The use of UHPNi and Ni base single crystals to study the stress corrosioncracking mechanisms of alloy 600 in PWR environment

Stress corrosion crack initiation and propagation mechanisms of nickel base alloy 600 in PWR environment are determined thanks to the use of UHP singl e crystals. The deleterious influence of cathodic polarization on alloy 600 PWR SCC resistance is assessed by blow strain rate tests in primary water at 360 degrees C. Moreover, transgranular SCC propagation is precisely obse rved and described on UHP single crystals. The possible mechanisms for SCC initiation and propagation are then discussed for both single and polycryst als. The use of UMP alloy 600 single crystals allows to clearly separate cr ack initiation and crack propagation mechanisms. The corrosion enhanced pla sticity model is dim 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.