Duplex Ni-P-TiO 2 /Ni-P coatings were electrodeposited onto brass substrates. High phosphorus Ni-P coatings were plated as the inner layer to improve the corrosion resistance, while low phosphorus sol-enhanced Ni-P-TiO 2 coatings were deposited on the top to strengthen the mechanical property. The microstructure, morphology, mechanical property and corrosion resistance of coatings were investigated systematically. The results show that duplex coatings exhibit both excellent mechanical property

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... nd good corrosion resistance. The hardness was further improved from ~545 HV 50 of duplex Ni-P/Ni-P coating to ~622 HV 50 of duplex Ni-P-12.5mL/L TiO 2 /Ni-P coating, while the hardness of single Ni-P coating was only ~387 HV 50 . The corrosion resistance of duplex coatings improved significantly by adding a suitable amount of TiO 2 sol. Duplex Ni-P-12.5mL/L TiO 2 /Ni-P coating presented the highest corrosion resistance. However, adding excessive quantities of sol (more than 12.5mL/L) caused nanoparticle agglomeration and created a porous structure in the outer layer, deteriorating the properties of coatings.