Mechanical behavior of Ni-Al2O3 nanocomposite coatings electroplated in the precence of organic compounds

In this study, a novel method was used to increase alumina nanoparticles content in nickel base composite coatings plated by pulse current. Methanol, ethanol and formaldehyde were partially added to the Watt’s solution as organic substances and nickel alumina nanocomposite coatings were produced adopted by simultaneous ultrasonic and magnetic homogenizing. After electroplating, the effect of these organic solvents was investigated by comparison of cross sectional observation of the coatings by field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray analysis (EDX). The hardness and wear behavior of electroplated nanocomposite coatings were evaluated by ball on disk test at room temperature and ambient air. Microstructures studies showed that the amount of incorporated nanoparticles in the coatings plated with the electrolyte without organic solvent is 2.1 wt. % and this amount increases with the addition of organic solvents. So that, the maximum amount of nanoparticles in this study (5.2 wt. %) is achieved by adding methanol. Surface hardness of the coatings plated with Watt’s solution was 301 Hv which increased to 485 Hv with adding methanol. Wear tests also showed that the addition of methanol increased the wear resistance twice more than the electrolyte without organic solvent. The microhardness investigation verifies this fact that increasing of reinforcement nanoparticles and coating’s microhardness due to adding methanol provides the oxide layer’s mechanical strength and creates the highest wear resistance in the plated nanocomposites.