Monitoring the near-surface pH to probe the role of nitrogen in corrosion behaviour of low-temperature plasma nitrided 316L stainless steel
Monitoring the near-surface pH to probe the role of nitrogen in corrosion behaviour of low-temperature plasma nitrided 316L stainless steel
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DOI：
10.1016/j.electacta.2013.04.111
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发表时间：
2013-08-01
影响因子：
6.6
通讯作者：
Flis, J.
中科院分区：
文献类型：
--
作者：
Flis-Kabulska, I.;Sun, Y.;Flis, J.
不锈钢低温离子渗氮可提高其摩擦学性能和抗点蚀性能，但在酸性溶液中会激活阳极溶解。这项工作旨在确定阳极行为如何受到钢中氮的影响。研究了AISI 316L钢在415 ℃氮化后的电化学行为（最高17 at.% N）在酸化至pH 2.4的0.1 M Na 2SO 4 + 0.4 M NaCl溶液中进行检测。锑微电极用于测量接近样品表面的pH。结果发现，氮化层是耐点蚀在所有pH值的，但在pH值低于约3.5的阳极电流高于那些未经处理的钢。对于氮化钢，当阳极电流在活性区增加时，近表面pH增加，这显然是由于质子结合到NH 4+。渗氮钢在反向阴极扫描过程中发生了再活化，其特征是表面膜中氧化铬含量低。向溶液中注入NH 4 OH改善了钝化。热力学数据表明，pH值的升高使Fe 3 O 4、Fe 2 O3、Cr2 O3、FeCr 2 O 4、NiFe 2 O 4、MoO 42-和NO2-的生成成为可能。结果表明，渗氮钢的耐点蚀性是由于上述物种的形成而使早期点蚀易于再钝化的结果。(C)2013爱思唯尔有限公司保留所有权利。
Low temperature plasma nitriding of stainless steels improves tribological properties and pitting resistance, but it can activate anodic dissolution in acidic solutions. This work aimed at determining how anodic behaviour, can be affected by nitrogen present in the steel. The electrochemical behaviour of AISI 316L steel after nitriding at 415 degrees C (with up to 17 at.% N) was examined in solutions of 0.1 M Na2SO4 + 0.4 M NaCl acidified down to pH 2.4. An antimony microelectrode was used to measure pH close to the sample surface. It was found that the nitrided layer was resistant to pitting corrosion at all pH's, but at pH below about 3.5 anodic currents were higher than those on untreated steel. For nitrided steel the near-surface pH was increasing when anodic current was rising in the active region, evidently due to binding of protons into NH4+. Nitrided steel underwent reactivation during reverse cathodic sweeps which is characteristic of low content of chromium oxide in surface film. Injection of NH4OH into the solution improved the passivation. Thermodynamic data indicated that the accompanying pH rise enabled the formation of Fe3O4, Fe2O3, Cr2O3, FeCr2O4, NiFe2O4, MoO42- and NO2-. It is suggested that the pitting resistance of nitrided steel results from an easy repassivation of incipient pits due to the formation of the above species. (C) 2013 Elsevier Ltd. All rights reserved.