Role of layered double hydroxide in enhancing wear and corrosion performance of self-lubricating hydrophobic Ni-B composite coatings on aluminium alloy

A layered double hydroxide reinforced nickel boride (LDH/Ni-B) hydrophobic composite coating was deposited on the A356 aluminium alloy surface by the electroless method. The anti-corrosion and anti-wearing performances were studied with varying amounts (0 to 5 wt%) of LDH in the nickel boride matrix. The composite coating with the highest water contact angle having a value of 120 degrees was observed for Ni-B containing 0.5 wt% of LDH. This could be attributed to the increased surface roughness offered by the LDH layers. Potentiodynamic polarization measurements in 3.5 wt% NaCl solution indicate a significant decrease in the corrosion current density (i(corr)) values for LDH added composite coating with a lowest of 3.96 x 10(-6) A/cm(2) for 0.5 wt% of LDH. This may be due to the combined effect of both coating hydrophobicity and feasibility for chloride ion intake by the ion-exchange mechanism of LDH. Improved wear resistance was obtained for composite coated aluminium with a minimum wear rate for 1% LDH added coating. Self-lubricating tribolayer formation in the presence of LDH gave higher wear resistance.