The Effect of Surfactant Concentration on Ni/Al₂O₃-hBN Hybrid Composite Coatings by Electro Co-Deposition

In the present work, Ni/Al₂O₃-hBN hybrid metal matrix composite (MMC) coatings were deposited from a modified Watt's type electrolyte containing nano-Al₂O₃ particles and hBN flakes by direct current (DC) plating method. It was aimed to develop optimum surfactant concentration for obtaining a non-agglomerated particles and high volume fraction of ceramic particles in the deposited Ni matrix. Since Ni coatings have low surface hardness for the applications that both corrosion and wear resistant are expected, Ni hybrid composite coatings were considered to overcome difficulties for dies, tools, automobile parts, microdevices and bearing applications. Al₂O₃ nano particles with average particle size of 80 nm were co-deposited with micron sized flake-like hBN particles and nickel matrix on the steel substrates. For the determination of the deposited layer properties micro hardness, wear resistance and friction coefficient were measured and scanning electron microscopy (SEM), equipped with EDS, was used for characterization. The hardness of the coatings was found to be 317–372 Hv depending on the particle volume fraction in the Ni matrix. The specific thickness and particle volume fraction in the deposited composite coatings were measured about between 50–200 μm and 0.02–0.12, respectively. The effect of ceramic particles in the nickel matrix on the tribological performances of the hybrid coatings produced with different surfactant concentrations was investigated. The tribological tests were performed by a reciprocating ball-on disk apparatus sliding against M50 steel ball (Ø 10 mm). All the friction and wear tests were performed under the unlubricated conditions at room temperature and in the ambient air (relative humidity 55–65%). The results showed that the wear rate of the nano composite coatings could be reduced to such low values of 20 × 10⁻⁴ mm³/Nm.