Comprehensive Electrochemical Studies on Nanolayered Multilayered Ti/TiN and TiAl/TiAlN Coatings Deposited on Ti6Al4V Substrates

Corrosion resistance properties of Ti/TiN and TiAl/TiAlN nanolayered multilayered coatings deposited on Ti6Al4V alloy substrates by unbalanced magnetron sputtering were investigated. The coatings contain a bi-layer thickness of Ti/TiN or TiAl/TiAlN ∼3.5 nm/4 nm and the total thickness of the coating is ∼9 µm. Corrosion properties of the coatings were investigated using electrochemical impedance spectroscopy (EIS) for 30 d while immersed in 3.5 wt% NaCl solution. EIS investigation of the coatings showed that the corrosion occurred due to the penetration of electrolyte and oxygen through the micro/nanopores present in the coatings. It was found that the TiAl/TiAlN coating offered corrosion protection superior to that of the Ti/TiN coating during the immersion study. Potentiodynamic polarization studies revealed that both coatings showed passive behavior. Formation of a passive film on the coated surface during polarization enhanced the barrier properties of the coatings and provided anodic protection to the underlying alloy.