Corrosion Behavior of Additively Manufactured Ti-6Al-4V Alloy Annealed at 650 °C in 3.5 wt% NaCl Solution

The effects of heat treatment on the residual stress and corrosion behavior of additively manufactured Ti-6Al-4V alloys were analyzed and compared with those of subtractively manufactured Ti-6Al-4V alloys. Heat treatment was performed on the samples at 650 °C for 2 h, followed by air cooling to reduce their residual tensile stress. Microstructural observations, hardness measurements, and residual stress measurements were then performed. Potentiodynamic polarization tests were also performed in 3.5 wt% NaCl solution to measure the corrosion potential, corrosion rate, and pitting potential. There were no differences in the residual stresses before and after heat treatment in the subtractively manufactured alloy. In contrast, in the additively manufactured alloy, the tensile stress before heat treatment changed to compressive stress after heat treatment. Heat treatment resulted in minor decreases in the corrosion potentials of both alloys, whereas the corrosion rates increased slightly after heat treatment. The pitting potential of the subtractively manufactured and additively manufactured alloys was not significantly influenced by heat treatment. However, the repassivation potential increased slightly in the subtractively manufactured alloy after heat treatment, whereas it increased significantly in the additively manufactured alloy. The potentiostatic polarization test results confirm that the number of metastable pitting events was remarkably reduced by heat treatment in the additively manufactured alloy.