The role of intergranular chromium carbides on stress corrosion cracking of nickel base alloys in pwr primary water

F. Gaslain (1) , H.-T. Le (1) , C. Duhamel (1) , C. Guerre (2) , P. Laghoutaris (2)

1 CDM - Centre des Matériaux
2 CEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire)

Alloy 600 is used in pressurised water reactors (PWRs) but is susceptible to primary water stress corrosion cracking (PWSCC). Intergranular chromium carbides have been found beneficial to reduce PWSCC. Focused ion beam coupled with scanning electron microscopy (FIB/SEM) 3D tomography has been used to reconstruct the morphology of grain boundary oxide penetrations and their interaction with intergranular Cr carbides in Alloy 600 subjected to a PWR environment. In presence of intergranular Cr carbides, the intergranular oxide penetrations are less deep but larger than without carbide. However, the intergranular oxide volumes normalised by the GB length for both samples are similar, which suggest that intergranular oxidation growth rate is not affected by carbides. Analytical transmission electron microscopy (TEM) shows that the intergranular oxide consists mainly in a spinel-type oxide containing nickel and chromium, except in the vicinity of Cr carbides where Cr$_2$O$_3$ was evidenced. The formation of chromium oxide may explain the lower intergranular oxide depth observed in grain boundaries containing Cr carbides.

Keywords: Alloy 600; Chromium carbides; Stress Corrosion Cracking; TEM; Tomography

Domains: Nuclear Experiment [nucl-ex]; Nuclear Theory [nucl-th]

F. Gaslain, H.-T. Le, C. Duhamel, C. Guerre, P. Laghoutaris. The role of intergranular chromium carbides on stress corrosion cracking of nickel base alloys in pwr primary water. EMAS worshop 2015, May 2015, Portoroz, Slovenia. ⟨cea-02509151⟩