Electrochemical behavior of alloy 22 processed by laser powder bed fusion (L-PBF) in simulated seawater and acidic aqueous environments

Abstract

Corrosion resistance of additively manufactured (AM) alloy 22 using Laser Powder Bed Fusion (L-PBF) was studied and compared with their wrought counterparts in 5 wt.% NaCl (pH ∼ 7.0) and 5 wt.% NaCl + 1.0 M HCl (pH ∼ -0.5) solutions. The l-PBF process parameters were selected from two extremes of a volumetric energy density (VED) process window. The effect of post-manufacturing processes on corrosion was also studied; these processes involved hot isostatic pressing (HIP) and solution treatment (ST). In 5 wt% NaCl, AM alloy 22 samples corrosion characteristics compared closely to wrought alloy 22 except when process parameters resulted in large pores, which acted as initiation sites for localized corrosion. In the acidic solutions, it was observed that the porosity and grain structure significantly affected corrosion performance. In general, the l-PBF-produced samples at higher VED (750 J/mm3) had lower porosity than samples produced at lower VED (188 J/mm3), which contributed to better corrosion performance. However, the lower ∑3 grain boundaries correlated to lower corrosion performance for all samples. HIP processing significantly lowered the porosity of the samples produced at lower VED and allowed for recrystallization of grain boundaries to increase the proportion of ∑3 grain boundaries, enhancing corrosion performance to near-wrought alloy 22 even in acidic solutions and at elevated temperatures.