Probing the Damage Recovery Mechanism in Irradiated Stainless Steels Using In-Situ Microcantilever Bending Test

Keyou S Mao,Kayla H Yano,Philip D Edmondson,Cheng Sun,Haozheng J Qu,Hao Wang,Janelle P Wharry

doi:10.3389/fmats.2022.823192

Abstract

Single crystalline microcantilevers are fabricated from the base metal and heat-affected zone (HAZ) of a laser welded, neutron irradiated austenitic stainless steel, for scanning electron microscope (SEM) in-situ bending. In the HAZ, cantilevers exhibit higher yield point and lower crack tip blunting displacement than in the base metal and unirradiated archive specimen. These results suggest that radiation-induced defects harden the base metal, whereas the HAZ exhibits annealing of defects leading to mechanical softening. Dislocation nucleation ahead of the crack tip is responsible for ductile blunting behavior and provides a pathway to mitigating helium-induced cracking during weld repairs of irradiated materials.

Highlights

Life extensions of commercial light water nuclear reactors (LWRs) require damage-free crack repairs in both in-core and near-core structural components
The in-situ microcantilever bending videos further verify that no crack tip propagation or opening has occurred during the bending tests, which is consistent with the post-mortem images of the crack tip
No statistically significant variation in yield point is observed across all specimens, with average yield points being highest in the archive specimen at 473 ± 40 (Figure 3A), lowest in the irradiated base metal at 407 ± 31 (Figure 3B), and 445 ± 56 for the irradiated heat-affected zone (HAZ) (Figure 3C)

Summary

Introduction

Life extensions of commercial light water nuclear reactors (LWRs) require damage-free crack repairs in both in-core and near-core structural components. These weld repairs face challenges from the high helium (He) content, which can cause bubbles and cracks in structural materials following intense neutron irradiation (Morishima et al, 2004; Yamada et al, 2006). If conventional welding methods are used, the high temperature in the welding pool and the tensile stress developed upon cooling facilitate He bubble growth and exacerbates the intergranular He-induced cracking (HeIC) at the weld pool boundaries in the heat affected zone (HAZ) (Nishimura et al, 1998; Asano et al, 1999; Kanne et al, 1999). Microcantilever bending has been used to determine hydrogen embrittlement with respect to hydrogen-induced cracking (Deng et al, 2017; Deng and Barnoush, 2018); quantify the fracture toughness and dislocation structures of brittle materials through site-specific investigation

Methods

Results

Conclusion