N 2 /H 2 Non-thermal Transferred arc Plasma Nitriding Treatment of Stainless Steel at Atmospheric Pressure
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N2/H2 Non‑thermal Transferred arc Plasma Nitriding Treatment of Stainless Steel at Atmospheric Pressure Q. J. Guo1,2 · Y. J. Zhao1 · G. H. Ni1,3 · L. Li1 · Q. F. Lin1 · S. Y. Sui1 · H. B. Xie1 · W. X. Duan1 Received: 7 November 2019 / Accepted: 13 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In the paper, a novel metal surface nitriding method is presented by using an atmospheric pressure non-thermal transferred arc plasma technique. In the N 2/H2 plasma nitriding process, the surface of stainless-steel is treated by the arc root, which shows an irregular movement in a circle-like zone with about 5 mm diameter observed by high speed camera. The discharge has characteristics of high voltage and low current, and the gas temperature of the arc column plasma is only about 2900 K determined by the diatomic molecule N2+(B2Σ+u →X2Σ+g ) fitting method. It is found that the NH radical production in plasma plays an important role in the nitriding process. The thickness of nitrided layer can reach 60 μm after processing of 120 min under the optimal experimental conditions. The surface hardness of stainless-steel increased from 220 to about 1200 HV0.1 (Vickers hardness under the force of 0.1 kg) after plasma treatment. The treating saturation time for stainlesssteel surface hardness reaching to 1200 HV0.1 is around 9 min. Keywords Plasma nitriding · Non-thermal transferred arc · N2/H2 plasma · Atmospheric pressure
Introduction Nitriding for the steel surface produces Fe–N solid solution and nitride precipitates diffusion layer, which can significantly improve the performance of the base steel material, such as wear, fatigue and corrosion resistances. Nitriding technology applied in industry includes gas nitriding [1–3], salt bath nitriding [4, 5] and low-pressure plasma nitriding (referred to as ion nitriding) [6–9]. Among these nitriding technologies, ion nitriding has * G. H. Ni [email protected] Y. J. Zhao [email protected] 1
Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei 230031, People’s Republic of China
2
Anhui Huadong Institute of Photoelectric Technology, Wuhu 241002, People’s Republic of China
3
AnHui Province Key Laboratory of Medical Physics and Technology, Hefei 230031, People’s Republic of China
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Plasma Chemistry and Plasma Processing
been preferred in industrial application due to it having the advantage of environmentalfriendly and time-saving. However, ion nitriding technology requires a vacuum system which increase the complexity of process and the cost of production. Atmospheric pressure plasma technology has been attracted great attention in various application field because of the plasma source has the advantage of simple structure, high reactive radical production and the avoidance of complex vacuum system. Several approaches for metal surface nitriding have been proposed by using atmospheric pressure plasma technology. However, some problems still exist in the nitriding process by atmospheric
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