding that among 108 different crossing configurations, only four configurations result in maximum vacancy volume that enable void to nucleate, void can not nucleate in other condition.