Results of electrocodeposition of gold matrix composite coatings with carbon-based materials are reported, namely ultradispersed diamonds (UDD) and multiwalled carbon nanotubes (MWCNT). Pure gold and gold composite coatings were prepared from a gold sulphite electrolyte with bath loads from 5 to 20 g/l (UDD bath) and from 0.1 to 5 g/l (MWCNT bath). The resulting composites are characterized in terms of carbon content, particle distribution, and their bonding to the matrix, surface morphology, and the influence of particle loading in the electrolyte on matrix microstructure. Vickers hardness, friction, and wear behavior were investigated and are discussed in terms of microstructure characterization. Some notable improvements in the performance of the composites were observed with regard to application as sliding contacts.
The effect of ultrasonics on filling properties has been studied by Ni electroplating from a sulphamate electrolyte in high aspect ratio grooves. Experiments were carried out with two different modes of ultrasound: a) 25 kHz ultrasound with an effect of 225 W directed perpendicular to the substrate surface; b) ultrasonic standing waves of 100 kHz and 400 kHz parallel to the substrate surface. It was found that both methods improve filling in grooves that are between 0.35 and 1 mm wide with aspect ratios between 0.6 and 3, compared to electroplating with conventional agitation. Under the investigated conditions, the 400 kHz standing wave parallel to the surface was most efficient to improve filling of grooves.
The electrodeposition of nickel-iron-alloys from a sulfate electrolyte with different additives ist described. As deposited alloys contained between 10 and 36 % of iron and were charaterized by hardness, grain size and lattize parameter. The thermal stability of the different alloys by exposing them up to 800 °C is investigated by cross sections and the mesurement of hardness in order to prove the suitability for usage in microfabrication.
The formation of gold nanoelectrode arrays was investigated by electrodeposition of the metal along the pores left on directionally solidified NiAl-Re eutectics by selective dissolution of the rhenium fibre. After the necessary pre-treatment for the passivation of the NiAl matrix and dissolution of the rhenium fibres to create arrays of nanopores (diameter ~ 400 nm), the electrodeposition of gold into the pores was initially investigated by examining the growth of the deposits with the application of cathodic pulses. It was observed that the size of the gold deposits increased with the duration of the applied cathodic pulse once an initial charge of ~ 800 C/m2 was overcome. The necessity of applying charges larger than that to observe significant deposits is due to the occurrence of a series of processes alongside the electrodeposition: charging of the oxides present on the eutectic and reduction of any remaining rhenium oxide on the rhenium fibres. Electrodeposition under potentiostatic conditions yielded a better control over the obtained gold structures, and enabled the selective filling of the pores. However, the recorded current transients under those experimental conditions did not obey any of the proposed models for nucleation and growth accurately. This was explained by the simultaneous formation of rhenium oxides and the interference of this process on the recorded current. Nevertheless, the studies reported give initial information on the electrochemical processes that take place when complex metallic substrates are employed for electrodeposition.