The corrosion behavior of Ni-Cu gradient layer on the nickel aluminum-bronze (NAB) alloy

The gradient Ni-Cu layer on nickel aluminum-bronze alloy was obtained by the thermal diffusion process. The corrosion resistance was improved due to the formation of protective film, consisted of Ni(OH) 2 and Cu 2 O. Although the Ni-Cu layer exhibited local corrosion with uniform corrosion and pitting corrosion simultaneously during the immersion test, the pitting growth was depressed because of the gradient distribution of Ni and Cu. The relieving driving force for galvanic corrosion between outer passive layer and bare Ni-Cu in the pitting was the main factor, which was caused by the decreasing interface potential drop.