Size-dependency of corrosion behavior for TiN nanostructure coatings deposited by the PACVD method

Abstract

This paper evaluates the corrosion resistance of duplex treated AISI H11 tool steel. The duplex treatment involves cold wall plasma nitriding and plasma assisted chemical vapor deposition (PACVD). Plasma nitriding was carried out in a chamber including 25vol.% of N2 and 75vol.% of H2 at 500°C for 4h. PACVD treatment was performed in the same chamber containing Ar, N2, and H2 gases along with TiCl4 vapor for 4h at a chamber pressure of 3mbar, for different process temperatures of 470, 495, and 520°C. Field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and potentiodynamic polarization test in 3.5% NaCl solution were used to study the samples. The results indicate that samples coated with TiN at lower temperature exhibit a 10 times improvement in corrosion resistance relative to the coated samples at higher temperatures. It was found that the grain size is about 4–7nm which plays an important role in corrosion behavior. Furthermore, this study demonstrates that surface roughness increases by raising the deposition temperature of the PACVD treatment from 470°C to 520°C, leading to a lower corrosion resistance of the coated samples.