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The effects of Cr, Mo, and W on the crevice corrosion of a number of commercial Ni-Cr-Mo(W) alloys in 1.0 mol/L sodium chloride (NaCl) were studied using the potentiodynamicgalvanostatic-potentiodynamic technique to measure film breakdown and repassivation potentials as well as protection temperatures. As expected, Cr is the key element determining resistance to crevice initiation, but a substantial Mo alloy content is required to achieve maximum film stability, especially at temperatures >60°C. Mo, not Cr, is the major element controlling crevice propagation and repassivation. If the protection temperature is accepted as the key indicator of overall alloy resistance, then the resistance increases in the order: Alloy 625 (UNS N06625) < C-4 (UNS N06455) < C-276 (UNS N10276) < C-22 (UNS N06022) ~ Alloy 59 (UNS N06059) ~ C-2000 (UNS N06200) < Alloy 686 (UNS N06686). More generally, this order could be written: high Cr-low Mo < low Cr-high Mo < high Cr-high Mo < high Cr-high (Mo+W). The individual influences of Mo and W appear to be inseparable and, while adding W improved the resistance, adding the equivalent amount of Mo could achieve the same improvement.

The temperature dependence of crevice corrosion initiation on titanium grade-2 has been investigated using a galvanic coupling technique. The film breakdown/repassivation transients indicate a temperature threshold, around 65°C, for the initiation of crevice corrosion. The number, size, frequency, and background current of these events increased when the temperature was increased from 65 to 80°C. Analysis of single transients suggests that the temperature also has an effect on the repassivation mechanism. Image analysis of corroded coupons reveals that crevice initiation and deeper penetration occur around the edge of the creviced area. Surface studies using electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy show oxide film flaws accompanied by water incorporation at temperatures above the 65°C threshold. Under creviced conditions, the occurrence of film flaws is the key process leading to the development of acidity and the initiation of crevice corrosion.

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The effects of iron content on the microstructure and crevice corrosion of Grade-2 titanium (Ti-2) were studied using a galvanic coupling technique combined with optical microscopy and secondary ion mass spectrometry (SIMS) imaging. This study reveals that iron content has a significant effect on the microstructure and crevice corrosion behavior of Ti-2. The grain size decreased significantly with increasing iron content. For a Ti-2 material with medium iron content, crevice corrosion readily initiated and the metal exhibited extensive intergranular attack that could be associated with the more reactive iron-stabilized β-phase within the α-phase matrix, as revealed by SIMS imaging. By contrast, Ti-2 materials with low and high iron contents showed suppressed crevice attack. The smaller surface area of available grain boundaries in Ti-2 of low iron content could account for this limited attack. For the material with high iron content, SIMS imaging suggests that some Ti x Fe intermetallic particles were formed. These particles may act as proton reduction catalysts and enhance crevice corrosion resistance via cathodic modification.