Although the time-dependent deformation behaviors of microscale materials have been investigated through experiments with uniaxial loading conditions, the influence of the strain gradient has not been clearly clarified due to the lack of appropriate testing methods. In the current study, to investigate the stress relaxation behavior of microscale single-crystal copper (Cu) at room temperature, a quantitative in situ SEM bending experiment is presented using microcantilever specimens of single-crystal Cu. The microcantilever specimens were fabricated using a focused ion beam, and a tungsten (W) layer was deposited onto the front surface to eliminate the error induced by the penetration of the stiff indenter into the metallic specimen. The yield stress of microscale single-crystal Cu is determined to be 445 MPa by a monotonic loading test, showing an apparent size effect, and no strain hardening is observed due to single-slip deformation. On the other hand, the stress relaxation behavior of the microscale single-crystal Cu consists of both a continuous stress relaxation and an abrupt stress decrease due to a strain burst. The activated volume in each dwell stage is obtained by thermodynamics theory and is found to be mainly related to the abrupt stress decrease. The value of the activated volume indicates that the continuous stress drops in the 1st and 2nd dwell stages are attributed to the evolution of dislocation structures by the single slip on system B4, while the dislocation pile-up near the neutral plane leads to the dominance of cross slip on the stress relaxation behavior in the bending plateau. The proposed microcantilever bending experiment is applicable to explore the time-dependent deformation behavior of small-scale materials.

中文翻译：

---

室温下微尺度材料应力松弛的定量原位 SEM 弯曲方法

尽管已经通过单轴加载条件的实验研究了微尺度材料的时间相关变形行为，但由于缺乏适当的测试方法，应变梯度的影响尚未得到明确阐明。在目前的研究中，为了研究室温下微尺度单晶铜 (Cu) 的应力松弛行为，使用单晶 Cu 的微悬臂梁样品进行了定量原位 SEM 弯曲实验。使用聚焦离子束制造微悬臂梁样品，并在前表面沉积钨 (W) 层，以消除硬压头穿透金属样品引起的误差。通过单调加载试验确定微尺度单晶Cu的屈服应力为445 MPa，显示出明显的尺寸效应，并且没有观察到由于单滑动变形引起的应变硬化。另一方面，微米级单晶铜的应力松弛行为包括连续应力松弛和由于应变爆发引起的突然应力下降。每个驻留阶段的活化体积由热力学理论得出，发现主要与应力突然降低有关。激活体积的值表明，第一和第二驻留阶段的连续应力下降归因于系统 B4 上单次滑移的位错结构演化，而中性面附近的位错堆积导致弯曲平台中应力松弛行为的交叉滑移。