Hot Corrosion of an Electrodeposited Ni-11 wt % Cr Nanocomposite under Molten Na[sub 2]SO[sub 4]–K[sub 2]SO[sub 4]–NaCl

A Ni–Cr nanocomposite with an average Cr concentration of was deposited onto nickel plate by simultaneous electrodeposition of Ni and Cr nanoparticles from a nickel sulfate bath. The nanocomposite consisted of a nanocrystalline Ni matrix and dispersed Cr nanoparticles with a mean size of . For comparison, two Ni–Cr alloys, one with similar Cr content and the other with much higher Cr content , were prepared using electro-arc melting. Hot corrosion testing under molten in air at showed that rapid formation of a continuous chromia-rich scale is essential for hot corrosion protection. This was the case only for the nanocomposite. Internal sulfidation was observed for arc-melted alloys, but not for the nanocomposite. The results demonstrate that it was not primarily the Cr content but the unique structure of the nanocomposite that was responsible for its superior hot corrosion resistance. The protection mechanism lies in the fast formation of a continuous chromia scale on the nanocomposite, due to the easy nucleation of chromia on both chromium nanoparticles and abundant nickel grain boundaries, and then fast linking of the nuclei as a result of enhanced diffusion of Cr through those grain boundaries.