Corrosion Failure Mechanism of NiCoCrAlY/AlSiY Composite Coatings in Alternating High and Low Temperature Marine Environments

Abstract

To investigate the corrosion damage and degradation mechanism of NiCoCrAlY/AlSiY composite coatings in alternating high and low temperature marine environments, the corrosion damage behavior of NiCoCrAlY/AlSiY composite coatings was studied by designing the alternating high and low temperature oxidation and high temperature oxidation-acidic salt spray alternating tests. Results showed that after 50 cycles of alternating high and low temperature oxidation at 750 ℃, the coating underwent oxidative erosion in the oxidation test, but the integrity of the surface structure was not damaged. After the experiment, the weight of the alloy increased by only 3.87 mg/cm2, indicating that the coating effectively inhibited the diffusion of oxygen into the interior and prevented the substrate from oxidative attack. During the 50 cycles of alternating high temperature oxidation and acidic salt spray tests, the NiCoCrAlY/AlSiY composite coating experienced severe corrosion degradation, and the alloy weight increased to as high as 13.52 mg/cm2 by the end of the test. Due to long-term salt spray erosion, the oxide layer structure weakened, leading to surface loosening, the formation of corrosion pits, and even peeling. As the number of alternating cycles of high temperature oxidation-acidic salt spray increased, the critical reaction causing coating damage shifted from oxidative erosion to thermal corrosion. The chlorine, generated from the eutectic reaction of the mixed salt, acted as a catalytic carrier and accelerated the growth of oxidation products, demonstrating that the NiCoCrAlY/AlSiY composite coatings had weak corrosion resistance under alternating high temperature oxidation-acidic salt spray environments.

Keywords

• nicocraly/alsiy composite coating; marine environment; high and low temperature oxidation alternation; high-temperature oxidation-acidic salt spray alternation