The use of UHP Ni and Ni Base Single Crystals to Study the Stress Corrosion Cracking Mechanisms of Alloy 600 in PWR Environment

Abstract

Stress corrosion crack initiation and propagation mechanisms of nickel base alloy 600 in PWR environment are determined thanks to the use of UHP single crystals. The deleterious influence of cathodic polarization on alloy 600 PWR SCC resistance is assessed by slow strain rate tests in primary water at 360°C. Moreover, transgranular SCC propagation is precisely observed and described on UHP single crystals. The possible mechanisms for SCC initiation and propagation are then discussed for both single and polycrystals. The use of UHP alloy 600 single crystals allows to clearly separate crack initiation and crack propagation mechanisms. The corrosion enhanced plasticity model is then proposed to describe the crack propagation processes, through hydrogen-dislocation interactions. The effects of such interactions are then macroscopically reproduced on UHP Ni single crystals.