Abstract
We investigated the fluence dependence of irradiation-induced solute cluster, dislocation loop, and very
small defect to reveal the hardening mechanism in surveillance test specimens from a reactor pressure
vessel steel with low-Cu content (0.04 wt%) using atom probe tomography (APT), weak-beam scanning
transmission electron microscopy (WB-STEM), and positron annihilation spectroscopy. A high number
density (>1023m3) of solute clusters mainly composed of Ni, Mn, and Si atoms were found in highly
neutron irradiated specimens (~1024 neutrons m2 (E > 1 MeV)) by APT. These solute clusters were one of
the main sources of hardening as reported previously. On the other hand, it was also revealed that
dislocation loops were formed with a number density of ~1022m3 in the high-fluence specimens by
WB-STEM. The estimated hardening due to dislocation loops was more than half of the actual hardening,
showing that dislocation loops are also main source of irradiation hardening at high neutron fluence with
the solid experimental evidences. Regarding specimens subjected to a low neutron fluence (~1023
neutrons m2), very small defects, not detected by either WB-STEM or APT, were formed by positron
annihilation spectroscopy. This result suggested that, at a low neutron fluence, the defects were the
initial hardening source and they may grow the dislocation loops observed by WB-STEM at high fluence
range
Details
Original language | English |
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Pages (from-to) | 402-409 |
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Number of pages | 8 |
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Journal | Acta Materialia |
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Volume | 155 |
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DOIs | |
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Publication status | Published - 14 Jun 2018 |
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