Effect of Post-processing on Corrosion Behavior of LPBF Built Inconel 718 Alloy

In the present study, the impact of corrosion behavior on laser powder bed fusion (LPBF) built Inconel 718 (IN718) was examined in 3.5 wt.% NaCl solution with an increasing immersion time of 1 day and 5 days. The influence of post-processing on corrosion behavior of as-built (AB) specimens such as solution treatment annealing (STA), and hot isostatically pressed (HIP) with double aging (HIP + DA) were studied in detail. The electrochemical measurements were carried out using open circuit potential (OCP), potentiodynamic polarization curve, and electrochemical impedance spectroscopy (EIS). The HIP + DA specimen exhibits lower LAGB (low angle grain boundary), HAGB (high angle grain boundary), and reduced porosity than STA, and AB. A drastic microstructural change has occurred from columnar (as-built) to equiaxed grains (HIP + DA). The as-built specimen immersed for 5 days, exhibit the highest corrosion rate, indicating the rapid dissolution of the oxide layer in the trade-off with HIP + DA. Electrochemical analysis revealed that the HIP + DA has higher impedance at a lower frequency both for 1 day and 5 days of immersion, ensuring a candidate material for marine application. The HIP + DA specimen exhibited improved corrosion performance upon exposure to corrosive media. After corrosion, the as-built specimen shows more pits than HIP + DA specimens.