Rosales NiƱo, Oscar M.

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    Hydrogen transport behavior and phase decomposition of AISI-321 austenitic stainless steel via cathodic polarization
    (2007) Rosales NiƱo, Oscar M.; Uwakweh, Oswald; College of Engineering; CƔceres Valencia, Pablo G.; Sundaram, Paul A.; Department of Mechanical Engineering
    Room temperature cathodic polarization of AISI-321SS austenitic stainless steel in aqueous electrolytic H2SO4 with hydrogen recombination inhibitor (Na2HAsO4) generated phase decomposition on the subsurface layer of the AISI-321 stainless steel. X-ray diffraction patterns of the input-side of the samples permeated based on the Devanathan & Stachurski (DS) twin cell, and the freely suspended or wholly charged samples revealed three distinct FCC structures, two hexagonal structures, and a BCC structure. The FCC structures were identified as retained austenite, austenite with dissolved hydrogen, and faulted austenite. These were not observed on the exit-side of the permeated samples. The hexagonal structures were identified as faulted regions or the Īµ/ĪµH ā€“ phases (with or without hydrogen), while the BCC structure was identified as a martensitic phase. The permeation test showed the dependence of the overall permeation profile as a function of charging polarization current, with the rapid decay after peak permeation. This analysis of the transient stage was used to determine the apparent diffusivity which averaged as 5.89x10-11 cm 2 /s based on the slope method. Compared to the breakthrough method, the apparent diffusivity varied from 1.63x10-7 cm2 /s to 6.54x10-8 cm2 /s. Since the breakthrough time was almost independent of cathodic polarization current, the value of apparent diffusivity based on the slope method is taken to be more reliable. The decomposition of the austenitic phase accompanying the permeation implies therefore that the diffusivity is apparent.