Trends in corrosion resistance of electroless Ni-B-Mo coatings

Ternary Ni-B-Mo coatings are prepared using various coating compositions through the chemical deposition method. AISI 1040 steel specimens are used as the substrate to develop coated layers. The chemical solution compositions are varied to understand their impact on coating behaviours. A three-electrode-based potentiostat is applied to determine corrosion behaviour. The experiments are carried out in a 3.5 wt. % NaCl solution. All the coated surfaces displayed a surface morphology resembling cauliflower. The coated layer thickness increased from 13 to 42 µm. The boron content increased with NaBH4 concentration, resulting in an enhancement in corrosion behaviour. The electroless Ni-B coatings usually become rough, leading to corrosion resistance deterioration. While the molybdenum concentration does not significantly impact boron content, it deteriorates the corrosion resistance at its higher concentrations due to rougher surface morphology. The performance against corrosion at level 1 is worst due to cracked surface morphology, while the same performance is best at level 3 concentrations.