Abstract
A Ni–P–(sol)Al2O3 coating was prepared on the surface of Q235 steel by direct-current electrodeposition. This method was combined with sol-gel and electrodeposition technique, instead of the traditional nanopowder dispersion, to prepare highly dispersible oxide nanoparticle-reinforced composites. The effects of temperature, pH value, and current density and Al2O3 sol on the hardness of composite coating were investigated. The coating surface morphology and structure were characterized by scanning electron microscopy and energy dispersive spectroscopy, respectively. The corrosion resistance of coatings in the presence of intermediate layers was evaluated by electrochemical measurement in 3.5% NaCl solution by open-circuit potential measurement at room temperature. The hardness and wear resistance of the coating were measured by a microindentation instrument and friction wear machine, respectively. The results showed that Al2O3 sol can effectively improve Ni–P alloy coating structure and refine grain. When the bath temperature was 55°C, the pH value was 4.5, the amount of sol was 80 mL/L, the current density was 1 A/dm2, and the hardness of the nanosol coating was 569 HV. Compared with Ni–P, the friction coefficient increases slightly, but the wear rate was only 1.768×10−6 g·m−1. The corrosion resistance was also better than that of Ni–P coating.
Highlights
It is a challenge for traditional nickel coating, with the rapid development of modern industry, to meet the special requirements in some harsh conditions
The phosphorous nickel alloy coating obtained by electroless Ni–P plating is prone to pinholes and other defects on the surface, and the porosity and morphology will directly affect the corrosion resistance of the nickel-phosphorus alloy coating [3]
The polarization curve of the anode was measured at room temperature using a CS2350 electrochemical workstation, and the corrosion resistance of the coating was evaluated by a Tafel curve
Summary
It is a challenge for traditional nickel coating, with the rapid development of modern industry, to meet the special requirements in some harsh conditions. Direct current electrodeposition refers to the electrochemical deposition process of metals or alloys from their compound aqueous solution, nonaqueous solution or molten salt. It is the basis of the process of metal electrolytic smelting, electrolytic refining, electroplating, and electroforming. Ni-based alloys show several attractive properties, such as its high hardness [2], toughness, and relatively good corrosion resistance in air. For these reasons, they become the first choice of protective coating materials. As a widely used ceramic material, alumina is of high hardness and easy to be combined with matrix
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