Electrodeposition of Ni–Mo and Ni–Mo-(nano Al 2 O 3 ) multilayer coatings

Abstract

In the present work, multilayer Ni–Mo–Al₂O₃ and Ni–Mo coatings were fabricated on the low-carbon steel using pulse electrodeposition technique from a citrate-ammonia bath. The coatings with different number of layers (32, 128 and 512) were electrodeposited by the periodic alteration of duty cycle (between 20 and 90%) at a constant frequency of 400 Hz and an average current density of 6 A dm⁻². The corrosion resistance of the coatings was estimated using potentiodynamic polarisation and electrochemical impedance techniques and wear properties was also evaluated using pin-on-disk wear test. Potentiodynamic polarisation and electrochemical impedance in 3.5 wt-% NaCl solution showed that 128-layer nanocomposite coatings had the highest corrosion resistance. By increasing the number of the layers in Ni–Mo coatings, their hardness was improved from 563 ± 20 Hv_0.1 to 714 ± 42 Hv_0.1, while the wear rate was decreased from 9.87 to 5.16 μg N⁻¹ m⁻¹. The addition of nanoparticles showed favourable impacts on the coatings hardness and wear properties.