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 (FeO_xN_y) 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.

中文翻译：

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使用聚焦脉冲Nd：YAG激光在各种条件下对激光氮化的铁表面进行XPS研究

使用聚焦脉冲Nd：YAG激光在氮气气氛下对纯铁（Fe）表面进行激光氮化，并使用XPS分析了氮气压力，激光功率和重复激光发射次数对表面特性的影响。激光辐照表面由氮氧化铁的最表面层（FeO _x N _y）和下面的底层组成，这些底层主要包括氮化铁（Fe ₄N）。由于氮化物层的氧化，最顶层的表面层是后形成的层。在大气压下在氮气下，对应于原始氮化物层的底层的厚度急剧增加。增加激光发射的重复次数可将层厚度增加到5层，此后未观察到变化。此外，层厚度随着激光功率的增加而单调增加。通过脉冲激光辐射进行的氮化很可能主要是由比表面积的熔化和再固化以及其中的氮对流引起的。使用该假设可以适当地解释各种条件下的厚度变化。