Effects of Ar Ion Irradiation on Mechanical Properties and Microstructure of SA508 Grade 3 Class 1 and Class 2 Reactor Pressure Vessel Steels

TL;DR

This study examines how Ar ion irradiation affects the mechanical properties and microstructure of reactor pressure vessel steels, finding that nano-indentation is needed to detect surface-level changes.

Contribution

The study introduces the use of nano-indentation and TEM to detect irradiation effects in shallow surface layers of reactor steels.

Findings

Macro-mechanical tests showed no significant changes in bulk mechanical properties after irradiation.

Nano-indentation revealed increased indentation hardness in irradiated samples.

TEM confirmed a higher density of irradiation-induced defects in the irradiated specimens.

Abstract

This study investigates the effects of Ar ion irradiation on the mechanical properties and microstructure of SA508 Grade 3 Class 1 and Class 2 reactor pressure vessel steels. Three different fluence levels of Ar ion irradiation were applied to simulate accelerated irradiation damage conditions. Charpy impact and tensile tests conducted before and after irradiation showed no significant changes in bulk mechanical properties. Stopping and Range of Ions in Matter (SRIM) and Transport of Ions in Matter (TRIM) simulations revealed that Ar ion irradiation produces a shallow penetration depth of approximately 2.5 µm, highlighting the limitations of conventional macro-mechanical testing for evaluating irradiation effects in such a thin surface layer. To overcome this limitation, nano-indentation tests were performed, revealing a clear increase in indentation hardness after irradiation. Transmission electron microscopy (TEM) analysis using STEM–BF imaging confirmed a higher density of irradiation-induced defects in the irradiated specimens. The findings demonstrate that while macro-mechanical properties remain largely unaffected, micro-scale testing methods such as nano-indentation are essential for assessing irradiation-induced hardening in shallowly damaged layers, providing insight into the behavior of SA508 reactor pressure vessel steels under accelerated irradiation conditions.

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