Exploring Corrosion Pathways in Wire-Arc Direct Energy Deposited Grade 2 Titanium in Chloride-Enriched Systems

Commercially pure grade 2 titanium (Cp-Ti) is important for marine and naval applications due to its excellent corrosion resistance. Additive manufacturing, especially Wire-Arc Direct Energy Deposition (WDED), enables the production of complex, large-scale Cp-Ti components but significantly alters the microstructure and properties due to thermal cycling. However, the corrosion behavior of WDED Cp-Ti in chloride-rich environments, relative to its complex microstructure, is poorly understood. This study investigates the onset and progression of corrosion in WDED Cp-Ti in HCl environments (1N-6N), revealing selective grain corrosion with evolving pitting morphology: globular at 1.25N-1.5N, pyramidal at 2N, and honeycomb-like at 6N. A novel corrosion mapping technique, combined with comprehensive electron backscatter diffraction (EBSD) analysis, reveals corrosion anisotropy within the microstructure. The grains oriented along the basal plane {0001} show superior corrosion resistance due to high in-plane atomic packing density, while prismatic planes {10 1̄ 1 ¯ 0} are more susceptible to corrosion. These findings demonstrate that optimizing crystal orientation with predominantly basal planes in bulk WDED Cp-Ti can significantly enhance its corrosion resistance. This can be achieved through advanced grain orientation techniques, such as in situ ultrasonic excitation of the melt weld pool and equal channel angular pressing of WDED parts.