Characterization Of The Effects Of Standardized Post-Processing Steps On The Localized Corrosion Resistance Of Laser Powder Bed Fused Inconel 718

As more industries look toward additively manufactured (AM) components to optimize lead times, cost of complexity, and more, those industries must evaluate the performance of materials produced by AM processes in comparison to their well-documented wrought or machined counterparts. The fact of the matter is that similitude is not a given. The technical focus in the AM world to date has been largely on the expected mechanical properties: fatigue, toughness, etc. Military, aerospace, and other sectors have identified the need to understand the effects of build defects, surface finish, and process parameters on the performance lifetime and survivability of AM parts. This concern should extend to materials degradation in the intended use environment and how the ulterior metallurgy formed during AM affects the expected alloy resistance to prudent corrosion mechanisms.

This investigation is focused on the effects of standardized post-processing typical for laser powder bed fusion (L-PBF) of Inconel 718 (I718). This includes stress-relief, hot-isostatic-pressing, solution-treating and aging via ASTM F3055-14 and AMS 2774. Prescribed solution-treating for I718 assumes metallurgy akin to wrought material. However, L-PBF processes create a discrete series of melt pools in the layer-wise assembly of components. Assumptions about the microstructure may obscure adverse effects of the standardized post-processing.

Cyclic potentiodynamic polarization (CPP) testing was employed to assess the effects of post-processing on the localized corrosion resistance of L-PBF I718. Initial characterization of the as-built condition elucidated the effect of build orientation. Subsequent CPP testing targets the change in localized corrosion resistance affected by post-processing. This is corroborated by metallographic examination of the resultant microstructure at each post-processing stage to determine if further optimization may be required to ensure I718’s inherent corrosion resistance.