Performance Characteristics of Corrosion Resistant Black Coatings

A new trivalent chromium black plating based on trivalent chromium and cobalt metal has been optimized both in the as plated as well as annealed conditions. The annealed coatings exhibited high hardness, good corrosion resistance and optical properties. XRD and SEM investigations confirmed the formation of intermetallic phases of Cr-Co-P which induced mechanical properties of the coatings. The corrosion resistance characteristics of coatings have been evaluated in 3.5% NaCl using potentiodynamic polarization and A.C impedance measurements. The black coatings offered a good absorption and emission properties.