Thermally sprayed multi-principal element Cr40Co40Ni20 coatings – Oxidation upon coatings' build-up and electrochemical corrosion

Thermally sprayed Cr40Co40Ni20 coatings were produced by high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF). The phases formed upon coatings' build-up were sensitive to oxidation at high temperatures, leading to the formation of various oxygen-rich compounds such as chromia and spinel. Chromia tended to be formed at the inner layer, in contact with the metal, and the spinel forming the outer layer. HVAF coatings suffered much less oxidation compared to the HVOF coatings. The pronounced Cr-depletion at the metallic and oxygen compounds caused by formation of spinel and oxide upon deposition of coatings created regions susceptible to readily corrode in chloride-rich electrolyte.