True active surface area as a key indicator of corrosion behavior in additively manufactured 316L stainless steel
MATERIALS & DESIGN(2024)
Abstract
Laser powder bed fusion (LPBF) additively manufactured (AM) 316L stainless steels (SS) possess much more complex surfaces than their wrought counterparts which affects the corrosion behavior. Surface roughness, a typical metric for assessing corrosion of conventionally manufactured metals, is often ineffective as an independent parameter in characterizing corrosion of the AM metals for their higher surface roughness ranging from 5 to 50 mu m. This study experimentally shows that the true active surface area (ATA) is a proper parameter for quick assessment of localized corrosion response of AM 316L SS. Through the potentiodynamic polarization testing on surrogates under full immersion in 0.6 M NaCl solution, the pitting corrosion susceptibility was evaluated. While no consistent correlation to surface roughness was displayed, the pitting breakdown potential (Ep) showed a clear statistical trend at 1/A0.5TA. In addition, normalization of the polarization resistance with the ATA reveals the corresponding surface roughness did not significantly affect the change in open-circuit corrosion phenomenon. This correlation fits well with a previously reported stochastic pitting model on metal surfaces. The results suggest that the importance of ATA as a predictor for predisposition to corrosion in AM 316L SS extends far beyond what has been established for wrought materials.
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Key words
True active surface,Additive manufacturing,316L stainless steel,Surface roughness,Corrosion
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