Corrosion-erosion behavior of TiN-coated stainless steels in aqueous slurries

The corrosion-erosion resistance of TiN-coated AISI 304 and AISI 420 stainless steels in aqueous slurries was studied. TiN films with a thickness of 0.6 μm were obtained by using the pulsed-arc plasma-assisted physical vapour deposition technique. The corrosion-erosion experiments were performed in a test machine in which the impingement velocity, impact angle, concentration of solids and pH of the solution were controlled. Polarization curves were simultaneously obtained to relate the electrochemical effects to the erosive wear mechanisms. The slurry used consists of quartz particles suspended in a mixture of sulphuric acid solution and 3.5% NaCl, with a pH value of 0.2. Measurement of critical and passive current densities showed that the behavior of coated materials differed according to substrate, but in a general way increasing impact velocity and changing from normal to grazing incidence led to a reduction in resistance to corrosion-erosion and liquid impingement corrosion. Surface analysis by SEM revealed formation of cracks in the coating and plastic deformation in both the substrate and the coating, especially when the mean impact velocity exceeded a critical value between 6.9 and 8.6 ms−1. Additionally, intergranular corrosion was observed in some specimens.