The stress corrosion cracking (SCC) susceptibility of Zr (UNS R60702), Zircaloy-4 (UNS R60804), and Ti (UNS R50400) in a 10-g/L iodine-methanol solution was studied. SCC, always preceded by intergranular corrosion (IGC), was observed in all the systems studied. The rate-controlling step of the IGC was found to be the diffusion of iodine to the tip of the crack. After the IGC reached a certain depth, a transition to a transgranular cracking mode took place. The length of IGC as a function of time was measured through interrupted strain rate tests. From these data and the overall (intergranular + transgranular) crack propagation rate, the rate for transgranular cracking was estimated. It was concluded that the transgranular part of the cracking was the real SCC process. The surface mobility-SCC mechanism was applied to explain the results obtained. According to this mechanism, the species responsible for inducing SCC are believed to be titanium tetraiodide (TiI4) and zirconium tetraiodide (ZrI4) for Ti and Zr alloys, respectively.

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NACE International
2005
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