Study on particle distribution, microstructure and corrosion behavior of Ni-Al composite coatings

摘要

Watt's baths containing different amounts of Al powder were used to electroplate the pure Ni and Ni-Al composite coatings. Surface morphology, microstructure of the samples and particle distribution in the coatings were studied using optical microscope, SEM, EDX and XRD. The results showed that the electroplated sample in the bath containing 40g·L~(-1) Al has the maximum particle and the best particle distribution. Evaluation of microstructures demonstrated that Al particles change the microstructure of Ni from coarse columnar to fine-granular structure due to providing new nucleation sites and stopping columnar growth of Ni grains. Corrosion measurements revealed that Ni-Al coatings have lower corrosion resistance than pure Ni probably due to formation of active-passive cells and weak bandings between Al particles and Ni substrate.