Characterization and corrosion behavior of electroless Ni-Mo-P/Ni-P composite coating in CO2/H2S/Cl- brine: Effects of Mo addition and heat treatment

The electroless Ni-Mo-P/Ni-P composite coating was applied on N80 carbon steel, and the effects of Mo addition and heat treatment on the corrosion resistance enhancement in CO2/H2S/Cl- brine were studied by electrochemical measurements and surface analysis techniques. The Mo addition in the as-deposited Ni-P coating causes the microstructural transformation from amorphous to crystalline due to the reduced P content, thereby suffering severe corrosion. The impaired corrosion performance of as-deposited Mo-incorporated coating is also originated from the absence of the oxide film on the coating surface. Nonetheless, the heat-treated Ni-Mo-P/Ni-P coating exhibits desirable corrosion resistance, which is reflected by the outstanding corrosion inhibition efficiency (eta = 96.1%). Heat treatment facilitates the formation of Ni4Mo phase and more importantly, the growth of an oxide film consisting of nickel and molybdenum oxides (H2S-immuned MoO3) with better passivation properties, which accounts for the remarkable corrosion resistance improvement.