Electrochemical study of laser nitrided and PVD TiN coated Ti–6Al–4V alloy: the observation of selective dissolution

Abstract

Several techniques are considered to improve the tribological and corrosion properties of the Ti–6Al–4V alloy. One of the promising techniques is the duplex treatment. In the present study, electrochemical testing of a duplex treated Ti–6Al–4V alloy is considered. The duplex treatment is carried out in two steps. In the first step, the alloy surface is laser nitrided while in the second step, the nitrided alloy surface is PVD TiN coated. Corrosion rates and electrochemical properties of the treated surfaces are investigated using polarization techniques. A comparison of the electrochemical response of the duplex treated, PVD TiN coated, and untreated workpieces is made. X-Ray diffraction spectroscopy (XRD), energy dispersive spectrometry (EDS) and scanning electron microscopy (SEM) are carried out to examine the coating layer, pit morphology and elemental structures due to duplex treatment and controlled electro-oxidation. It is found that the duplex treated workpiece surface is more resistant to corrosion as compared to TiN coated and untreated surfaces. Among the three metals contained in the alloy, aluminum is found to selectively dissolve in large proportion in solution during oxidation.