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 performance in service environments. The influence of both surface treatments and additive manufacturing-induced structural defects on oxidation processes is a subject that remains to be clarified. The present study investigates the surface changes of mechanically treated additively manufactured 316L stainless steel samples exposed to an oxidative environment. The as-prepared, ground and polished surfaces were examined before and after annealing at 550 °C and 1000 °C for 36 h, respectively. Furthermore, Mössbauer spectroscopy was identified as a valuable tool for distinguishing between metal-oxides when evaluated in comparison to X-ray diffraction. The observation revealed the presence of petal-shaped (Cr, Fe) 2 O 3 on the rough surface of the as-prepared sample that had been annealed at 550 °C. Meanwhile, the ground and polished samples contained only a surface layer of Fe 2 O 3 , which was detected by conversion electron Mössbauer spectroscopy. The growth of crystals was accompanied by the diffusion of Cr in the as-prepared sample after annealing at 550 °C. The diffusion of Cr and Mn was observed in the presence of octahedral (Mn, Cr) 3 O 4 crystals, which were evident in all samples annealed at 1000 °C. It has been discovered that the behaviour of diffusion and oxidation in regions close 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 of iron oxides, indicating the possibility of in-depth corrosion.