Effects of Iron Content on Microstructure and Crevice Corrosion of Grade-2 Titanium

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Abstract
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 TixFe intermetallic particles were formed. These particles may act as proton reduction catalysts and enhance crevice corrosion resistance via cathodic modification.