It is reported in the literature that Alloy C-22 (N06022) was foundsusceptible to stress corrosion cracking (SCC) in presence of bicarbonate ions, at temperatures higher than 60°Cand anodic applied potentials in the order of +400 mV SCE , when using slow strain rate tests (SSRT). This potential range of cracking susceptibility was associated to the instability of a film that may form on the surface. In order to elucidate the role of the alloying elements on the SCC susceptibility of nickel (Ni) based alloys, the following four Alloy C-22 (N06022), Alloy 600 (N06600), Alloy 800H (N08800) and Alloy Ni-201 (N02201)were tested under the same conditions. Results showed that even though C-22, 600 and 800 may have similar electrochemical anodic behavior, only C-22 may present a clear case of SCC at anodic potentials.
IntroductionAlloy C-22 (Ni-22%Cr-13%Mo-3%W-3%Fe) has been designed to resist corrosion in industrial environments for both oxidizing and reducing applications [1][2][3][4]. Thanks to these excellent properties it is one of the candidates for the corrosion resistant barrier of high level nuclear waste containers.Disposal in stable geological formations is the strongest worldwide alternative for the management of high level nuclear waste [5][6][7][8][9].Geological repositories are based on the multi-barrier principle (defense in depth), which consists in bringing a number of barriers, natural and engineering between the waste and the biosphere.The engineered barriers are specifically designed to prolong the isolation of waste and limit the potential for release of radionuclides [5][6][7][8][9]. The main engineering barrier is the container of the waste.Containers will serve in natural environments characterized by multi-ionic aqueous solutions [5][6][7][8][9][10][11]. It is estimated that the life of the corrosion resistant barrier of the container could be reduced due to stress corrosion cracking (SCC) [9, 12].The SCC susceptibility of AlloyC-22 has been studied in a variety of media and conditions [13][14][15][16][17][18][19][20][21][22][23].Alloy C-22 was found resistant to cracking in pure chloride environments. However AlloyC-22 was found susceptible to SCC in a potential range between 0.3 and 0.4 V SCE in simulated concentrated groundwater containing chloride, carbonate and bicarbonate above 65 °C [13][14][15][16][17][18][19][20][21][22][23].The studies also suggest that the coexistence of bicarbonate and chloride ions is particularly damaging to the resistance of Alloy C-22 to SCC. Pure bicarbonate solutions would cause SCC, but the susceptibility appears to increase with increasing chloride concentration in presence of bicarbonate [10][11][12][13][14][15][16][17][18].It was found experimentally that SCC will occur in a pH range between 8.5 and 10.5 [23]. It has been suggested that the susceptibility to SCC could be related to the occurrence of an anodic peak in the polarization curves in these media [16][17][18][19][20][21][22][23]. Dunn et al. showed that when Alloy C-22 suffers SCC in bicarbonate co...
