Pulse plating of nickel-based alloys

Fig. 1: Cathodic polarisation curves for (a) Ni-Co, (b) Sn-Ni and (c) Ni-W electrolyte systems recorded at a scan rate of 10mVs-1 on a rotating disk electrode at different electrode rotating velocity: 0, 100, 600 and 1000rpm

In the present work, nickel-based alloy coatings (Ni-Co, Sn-Ni and Ni-W) with different microstructures were produced under direct and pulse current conditions. These alloys are of interest as potential replacement for chromium based coatings, especially hard chromium. A replacement for hard chromium coating faces the challenge of providing sufficient hardness values.  For some sliding wear applications, hardness might not be required at the same level as hard chromium, and coating toughness might be more critical.
The effects of the pulse parameters (pulse waveform, pulse frequency and average current density) on the deposit structure and properties of these three systems have been investigated. Pulses have been defined based on the results of electrochemical measurements and numerical process simulation. The surface morphology, microstructure and microhardness of the deposit have been correlated to the pulse parameters applied.
The experimental results showed that applying pulse plating substantially altered the properties of the coatings. The resulting layers exhibited a nano-crystalline microstructure, improved layer compactness and hardness of the nickel-based alloy deposits.


Electrochemical Deposition and Microstructure Characterization of Lead-Tin-Layers

Fig. 3

The present study investigated the formation of a binary alloy of lead and tin. Both elements represent a thermodynamic system with strongly limited miscibility in solid state. The deposition of the layers was carried out under potentiostatic conditions at various deposition potentials from a sulfonate-based electrolyte. The layer formation was characterized by electrochemical techniques (cyclovoltammetry, chronoamperometry). The microstructure development was investigated by SEM/EDX measurements and X-ray diffraction. The layer formation is compliant with the Stranski-Krastanov growth mode. The current efficiency of the deposition was approximately 100%. According to the thermodynamic theory the layers show a dual-phase microstructure. The composition of the Pb-Sn layers was depending on the deposition potential. Supersaturated α-Pb-solid solution could not be observed. The morphology is also strongly depending on the deposition potential. The diffusion coefficient of the metal ions in the sulfonat-based electrolyte was measured by rotating disc electrode experiments. The formal diffusion coefficient in the electrolyte containing Pb2+– and Sn2+– ions is close to the diffusion coefficient of lead ions.


Anodic Film Formation in Oxalic Acid on AlMn0.5Mg0.5 Alloy

The microstructure of oxalic-acid-anodized layers on AlMn0.5Mg0.5 alloy is compared to such layers on aluminum. Differences originate from four types of precipitates occurring in the alloy, forming inclusions in the layers, roughening surface and interface, and modifying typical pore structures of anodized aluminum oxides. A characteristic feature of this modification is the appearance of transverse channels in pore walls. Nanoscaled precipitates are suggested as their origin. Correlation to functional properties such as microhardness and electrical isolation behavior is discussed.


Properties of Gold Composites with Nanostructured Carbon-based Materials

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.