Optical properties, surface composition and desorption of Stainless Steel (316L) studied from ambient temperature to 1000 K in vacuum

Stainless steels are widely used as structural materials due to their excellent corrosion resistance and fabricability. In some applications, in nuclear fusion reactors for instance, these materials may be exposed to harsh conditions, including high heat flux and ion bombardment in a vacuum environment, which can significantly affect their surface properties and composition. In this work, we investigate the temperature-dependent evolution of the surface composition and optical properties (reflectivity, emissivity) of stainless steel 316L. X-ray photoelectron spectroscopy analyses, temperature programmed desorption and reflectivity measurements in the visible/near-infrared range were performed on polished samples from ambient temperature to 1000 K. It was found that around 750 K, the initial Fe/Cr surface abundance of 90/10 changes to 35/55 following the onset of Cr and CrO desorption at 575 K, with Cr scavenging oxygen initially bound to Fe. In addition, Mn segregated at the surface and oxidized, while small amounts of metallic Ni segregated. Despite these modifications in surface composition, no significant change in reflectivity up to 900 K was observed. These results provide insight into the behavior of stainless steel under extreme conditions which is relevant for understanding its performance and durability in high-temperature applications.