温度变化对TiAlCN涂层耐蚀性和钝化膜性能的影响

Effect of Temperature on Corrosion Resistance and Passive Film Properties of TiAlCN Coatings

目的研究不同温度的3.5%(质量分数)NaCl溶液中TiAlCN涂层耐腐蚀性能的变化,并进一步探究温度对涂层表面钝化膜性能的影响。方法采用扫描电镜(SEM)、X射线衍射仪(XRD)、拉曼光谱仪和X射线光电子能谱仪(XPS)表征涂层的微观形貌和物相组成;通过动电位极化、电化学阻抗谱实验评估TiAlCN涂层的耐腐蚀性;进一步,先通过恒电位极化使涂层表面生成稳定的钝化膜,再利用X射线光电子能谱仪和Mott-Schottky测试探究钝化膜结构和半导体性质。结果TiAlCN涂层表面存在凹坑、颗粒和针孔,截面呈现出明显的柱状晶结构;涂层为面心立方结构,主要由TiC、TiN相组成;随着温度的升高,腐蚀电流密度及钝化电流密度增加,容抗弧直径减小,涂层的耐蚀性降低;TiAlCN涂层钝化膜的主要成分为Al_(2)O_(3)和TiO_(2),且二者含量随着温度的升高而减小。在20℃和80℃的温度条件下,TiAlCN涂层的钝化膜表现出n型半导体性质,且钝化膜的施主密度值从1.14×10^(16)cm^(-3)增加到3.27×10^(16)cm^(-3),钝化膜的保护能力降低。结论温度对TiAlCN涂层的耐腐蚀性有显著影响,高温会降低钝化膜的致密性及增加施主密度,使钝化膜的保护性降低,从而降低涂层的耐蚀性。

Mechanical parts are easy to fail under the action of high temperature and corrosion environment,physical vapor deposition coatings can be used to improve the surface performance of these parts and increase their service life.The corrosion resistance of coatings is related to their passivation performance.Thereinto,the temperature plays a key role in the passivation performance of the materials,thus tuning their corrosion rate.This work studies the change of corrosion resistance of TiAlCN coatings in the 3.5 wt.%NaCl solution at various temperature and further reveals the mechanism that how the temperature affects the corrosion resistance and passive film properties.Based on the cathode arc technique,a TiAlCN coating was deposited on a 316 stainless steel substrate with a dimension ofϕ8 mm×10 mm.In order to improve the binding force between the coating and the substrate,the coating was designed into a composite structure,and the bottom layer TiN and the transition layer TiAlN were successively deposited between the outer layer TiAlCN and the substrate.The micromorphology and phase constituent of the coating were detected by scanning electron microscopy(SEM),X-ray diffraction(XRD),Raman spectroscopy and X-ray photoelectron spectrometer(XPS).Open circuit potential,electrochemical impedance spectroscopy(EIS),dynamic potentiodynamic polarization,potentiostatic polarization and Mott-Schottky tests were carried out on the coating with platinum electrode as auxiliary electrode and saturated silver chloride electrode as reference electrode in 3.5wt.%NaCl solution by electrochemical workstation.The corrosion behavior of the coating and semiconducting properties of the passive film at different temperature(20,40,60,80)were studied.Among them,the℃polarization potential of the potentiostatic polarizations was selected in the passivation interval of the dynamic potential polarization curve.In the electrochemical experiment,the water bath crucible was utilized to maintain the electrolyte at the corresponding polarization temperature.In addition,X-ray photoelectron spectrometer was adopted to characterize the chemical distribution of the passive film formed on the TiAlCN coating.There were pits,particles and pinholes on the surface of the TiAlCN coating,with a typical columnar crystal structure.In addition,the coating was in a face-centered cubic structure,which composed of TiC and TiN phases.Meanwhile,the corrosion current density and the passivation current density increased,and the diameter of capacitive arc decreased,and the corrosion resistance of the coating decreased with the increase of temperature.The pitting potential of 316 stainless steel and the TiAlCN coating decreased with the increase of temperature,indicated that the pitting sensitivity of both increased.Meanwhile,the main components of the passive film were Al2O3 and TiO_(2),which decreased with the increase of temperature.As the temperature raised from 20 to 80,the passive film of the TiAlCN coating exhibited n℃℃-type semiconducting properties.Also,the donor density of the passive film increased from 1.14×10^(16) cm^(-3) to 3.27×10^(16) cm^(-3),indicated that the defects of the passive film increased,which was conducive to the erosion of corrosive ions,resulting in the worst protection ability of the passive film.Consequently,high temperature has a significant effect on the corrosion resistance of TiAlCN coatings by loosening the passive film and increasing the carrier density,which worsens the protectiveness of the passive film and the anti-corrosion capacity of the coating.