Plastic deformation behavior during unloading in compressive cyclic test of nanocrystalline copper
Plastic deformation behavior during unloading in compressive cyclic test of nanocrystalline copper
复制标题
DOI：
10.1016/j.msea.2015.11.031
复制
发表时间：
2016-01
期刊：
影响因子：
6.4
通讯作者：
Jiangjiang Hu;Jinyu Zhang;Zhonghao Jiang;Xiangdong Ding;Yusheng Zhang;Shuang Han;Jun Sun;J. Lian
中科院分区：
文献类型：
--
作者：
Jiangjiang Hu;Jinyu Zhang;Zhonghao Jiang;Xiangdong Ding;Yusheng Zhang;Shuang Han;Jun Sun;J. Lian
变形粗晶多晶金属总是弹性卸载，加载过程中永久位错网络发达，阻碍位错运动，只允许应力的弹性松弛。然而，这种弹性卸载行为在纳米晶金属中是意想不到的，因为位错网络不能有效地在纳米级颗粒内形成。在这项工作中，我们报告了纳米晶铜在室温压缩循环试验中，在卸载区出现显著塑性变形的实验发现。卸载过程中产生的塑性应变的大小强烈依赖于加载和卸载速率。这种塑性卸载行为是由加载过程中积累的位错的快速吸收引起的，通过进行增量卸载试验，并基于晶界对位错的统计吸收和从晶界台阶发射位错的模型，建立了位错密度与加载和卸载速率之间的关系，对此进行了定量的解释。同时，还从滑移位错-孪晶界的相互作用角度分析了循环变形过程中变形结构的演变。
Deformed coarse-grained polycrystalline metals always unload elastically where permanent dislocation network well-developed in the loading regime hinders the movement of dislocations and allows only the elastic relaxation of stress. Such elastic unloading behavior is, however, unexpected in nanocrystalline metals because the dislocation network cannot effectively form inside nanometer-scale grains. In this work, we report the experimental finding of significant plastic deformation that emerges in the unloading regime in the compressive cyclic test at room temperature of nanocrystalline Cu. The magnitude of plastic strain produced during unloading depends strongly on loading and unloading rates. This plastic unloading behavior arises from the rapid absorption of dislocations accumulated during loading, which was quantitatively interpreted by performing the incremental unloading test and developing a relationship between the dislocation density and the loading and unloading rates based on the models of the statistical absorption of dislocations by grain boundaries and the dislocation emission from grain boundary ledges. Concurrently, the evolution of deformation structures during the cyclic deformation was also analyzed in terms of the interactions of gliding dislocation–twin boundaries.