XPS study of a laser‐nitrided iron surface using a focused pulsed Nd:YAG laser under various conditions

Abstract

Laser nitridation of a pure iron (Fe) surface was conducted using a focused pulsed Nd:YAG laser under a nitrogen atmosphere, and the effects of nitrogen gas pressure, laser power, and repetition number of laser shots on the surface characteristics were analyzed using XPS. The laser‐irradiated surface consisted of the topmost surface layer of Fe oxynitride (FeOxNy) and the underlayer beneath, which mainly comprised Fe nitride (Fe4N). The topmost surface layer is a post‐formed layer due to the oxidation of the nitride layer. The thickness of the underlayer corresponding to the original nitride layer drastically increased under nitrogen gas at atmospheric pressure. Increasing the repetition number of laser shots enhanced layer thickness up to 5 shots, after which no change was observed. Moreover, the layer thickness increased monotonically with increasing laser power. Nitridation through pulsed laser irradiation was likely predominated by the melting and resolidification of a specific surface area, as well as the convection of nitrogen therein. Thickness variation under various conditions can be explained appropriately using this assumption.