N.D. Chronopoulou, A.M. Routsi, E. Siranidi, E.A. Pavlatou
7th Pulse Plating Seminar-East Forum (2016), 3-4 March, Baden, Austria (oral)
Electrolytic co-deposition is one of the most widely-used methods for preparing metal/alloy coatings and nanostructured composite coatings. The development of production technology of composite electro-coatings such as metal matrix reinforced with nano-particles, is primarily aimed at improving the mechanical, tribological and corrosion behavior of metal matrix. Conventionally, ceramic powders such as alumina, silicon carbide, and diamond were used as reinforcing materials for Ni-based nanocomposite coatings. Recently, carbon nanotube (CNT) has been applied as a new reinforcing agent for composite coatings due to its excellent mechanical properties and high thermal conductivity. Ni matrix composites reinforced by carbon nanotubes have been studied for both improved mechanical properties and for potential applications as anticathode material in dye sensitized solar cells. This study concerns the electrolytic codeposition of hybrid multi-walled carbon nanotubes (MWCNTs)/Al2O3 with nickel by applying both direct and pulsed current conditions, in presence and absence of additive in the bath. The particles were supplied by the group of Prof. Jinbo Bai from the Lab. MSSMat of Ecole Centrale Paris. In this work a Watts type bath, with and without additive was used with a constant pH=3.5 and temperature 50±1°C. The electrodeposition of Ni/ MWCNT-Al2O3 composites was carried out on a rotating disk electrode (RDE). Pure Ni deposits were also produced under the same experimental conditions, as reference state for comparison reasons. The surface morphology, the crystallographic orientation and the grain size of nickel matrix were investigated as a function of the type of applied current (e.g. direct or pulse) and the presence of additive. The imposed current pulses ranged between 1 up to 1000 Hz. The surface morphology and structural characteristics of all coatings were investigated by using electron microscopy SEM-EDS, while the predominant crystallographic orientation of crystallites Ni studied by XRD. By utilizing a ball on disc tribometer under dry sliding conditions the wear behavior of the composite coatings were investigated. The roughness of the surface of the coatings as well as of the morphology of wear track was studied by using a laser profilometer. Micro-Raman spectroscopy has been utilized to characterize the composition of the composites, the wear tracks as well as of the crosssectional profile of the coatings. The application of pulse current at high frequencies in combination with the presence of additive, leads to composite coatings with a relatively uniform distribution of MWCNTs-Al2O3 particles and coherent structure into the metallic nickel matrix, exhibiting an increased resistance to sliding friction. The simultaneous presence of MWCNT-Al2O3 particles in the bath and the application of high current pulses results to the production of nano-structured coatings with a mixed preferred crystalline Ni orientation ([110]+[211]) compared to the pure Ni coatings produced under the same electrolytic conditions that presented a [110] texture.