Abstract:The tribological properties of Ni-P/SiC nanocomposite coatings annealed at different temperatures (350-500 °C) were investigated in order to determine the optimal temperature needed to enhance their wear resistance as well as to reveal the underlying wear mechanisms. With increasing annealing temperature, the hardness of the annealed coatings gradually decreased from 8.2±0.5 to 7.1±0.6 GPa as a result of the Hall-Petch effect, nevertheless these values obtained were constantly higher than that of the as-plated coating (6.3±0.3 GPa) due to the formation of a hard Ni3P phase.Regarding to tribological properties, the Ni-P/SiC coating annealed at 350 °C presented a poorer wear resistance (6.1×10 -5 mm 3 /Nm) compared to the as-plated coating (3.9×10 -5 mm 3 /Nm) owing to a rougher original contact surface and the subsequent generation of nickel and iron oxides on the wear track. In contrast, coatings annealed at temperatures ranging between 400-500 °C exhibited the improved wear resistance (4.3×10 -5 -7.8×10 -6 mm 3 /Nm) attributable to their smoother surfaces and to the lubrication effect of H3PO4 arising from the tribochemical reaction between Ni3P and the environment. Overall, the Ni-P/SiC coating annealed at 500 °C containing the largest amount of Ni3P exhibited the lowest friction coefficient (0.51) and wear rate (7.8×10 -6 mm 3 /Nm).Keywords: Nickel-phosphorus; SiC; Electroplating; Tribology; Annealing. IntroductionProtective coatings have attracted scientific interest for decades due to their potential to increase resistance to wear and corrosion, which are estimated to account for 3-4% of the world's Gross [16] and CNTs [17] were incorporated into Ni-P coatings to enhance their mechanical and tribologicalproperties. As reported in Table 1, incorporation of reinforcing particles increases the hardness of Ni-P coatings, especially when SiC particles were used. Moreover, studies [18,19] have demonstrated that the incorporation of SiC particles in a Ni-P matrix is the most effective combination of cost and performance in industrial applications.Regarding Ni-P/SiC composite coatings, SiC particles with a size ranging between 0.5-6.0 µm was mostly used [20][21][22][23][24][25], while only a few studies investigated the use of nano-sized SiC particles (40-50 nm) [26][27][28][29][30][31][32]. However, it is worth noting that these studies investigated only the effects of SiC nanoparticles on the microstructures, corrosion resistance [26][27][28][29][30] and wear resistance of the as-plated coatings [31,32]. Therefore, there is still a large gap in the relationship between microstructure, mechanical and tribological properties of Ni-P/(nano)SiC coatings. In particular, the effects of postdeposition heat treatments on the tribological properties is still unexplored.In this study, SiC particles with a nanometric size were incorporated in Ni-P coatings, and the effects of different annealing temperatures on the microstructure, mechanical and tribological properties of the composite coatings was investigated and...

No abstract