High temperature oxidation and corrosion behaviour of Ni/Ni-Co-Al composite coatings

In the present study, Ni/Ni-Co-Al composite coatings were developed by a potentially simple, scalable, non-vacuum technique namely electrodeposition. These coatings were characterized for their microhardness, oxidation and hot corrosion behaviour. An increase in Co content in the matrix from 8 wt% to 70 wt% led to an increase in the Al particle incorporation from 12 wt% to 21 wt%. A change in the surface morphology of the coatings with variation in Co content was seen. The oxidation behaviour of the coatings was studied at temperatures in the range of 400 °C to 1000 °C. The influence of vacuum treatment on the high temperature behaviour of the coatings was also investigated. The intermetallic aluminide phase formation was observed in the temperature range of 600-800 °C and a homogenized structure was seen at 1000 °C. The oxidation rate in terms of weight gain was marginally lower for vacuum pretreated NiAl coating annealed at 1000 °C. A significant increase in the oxidation rate was exhibited by Ni-70Co-Al coating beyond 800 °C showing its poor oxidation behaviour. The characterization studies revealed the formation of stable alumina in the case of NiAl while, metastable alumina was observed in Ni-Co-Al coatings. The hot corrosion studies showed that Co rich Ni-Co-Al exhibited better resistance compared to Ni rich coatings. An optimum cobalt content of 30 wt% was desirable for high temperature oxidation and corrosion resistance.

► Aim is development of high temperature Ni/Ni-Co-Al coating through electrodeposition. ► Coatings characterized extensively for the microstructural changes. ► Evaluated for high temperature oxidation and hot corrosion behaviour. ► NiCo aluminide with optimum Co of 30 wt% suitable for high temperature applications.