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 ~3.5/4 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 days 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/nano pores 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 behaviour. 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.