Xu Jiang, Peng Shuang, Li Zhengyang, Jiang Shuyun, Xie Zong-Han, Munroe Paul
Department of Material Science and Engineering, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, PR China.
Department of Material Science and Engineering, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, PR China.
Ultrason Sonochem. 2021 Mar;71:105406. doi: 10.1016/j.ultsonch.2020.105406. Epub 2020 Dec 6.
To alleviate the cavitation damage of metallic engineering components in hydrodynamic systems operating in marine environments, a NbN nanoceramic coating was synthesized on to a Ti-6Al-4V substrate via a double cathode glow discharge technique. The microstructure of the coating consisted of a ~13 μm thick deposition layer of a hexagonal δ'-NbN phase and a diffusion layer ~2 μm in thickness composed of face-centered cubic (fcc) B1-NaCl-structured (Ti,Nb)N. The NbN coating not only exhibited higher values of H/E and H/E than those measured from NbN coatings deposited by other techniques, but also possessed good adhesion to the substrate. The cavitation erosion resistance of the NbN coating in a 3.5 wt% NaCl solution was investigated using an ultrasonic cavitation-induced apparatus combined with a range of electrochemical test methods. Potentiodynamic polarization measurements demonstrated that the NbN coated specimens demonstrated both a higher corrosion potential (E) and lower corrosion current density (i) than the uncoated substrate. Mott-Schottky analysis, combined with the point defect model (PDM), revealed that, for a given cavitation time, the donor density (N) of the passive film on the NbN coating was reduced by 1 ~ 2 orders of magnitude relative to the uncoated Ti-6Al-4V, and the diffusivity of the point defects (D) in the passive film grown on the NbN coating was nearly one order of magnitude lower than that on the uncoated substrate. In order to better understand the experimental observations obtained from Mott-Schottky analysis and double-charge layer capacitance measurements, first-principles density-functional theory was employed to calculate the energy of vacancy formation and the adsorption energy for chloride ions for the passive films present on both the NbN coating and bare Ti-6Al-4V.
为减轻海洋环境中运行的流体动力系统中金属工程部件的空化损伤，通过双阴极辉光放电技术在Ti-6Al-4V基体上合成了NbN纳米陶瓷涂层。涂层的微观结构由一个约13μm厚的六方δ'-NbN相沉积层和一个约2μm厚的由面心立方（fcc）B1-NaCl结构的（Ti，Nb）N组成的扩散层。NbN涂层不仅表现出比通过其他技术沉积的NbN涂层更高的H/E和H/E值，而且与基体具有良好的附着力。使用超声空化诱导装置结合一系列电化学测试方法，研究了NbN涂层在3.5wt%NaCl溶液中的抗空蚀性能。动电位极化测量表明，NbN涂层试样比未涂层的基体具有更高的腐蚀电位（E）和更低的腐蚀电流密度（i）。Mott-Schottky分析结合点缺陷模型（PDM）表明，对于给定的空化时间，NbN涂层上钝化膜的施主密度（N）相对于未涂层的Ti-6Al-4V降低了1~2个数量级，并且在NbN涂层上生长的钝化膜中点缺陷的扩散率（D）比未涂层基体上的低近一个数量级。为了更好地理解从Mott-Schottky分析和双电荷层电容测量中获得的实验观察结果，采用第一性原理密度泛函理论计算了NbN涂层和裸露的Ti-6Al-4V上存在的钝化膜的空位形成能和氯离子的吸附能。
