Analysis on Crack Driving Force at Stress Corrosion Cracking Tip Induced by Scratch in Nickel-based Alloy

Abstract:

Nickel-based alloys are commonly used to fabricate transfer tubes of pressurized water vapor generators. However, the stress corrosion cracking (SCC) induced by surface pits and scratches of the tubes is more sudden and has great influence on the safety and reliability of nuclear power plant. To understand the effects of the oxide morphology on the crack tip of scratched surface on SCC behavior of nickel-based alloy, the local stress-strain field at scratched crack tip in the presence of film-induced stress is simulated. Results show that wedge force is the major crack driving force that causes the SCC growth. Greater oxide thickness of scratch crack will give rise to wedge force and lead to an increase in SCC crack growth rate (CGR). The formation of oxide at crack tip will induce compressive stress, compressive strain and negative strain gradient, and thus retard the SCC propagation in the upper and lower part of the semi-ellipticalScrack front.