The effect of residual stress on the Preferential Intergranular Oxidation of Alloy 600

• Alloy 600 is susceptible to preferential intergranular oxidation in H2-steam at 480 °C.
• Residual tensile stresses enhance intergranular oxidation.
• Correlation between residual stresses and intergranular oxidation susceptibility.
• Novel micro-mechanical technique succeeded to measure stresses at microscopic level.

Alloy 600 was exposed to H2-steam to simulate the oxidation that occurs in high temperature water where this alloy is known to be susceptible to SCC. Analytical electron microscopy was employed to characterize the early stages of oxidation to aid in developing an understanding of the stress corrosion cracking behaviour of this alloy. The oxide consisted of sub-surface Cr2O3 particles, preferential intergranular oxidation and formation of surface Ni nodules. The measurements of residual stresses at the microscopic level using a recently-developed FIB micro-hole drilling technique revealed a correlation between local stress variations at the grain boundaries and the oxide morphology.