Mechanics of Fatigue Crack Propagation in Submicron-Thick Freestanding Copper Films

Abstract:

The dominant mechanics and mechanisms of fatigue crack propagation in approximately 500-nm-thick freestanding copper films were evaluated at three stress ratios, R = 0.1, 0.5, and 0.8. The fatigue crack propagation rate (da/dN) versus stress intensity factor range (ΔK) relation was dependent on the stress ratio (R): da/dN increased with increasing R. Plots of da/dN versus the maximum stress intensity factor (K_max) exhibited coincident features in the high-K_max region (K_max 4.5 MPam^1/2) irrespective of R, indicating that K_max was the dominant factor in fatigue crack propagation. In this region, the fatigue crack propagated in tensile fracture mode, or chisel-point fracture, irrespective of the R value. In contrast, in the low-K_max region (K_max < 4.5 MPam^1/2), da/dN increased with decreasing R. In this region, the fracture mechanism depended on R. At the higher R value (R = 0.8), the fatigue crack propagated in the tensile fracture mode similar to that in the high-K_max region. On the other hand, at the lower R values (R = 0.1 and 0.5), a characteristic mechanism of fatigue crack propagation appeared: within several grains, intrusions/extrusions formed ahead of the crack tip along the Σ3 twin boundaries, and the fatigue crack propagated preferentially through the intrusions/extrusions.

• Periodical: Advanced Materials Research (Volumes 891-892)
• Pages: 1681-1687
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.891-892.1681
• Online since: March 2014
• Authors: Hiroyuki Hirakata, Toshiyuki Kondo, Masayuki Sakihara, Kohji Minoshima
• Keywords: Copper, Crack Propagation, Fatigue, Stress Ratio, Thin Film

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