Effect of hydrodynamic conditions of electrodeposition process on microstructure and functional properties of Ni-W/ZrO2 nanocomposites

Ni-W/ZrO2 nanocomposite coatings were electrodeposited in a system with a rotating disk electrode (RDE), which ensures constant and controlled hydrodynamic conditions. The influence of solution chemistry on the co-discharge kinetics of W(VI) and Ni(II) species from citrate solution have been studied. It was found that in the range of less negative cathode potentials both partial processes (deposition of tungsten and nickel) are controlled by charge transfer reaction, whereas with further increase of the cathodic polarisation the W(VI) electroreduction process becomes diffusion controlled. The addition of ceramic particles to the alloy plating bath changes cathodic polarisation, and thus chemical composition of the deposited Ni-W matrix. The effect of rotating rate of the steel RDE on the chemical composition and homogeneity of embedded zirconia nanoparticles in the Ni-W alloy matrix was investigated. The optimal hydrodynamic conditions for electrodeposition of homogeneous Ni-W/ZrO2 nanocomposites with enhanced functional properties were determined based on micro structural (morphology, phase composition, crystallite size), micromechanical (microhardness, Young's modulus), and tribological (wear resistant, friction coefficient) properties. The maximum incorporation of ZrO2 nanoparticles (about 4.5 wt%) was achieved at the disk cathode rotation speed of 300 rpm. Ni-W/ZrO2 coatings obtained in such hydrodynamic conditions were characterized by the highest hardness (9.1 GPa) and Young's modulus (205 GPa), but due to the significant brittleness revealed the lowest wear resistance. (C) 2016 Elsevier B.V. All rights reserved.