Electrochemical nitriding of type 316 stainless steel (316 SS) in molten fluoride salt (LiF–KF, FLiK) contain-ing Li3N was investigated. Formation of chromium nitride CrN and iron nitride -Fex(x>8)N was confirmed.
Cyclic voltammogram measurements and electrolysis treatment were carried out using an Al–Li alloy ref-erence electrode at 873 K. After potentiostatic treatment at 1.0 V vs. Li/Li
+
for 100 min, the specimen was
characterized by SEM, XPS, EPMA, and XRD. SEM observation revealed that the initially smooth surface
changed into a rugged structure covered by a wrinkle structure about 1–2 m in width after electrolysis.
XPS analysis revealed that chromium nitride (CrN) was selectively formed at the surface layer. According
to the EPMA analysis, the treatment promoted nitrogen diffusion from the surface to a depth of 35 m.
CrN was formed from the surface to a depth of 2 m. It was determined that iron nitride -Fex(x>8)N was formed from there to a depth of 35 m as an inside diffusion layer, but neither Fe2N nor Fe4N was detected. Formation of CrN and -Fex(x>8)N was also confirmed by XRD measurement and XPS analysis.
The formation of chromium nitride and iron nitride was discussed in terms of thermodynamics
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