Abstract
Duplex Ni-P-TiO2/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-TiO2 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 and good corrosion resistance. The hardness was further improved from ~545 HV50 of duplex Ni-P/Ni-P coating to ~622 HV50 of duplex Ni-P-12.5mL/L TiO2/Ni-P coating, while the hardness of single Ni-P coating was only ~387 HV50. The corrosion resistance of duplex coatings improved significantly by adding a suitable amount of TiO2 sol. Duplex Ni-P-12.5mL/L TiO2/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.
Highlights
As one of the most widely used coatings in industry, Ni-P coatings have attracted great attention due to their unique properties, such as shinning surface, high wear resistance and excellent corrosion resistance 1-3
TiO2 sol was prepared as reported in the previous papers . 15-18 For comparison purposes, a duplex Ni-P/Ni-P coating without adding sol was prepared with the identical plating parameters
After depositing low P Ni-P coating on the high P Ni-P layer, some diffraction peaks derived from the brass substrate could not be detected, which can be attributed to the increase of coating thickness
Summary
As one of the most widely used coatings in industry, Ni-P coatings have attracted great attention due to their unique properties, such as shinning surface, high wear resistance and excellent corrosion resistance 1-3. We recently developed a novel sol-enhanced plating method 12 This method which combines the sol-gel process with electrodeposition can lead to a highly distribution of oxide nanoparticles in the coating matrix, resulting in significantly improved mechanical properties. Based on this new technology, electroless double-layered Ni-P-XZrO2/Ni-P coatings with different phosphorus (P) contents have been prepared on stainless steel[13] and AZ31 magnesium alloy[14], respectively. These duplex coatings may find a promising industry applications as they exhibit excellent mechanical property and high corrosion resistance. The microstructure, morphology, mechanical property and electrochemical property of coatings were systematically investigated
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