Abstract
In this research, the effect of heat treatment on the hardness and wear resistance of the composite duplex electroless coating of Ni-P/Ni-B containing BN nanoparticles has been investigated. For this purpose, a 15-micron Ni-P electroless coating and a 10-micron Ni-B-BN electroless coating were applied on the surfaces of samples. The coated samples were heat treated for one hour at 300, 400 and 500 °C. The effect of heat treatment on the morphology, hardness and wear behavior of the coatings was studied by the SEM, XRD, and pin-on-disc wear test. Tafel polarization test showed that the presence of the Ni-P electroless coating improves the corrosion resistance of the duplex coating. Moreover, the microhardness of coating was evaluated before and after the heat treatment via the Vickers microhardness testing machine to evaluate the effect of heat treatment temperature on the hardness of the samples. The results indicated that the produced coating morphology is cauliflower-shaped. The heat treatment at 400 °C creates the nano-crystalline structure, thereby increasing the hardness and wear resistance of the coating due to its change from the amorphous to crystalline structure and the production of the Ni₃B hard phase. The Tafel polarization test revealed that the Ni-P layer improves the corrosion resistance of the two-layer composite coating.

Key words
nickel-boron electroless coating, heat treatment, corrosion, hardness, wear resistance

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