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Abstract: Crevice corrosion is considered possible if the corrosion potential (E corr) exceeds the repassivation potential for crevice corrosion (E rcrev). In this study, potentiodynamic polarization and potentiostatic hold were used to determine the E rcrev of similar and dissimilar metal crevices in the engineered barrier system of the potential Yucca Mountain repository in 0.5M NaCl, 4M NaCl, and 4M MgCl2 solutions at 95°C. The results were compared with data previously obtained using crevices formed between Alloy 22 and polytetrafluoroethylene. It was observed that, except for Type 316L stainless steel, all other metal-to-metal crevices were less susceptible to crevice corrosion than the corresponding metal-to-polytetrafluoroethylene crevices. Measurements of galvanic coupling were used to evaluate the crevice corrosion propagation behavior in 5M NaCl solution at 95°C. The crevice specimens were coupled to either an Alloy 22 or a Titanium Grade 7 plate using metal or polytetrafluoroethylene crevice washers. Crevice corrosion of Type 316L stainless steel propagated without repassivation. For all the tests using a polytetrafluoroethylene crevice washer, crevice corrosion of Alloy 22 was initiated at open circuit potential by the addition of CuCl2 as an oxidant, whereas no crevice corrosion of Alloy 22 was initiated for all the tests using Alloy 22 or Titanium Grade 7 metals as crevice washer. However, crevice corrosion propagation was found to be very limited under such test conditions. [Copyright &y& Elsevier]

The thermal stability of Alloy 22 affected by the precipitation of topologically close-packed (TCP) phases was investigated by means of experimental measurements and thermodynamic calculations. Both mill-annealed and welded specimens were exposed to various thermal aging and solution-annealing treatments. Microstructural analyses showed progressive precipitation of TCP phases in both the mill-annealed and welded specimens upon aging at 870 °C. Solution annealing of the welded material results in homogenization of the fusion zone; however, a high annealing temperature of 1300 °C leads to undesirable grain growth. All aging and solutionizing treatments of the welded material enhance precipitation of the secondary phases. Thermodynamic calculations predicted a solvus temperature of 1271 °C for the TCP phase in the interdendritic region as a result of Mo segregation during the solidification of the welded metal. This model prediction is consistent with experimental results showing that precipitates are observed in the welded material after various solution-annealing treatments. Results obtained from the present study suggest that solution-annealing treatments for Alloy 22 disposal containers should be carefully evaluated to assure that a homogeneous single-phase structure will be obtained. [ABSTRACT FROM AUTHOR]

A general model for predicting the localized corrosion repassivation potential of alloys in multicomponent electrolyte solutions is described. The model assumes that the status of localized corrosion is determined by competitive processes at the metal–salt film–solution interfaces leading to either metal salt or oxide formation. The model successfully predicts the observed effects of aggressive species, such as chloride and bromide, inhibiting species, such as nitrate, and non-aggressive species, such as acetate, for a number of Fe–Ni–Cr–Mo alloys. Furthermore, the model accurately predicts the effect of nitrate in a three-component system of chloride + nitrate + acetate, based only on parameters regressed for the constituent binary systems. [Copyright &y& Elsevier]