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The corrosion behaviour of microporous nickel-chromium systems was studied by means of conventional electrochemical techniques and localized ones using two chloride based electrolytes with and without cupric ions in their composition. The conscious combination of different methodologies using these techniques has provided valuable information about the corrosion process. Open Circuit Potential (OCP) and Electrochemical Impedance Spectroscopy (EIS) measurements were performed in bulk solution, whilst Scanning Kelvin Probe (SKP) measurement were carried out using two methodologies: i) electrolyte droplets monitoring (measuring simultaneously potential and droplet height with time), and ii) potential maps of dried surfaces that previously were exposed to droplets. Further characterization was done based on the morphology of the attack and composition on the surface by Optical Microscopy (OM), Field Emission- Scanning Electron Microscope (FE-SEM) and X-ray Photoelectron Spectroscopy (XPS) together with the analysis of electrolyte composition with time by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). Results have shown the harmful effect of Cu2+ cations in the corrosion resistance and a different morphological impact on the surface. Such negative effect has revealed a new time constant at high frequency in the impedance diagrams as well as an abrupt potential decrease (due to a change in the cathodic reaction involved: Cu2+ + e− ↔ Cu+ takes place) using SKP droplet test. Apparently, Cu+ species were stabilized in bulk solution by the formation of chloride complexes, as was confirmed by the precipitation of a white CuCl compound during droplet evaporation, pointing out the key role of Cu+ in the corrosion process.

The effect of Cu2+ ions in the corrosion behaviour of microporous nickel-chromium multilayer coatings was investigated by means of electrochemical measurements such as open circuit potential and potentiodynamic polarisation. Data was obtained under exposure to acidified chloride-based electrolytes, varying the content (presence or absence) of cupric ions and the aeration conditions. A field emission scanning electronic microscope was used to obtain micrographs of the cross-section after exposure to different electrolytes whilst an optical microscope was used to characterise the surface appearance. Results have shown that Cu2+ cations are governing the reduction reaction independently of the presence of oxygen according to the polarisation curves. Samples exposed under this electrolyte have shown that the corrosion front was only located into the bright nickel layer. In contrast, the corrosion mechanism was modified in absence of Cu2+ ions. In fact, not only the bright nickel layer was corroded but also the microporous nickel one. It implies a different aesthetic impact on the surface depending on the type of active sites formed in each electrolyte.

The corrosion mechanism of microporous nickel-chromium multilayer coatings was studied at localised scale by Scanning Electrochemical Microscopy (SECM) after exposure to an aggressive electrolyte (chloride-based one at pH 3.1 containing cupric ions). The open circuit potential was initially monitored during 22 h, followed by a detailed characterisation using Glow Discharge-Optical Emission Spectroscopy and Field Emission Scanning Electron Microscope. Interestingly, Cu deposition occurs over the surface of the microporous nickel layer, and it is located on spots where micro-discontinuities (i.e., cracks and pores) of the outermost Cr layer are present. The application of different operation modes of the SECM (i.e., redox competition and surface generation/tip collection) not only reveals such copper deposits (which were identified after monitoring their catalytic capabilities for oxygen reduction reaction) but also confirms the stepwise reduction of Cu2+ to Cu0 (via intermediate species of Cu+) during the corrosion process. The impact of metallic copper particles in the local pH due to their catalytic activity could also explain why the microporous nickel layer is not corroded after exposure to such electrolyte.

A model trivalent chromium-based electroplating bath doped with different concentrations of Fe was used to obtain different metallic coatings. The impact of the Fe was investigated on both the Cr layer and its native passive film by a detailed characterisation using X-ray Photoelectron Spectroscopy (XPS), Angle Resolved XPS and Auger Electron Spectroscopy. Moreover, the semiconducting properties of their oxide layers were explored by Mott-Schottky and the corrosion performance of the coating by linear polarisation resistance and kinetics of the oxide formation. Results revealed not only a homogeneous Fe distribution in the Cr layer but also the presence of an iron-chromium duplex oxide layer for concentrations ≥ 100 mg l−1 Fe in the bath. The Mott-Schottky analysis showed a p-n junction for such coatings due to the presence of an iron oxide layer on top of a chromium oxide one, which increased the total amount of point defects (charge carrier density) and drastically affected to their corrosion resistance (the polarisation resistance decreased by one order of magnitude and their oxide layer showed slower kinetics and a higher passivation current). In contrast, coatings with a single chromium oxide layer showed a p-type semiconducting behaviour as well as the best corrosion performance.

The effects of externally applied uniaxial stress on the magnetic properties of Co thin films and pseudo-spin-valve (PSV) structures on flexible polyimide substrates were investigated. The advantage of the polyimide substrate is its flexibility and high elasticity (∼1%), which cannot be achieved using conventional crystalline substrates. The Co layers exhibit a macroscopic easy axis induced by the preparation process. When the stress is applied perpendicular to the induced in-plane easy axis, the magnetic domains in the film rotate towards the applied stress direction, which was confirmed using Kerr microscopy and magneto-optical Kerr effect (MOKE) magnetometer measurements. A Co/Cu/Ni PSV system was prepared on polyimide substrate with dc magnetron sputtering. Applying uniaxial stress leads to opposite rotation of the magnetisation directions in both layers to each other due to different signs of the magnetostriction coefficients of Co and Ni. The magnetisation and giant magnetoresistance (GMR) curves under applied stress were recorded using in situ MOKE and current in-plane four-point probe techniques, respectively. When the stress is applied perpendicular to the external magnetic field (H ext ), the operating range of the GMR sensor increases, whereas the sensitivity decreases. Anisotropy energies and saturation magnetostriction values of the Co and Ni layer were determined by fitting the GMR and magnetisation curves using a micromagnetic model.