Fatigue Crack Initiation in Proton-Irradiated Austenitic Stainless Steel

Abstract

The effect of irradiation on slip band formation and growth and microcrack initiation behavior under low cycle fatigue in SUS316L austenitic stainless steel was investigated using accelerator-based proton irradiation and a low cycle fatigue test at room temperature in air. The mean space of the slip line in proton-irradiated specimens was 25-40% wider than that in unirradiated specimens under the same number of cycles, possibly due to localized deformation by proton irradiation. The microcrack initiation life of the proton-irradiated specimens was approximately 20% of that of the unirradiated specimens. While the microcrack initiation in the unirradiated specimens was observed at the grain boundary, twin boundary, slip band, and triple junction, that in the proton-irradiated specimens was observed only at the twin boundary and slip band, possibly due to irradiation hardening. The step-height of an extrusion near the microcrack was almost the same in the unirradiated and proton-irradiated specimens regardless of the initiation site (100-150 nm). Therefore, the microcrack initiation was considered to occur when the surface morphology change involving the extrusion exceeded the specific threshold value.

Mechanism of dislocation channel-induced irradiation assisted stress corrosion crack initiation in austenitic stainless steel

“…Dislocation channels are characterized by their width (~0.1 µm), spacing (generally 1-3 µm), and the amount of shear strain in the channel [11], [12]. The amount of shear strain in the dislocation channels is difficult to analyze experimentally.…”

Fundamental Mechanisms for Irradiation-Hardening and Embrittlement: A Review

“…A distinguished feature observed in irradiated materials is the formation of defect-free channels (or say dislocation channels) after plastic deformation [118] as illustrated in Figure 8. The dominant characters of defect-free channels involve the channel width (around 0.1 µm), inter-channel spacing (about 1-3 µm) and the amount of accumulated shear strain in channels [119,120]. Through measuring the step height on the surface of irradiated samples and the offset caused by the channel-grain boundary intersection, the amount of shear strain in channels is estimated to be about two orders of magnitude higher than that of bulk materials without irradiation effect [121].…”

Observations of fatigue crack behaviour in proton‐irradiated 304 stainless steel

“…Fenici and Suolang found that proton‐irradiated austenitic steel was more resistant to crack initiation and had a reduced crack growth rate compared with unirradiated controls when using load‐controlled testing. Nogami et al found the opposite behaviour in low‐cycle, strain‐controlled fatigue testing where proton irradiation reduced the time for crack initiation. Murase et al found an increase in fatigue life due to proton irradiation, as did Shulov and Nochovnaya for metals subject to heavy ion irradiation.…”