Surface-nitriding treatment of steels using microwave-induced nitrogen plasma at atmospheric pressure

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• 作者：Shigeo Sato^a ; ^{s.sato@imr.tohoku.ac.jp} ; Yuuki Arai^a ; Noboru Yamashita^b ; Atsushi Kojyo^b ; Kenji Kodama^b ; Naofumi Ohtsu^c ; Yukio Okamoto^d ; Kazuaki Wagatsuma^a
• 关键词：Surface nitriding ; Plasma nitriding ; Microwave-induced nitrogen atmospheric pressure plasma ; X-ray photoelectron spectroscopy ; Glow discharge optical emission spectroscopy ; Depth profile
• 刊名：Applied Surface Science
• 出版年：2012
• 期刊代码：6_01694332
• 类别：ms
• 出版时间：15 July, 2012
• 卷：258
• 期：19
• 页码：7574-7580
• 文件大小：921 K

摘要

A rapid surface-nitriding system using microwave-induced nitrogen plasma at atmospheric pressure was developed for modifying iron and steel surfaces. Since the conventional plasma nitriding technique requires a low-pressure atmosphere in the treatment chamber, the population of excited nitrogen molecules in the plasma is limited. Accordingly, several hours are required for nitriding treatment. By contrast, the developed nitriding system can use atmospheric-pressure plasma through application of the Okamoto cavity for excitation of nitrogen plasma. The high population of excited nitrogen molecules induced by the atmospheric-pressure plasma allowed the formation of a nitriding layer that was several micrometers thick within 1 min and produced an expanded austenite iron phase with a high nitrogen concentration close to the solubility limit on the iron substrate. In addition, the nitriding treatment on high-chromium steel was performed by introducing a reducing gas such as NH₃ and H₂ into the treatment chamber. While the nitriding reaction did not proceed in a simple N₂ atmosphere due to surface oxidation, the surface reduction induced by the NH₃ or H₂ gas promoted the nitriding reaction at the surface. These nitriding phenomena characteristics of the atmospheric-pressure plasma are discussed in this paper based on the effects of the specimen temperature and plasma atmosphere on the thickness, the chemical states, and the nitride compounds of the nitrided layer as investigated by X-ray diffraction, glow-discharge optical emission spectroscopy, and X-ray photoelectron spectroscopy.