Electrodeposition of nickel-based dispersion layers; study of particle incorporation and its influence on hardness and tribological performances

Abstract

Nano- to micro-scaled ceramic and polymeric particles were codeposited into Ni and NiP matrices by an electrochemical plating process using a Watts bath. The incorporation of the second phase particles was studied in relation to the dispersion bath stability. The particles in dispersion electrolyte were characterized through ultrasonic measurements of zeta potential and particle size distribution. A significant part of the thesis deals with codeposition of Ni-ZrO2 dispersion layers whereas content up to 10 vol. % of ZrO2 is obtained. Stability of ZrO2 particles in DI water and Watts bath was studied at different pH values. The effect of, and anions on the zeta potential of dispersed particles was investigated as well. High values of zeta potential lead to a good electrostatic repulsion within the dispersion. As a result, the particle agglomeration in the electrolyte slows down and the concentration of non-agglomerated particles rises resulting in an enhanced amount of particles incorporated in the electroplated Ni layers. These findings give a support to the diffusion transport of particles towards the cathode and disclaim some previous studies considering the electrophoresis as the only way of particle incorporation during the electro-codeposition. Plating parameters that might influence micro-structure and mechanical properties of Ni dispersion coatings were investigated and applied so, that a matrix of refined nickel grains with uniformly distributed particles (with agglomeration as small as possible) was obtained leading to layers of improved hardness and tribological performances, such as friction coefficient and wear resistance, compared to pure Ni coatings.<br />High range of current densities together with different streaming conditions such as rotating cylinder electrode geometry was studied.<br />Moreover, the influence of pulse plating sequences of different duty cycle was investigated as well. The optimum of the temperature, pH and the concentration of particles in the dispersion was found. SEM and EDX analysis of the codeposited layers were performed to characterise the coating morphology and to determine the particle concentration in the layers.