The effect of heat treatment on the electrochemical corrosion behavior of reactive plasma-sprayed TiN coatings

The effect of heat treatment on the corrosion behavior of reactive plasma sprayed TiN coatings in simulated seawater was investigated by electrochemical methods such as the corrosion potential-time curve (Ecorr − t), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and SEM, etc. The results showed that the corrosion potential of TiN coatings increased after heat treatment; the corrosion current of the TiN coatings after heat treatment (be hereafter referred to as HT-TiN) was 13.3% of the untreated coatings (be hereafter referred to as UT-TiN), and the polarization resistance of HT-TiN was 20 times of UT-TiN, which indicated that the heat treatment had significantly increased the corrosion resistance of the coatings. The corrosion behavior of the coatings was mainly local corrosion, and the local corrosion behavior mainly took place at the microdefects (crack and pores) of the coatings. The porosity of the coatings was reduced after heat treatment. The reason was that TiN reacted with O2 to form TiO2 and Ti3O during the heat treating, and volume expansion took place, which led to denser microstructure. The corrosion resistance of the coatings was therefore increased.

► The thickness of reactive plasma-sprayed TiN coatings can be up to 300 μm. ► Heat treatment enables the increase of corrosion resistance of TiN coatings. ► The corrosion process of the heat treated TiN coating was studied with aid of electrochemical impedance spectroscopy (EIS). ► TiO2 and Ti3O from the oxidizing reaction of TiN and O2 reduces the porosity.