Fatigue crack propagation properties of submicron-thick freestanding copper films in vacuum environment
Fatigue crack propagation properties of submicron-thick freestanding copper films in vacuum environment
复制标题
真空环境下亚微米厚独立铜膜的疲劳裂纹扩展特性
DOI：
10.1016/j.prostr.2016.06.173
复制
发表时间：
2016
期刊：
影响因子：
--
通讯作者：
Kohji MINOSHIMA
中科院分区：
文献类型：
--
作者：
Toshiyuki KONDO;Akihiro SHIN;Hiroyuki HIRAKATA;Kohji MINOSHIMA
为了研究真空环境对疲劳裂纹扩展特性的影响，在空气和真空环境中对约500 nm厚的自支撑铜薄膜进行了疲劳裂纹扩展实验。首先，我们在场发射扫描电子显微镜(FESEM)的真空室中建立了一套独立的铜薄膜疲劳裂纹扩展实验装置。疲劳裂纹扩展试验是在FESEM室(˜10-4PA)的环境空气和真空环境中进行的，在恒定最大应力和应力比0.1的载荷控制条件下进行。在此情况下，疲劳裂纹扩展的FESEM观察证实，在疲劳裂纹尖端之前形成了先前的侵入/挤出，然后在较低的应力强度因子(ΔK)范围内，疲劳裂纹优先通过这些侵入/挤出扩展。在较高的ΔK下，疲劳裂纹以拉伸断裂方式扩展。这些疲劳裂纹扩展机制与空气中的类似。疲劳裂纹扩展速率(da/dN)与应力强度因子范围(ΔK)之间的关系在ΔK≳4-5 MPam 1/2范围内大致处于一个较窄的范围内。另一方面，在ΔK≲4-5 MPam 1/2范围内，真空下的da/dN逐渐小于空气中的da/dN。FESEM观察证实，ΔK≲4-5 MPam 1/2下的断口形貌与环境有关：断口表面主要是在空气中观察到的平坦的断口，而在真空环境中，断口表面主要是粗糙度较小的钝性断口。这表明在真空环境中发生了可逆的循环滑移变形和重新焊接，导致da/dNin真空度比空气小。
Fatigue crack propagation experiments were conducted in approximately 500 nm thick freestanding copper (Cu) films in both air and vacuum environments to clarify the effects of vacuum environment on fatigue crack propagation properties. First, we newly developed an experimental setup for fatigue crack propagation experiments of the freestanding Cu films inside a vacuum chamber of a field-emission scanning electron microscope (FESEM). Fatigue crack propagation experiments were conducted in ambient air and vacuum environment of the FESEM chamber (˜10-4Pa) under load-control conditions with constant maximum stress and at a stress ratioRof 0.1.In situFESEM observations of fatigue crack propagation confirmed that preceding intrusions/extrusions were formed ahead of the fatigue crack tip, and the fatigue crack then propagated preferentially through these intrusions/extrusions in the lower stress intensity factor range (ΔK). In the higher ΔK, the fatigue crack propagated in tensile fracture mode. These mechanisms of fatigue crack propagation were similar to those in air. The relationships between fatigue crack propagation rate (da/dN) and stress intensity factor range (ΔK) in both environments were roughly within a narrow band in the region of ΔK≳ 4—5 MPam1/2. On the other hand, da/dNin vacuum became smaller than that in air in the region of ΔK≲ 4—5 MPam1/2. FESEM observations confirmed that the fracture surfaces morphologies depended on the environments in ΔK≲ 4—5 MPam1/2: flat fracture surface were mainly observed in air, whereas, in vacuum environment, blunt fracture surface with fine roughness were mainly observed. This suggests that reversible cyclic slip deformation and rewelding occurred in vacuum environments, resulting in smaller da/dNin vacuum than air.