Impact of surface roughness and additive manufacturing-induced structural defects on oxidation of 316L stainless steel

The understanding of surface oxidation in additively manufactured metals is a critical aspect of their performancein service environments. The influence of both surface treatments and additive manufacturing-inducedstructural defects on oxidation processes is a subject that remains to be clarified. The present study investigatesthe surface changes of mechanically treated additively manufactured 316L stainless steel samplesexposed to an oxidative environment. The as-prepared, ground and polished surfaces were examined before andafter annealing at 550 ◦C and 1000 ◦C for 36 h, respectively. Furthermore, M¨ossbauer spectroscopy was identifiedas a valuable tool for distinguishing between metal-oxides when evaluated in comparison to X-raydiffraction. The observation revealed the presence of petal-shaped (Cr, Fe)2O3 on the rough surface of the aspreparedsample that had been annealed at 550 ◦C. Meanwhile, the ground and polished samples containedonly a surface layer of Fe2O3, which was detected by conversion electron M¨ossbauer spectroscopy. The growth ofcrystals was accompanied by the diffusion of Cr in the as-prepared sample after annealing at 550 ◦C. Thediffusion of Cr and Mn was observed in the presence of octahedral (Mn, Cr)3O4 crystals, which were evident in allsamples annealed at 1000 ◦C. It has been discovered that the behaviour of diffusion and oxidation in regionsclose to structural defects exerts a substantial influence on the final surface morphology and element composition.Thus, the ground sample that was subjected to annealing at 1000 ◦C contained elevated concentrations ofiron oxides, indicating the possibility of in-depth corrosion.