Synthesis and electrochemical characteristics of Ta-N thin films fabricated by cathodic arc deposition

摘要

Ta-N thin films were deposited on AISI 317L stainless steel (SS) substrates by cathodic arc deposition (CAD) at substrate biases of —50 and -200 V. The as-deposited films were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX). The results show that stoichiometric TaN with hexagonal lattice (300) preferred orientation was achieved at the bias of -200 V. On the other hand, Ta-rich Ta-N thin film deposited at -50 V shows amorphous nature. According to the XPS result, Ta element in the films surface exist in bonded state, including the Ta-N bonds characterized by the doublet (Ta 4f_(7/2) = 23.7 eV and Ta 4f_(5/2) = 25.7 eV). Electrochemical properties of the Ta-N coated stainless steel systems were investigated using potentiodynamic polarization and electrochemical impedance spectroscope (EIS) in Hank's solution at 37℃. For the Ta-N coated samples, the corrosion current (i_(corr)) is two or three orders of magnitude lower than that of the uncoated ones, indicating a significantly improved corrosion resistance. Growth defects in the Ta-N thin films produced by CAD, however, play a key role in the corrosion process, especially the localised corrosion. Using the polarization fitting and the EIS modelling, we compared the polarization resistance (R_p) and the porosity (P) of the Ta-N coatings deposited at different biases. It seems that Ta-N film with comparatively lower bias (-50 V) shows better corrosion behavior in artifical physiological solution. That may be attributed to the effect of ion bombarding, which can be modulated by the substrate bias.