Characteristic mechanism of fatigue crack propagation in submicron-thick freestanding copper films
Characteristic mechanism of fatigue crack propagation in submicron-thick freestanding copper films
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亚微米厚独立铜膜疲劳裂纹扩展特征机制
DOI：
10.1016/j.mspro.2014.06.090
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
K. Minoshima
中科院分区：
文献类型：
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作者：
T. Kondo;H. Hirakata;M. Sakihara;K. Minoshima
在三个应力比，R= 0.1，0.5和0.8的约500 nm厚的独立的铜（Cu）膜的疲劳裂纹扩展的力学和机制进行了评估。疲劳裂纹扩展速率（da/dN）与最大应力强度因子（Kmax）在高Kmax区（Kmax≥ 4.5MPam ~（1/2））具有一致的特征，表明Kmax是疲劳裂纹扩展的主导因素。在此区域，疲劳裂纹扩展伴随着厚度方向的颈缩变形，与R无关。相比之下，在低Kmax区域（Kmax< 4.5 MPam 1/2），da/dN随着R的降低而增加。在此区域内，断裂机制取决于R。在较高的R值（R= 0.8），疲劳裂纹扩展的拉伸断裂模式类似于在高Kmax区。另一方面，在较低的R值（R= 0.1和0.5）下观察到特征性机制。沿沿着3孪晶界在疲劳裂纹的前面形成了向面外方向突出的薄带，疲劳裂纹优先通过这些薄带扩展。在疲劳裂纹尖端附近形成的薄带的横截面观察显示，在膜表面处的侵入和挤出是明显的，证实了Cu膜中的疲劳裂纹扩展是由低Kmax区域中的侵入/挤出引起的。这一机理与本体对应物的机理有很大不同。此外，通过在低Kmax或低Δ K区域的疲劳裂纹的原位FESEM观察，观察到裂纹闭合。
The mechanics and mechanisms of fatigue crack propagation in approximately 500 nm thick freestanding copper (Cu) films were evaluated at three stress ratios,R= 0.1, 0.5 and 0.8. The fatigue crack propagation rate (da/dN) versus the maximum stress intensity factor (Kmax) exhibited coincident features in the high-Kmaxregion (Kmax≥ 4.5 MPam1/2) irrespective of stress ratioR, indicating thatKmaxwas the dominant factor in fatigue crack propagation. In this region, fatigue crack propagation wasaccompanied by necking deformation in the thickness direction, irrespective ofR. In contrast, in the low-Kmaxregion (Kmax< 4.5 MPam1/2), da/dNincreased with decreasingR. In this region, the fracture mechanism depended onR. At the higherRvalue (R= 0.8), the fatigue crack propagated in the tensile fracture mode similar to that in the high-Kmaxregion. On the other hand, acharacteristic mechanism was observed at the lowerRvalues (R= 0.1 and 0.5). Thin strips projecting in the out-of-plane directions formed ahead of the fatigue crack along Σ3 twin boundaries, and the fatigue crack propagated preferentially through these thin strips. A cross-sectional observation of a thin strip forming in the vicinity of the fatigue crack tip revealed that intrusions and extrusions were apparent at the film surface, confirming that the fatigue crack propagation in the Cu films was induced by the intrusions/extrusions in the low-Kmaxregion. This mechanism is greatly different from that of bulk counterpart. Moreover, crack closure was observed byin situFESEM observation of a fatigue crack in the low-Kmaxor low-ΔKregion.