Vacuum effects on fatigue crack growth in submicrometre‐thick freestanding copper films

Abstract

To clarify vacuum effects on fatigue crack growth in freestanding metallic thin films, experiments were conducted on approximately 500‐nm‐thick copper films inside a field emission scanning electron microscope. Fatigue crack growth accompanied by intrusion/extrusion formation occurred in vacuum, and da/dN was smaller than in air in the middle‐ΔK region (ΔK ≈ 1.7‐3.1 MPam1/2). Conversely, in the low‐ΔK region (ΔK ≲ 1.7 MPam1/2), da/dN was larger in vacuum than in air. Further, fatigue crack growth in vacuum occurred below the fatigue threshold in air (ΔKth,air). A nonpropagating crack after reaching ΔKth,air continued to propagate in vacuum when the environment changed from air to vacuum. This indicates that fatigue crack growth resistance is smaller in vacuum than in air under the same effective driving force. The fatigue damage area near the crack paths in vacuum in the low‐ΔK region became wider, suggesting that the nucleation of fatigue damage was enhanced in vacuum.

サブミクロン銅薄膜の疲労き裂進展特性に及ぼす表面酸化層の影響

“…化試験片 (Kondo et al, 2013(Kondo et al, , 2019bにおいても観察された． nm と 20 nm の薄膜の da/dN は等しく，また，toxide ≈ 0, 2 nm の薄膜に比べて da/dN が低下し，K ≈ 1.3 ~ 1.4 MPam 1/2 において下限界に至った．すなわち，酸化層が薄い場合(toxide ≈ 0, 2 nm)と厚い場合(toxide ≈ 6, 20 nm)に分ける と，Kth (toxide ≈ 0, 2 nm) < Kth (toxide ≈ 6, 20 nm)であった．…”

“…Fig.7Effect of surface oxide layer thickness t oxide on fatigue crack propagation properties. Fatigue crack propagation properties oft oxide ≈ 2nm are taken from the previous research(Kondo et al, 2019b).…”