Layer-by-layer corrosion behavior of 316LN stainless steel with a gradient-nanostructured surface

A 316LN stainless steel with a gradient-nanostructured surface layer was fabricated by rotationally accelerated shot peening (RASP). The thickness of this gradient layer was about 210 mu m. Layer-by-layer electrochemical experiments confirmed that the layer of the gradient steel with the best corrosion resistance is found at a distance of 110 mu m from the surface. The nanostructures and pits generated by RASP produced two opposing effects on its corrosion resistance: the nanocrystals and nano-twins facilitate the formation of a thick, compact passive film which resists corrosion, whereas the pits tend to destroy it. The passive films formed on the pits and on the smoothly nanostructured areas were 5.5 nm and 13.9 nm thick, respectively.