A fundamental study of electropolishing of stainless steel and nickel based single crystal superalloy CMSX-4 in type III deep eutectic solvent based on choline chloride and hydrogen bond donor i.e. mixture of choline chloride with ethylene glycol in a 1:2 molar ratio was carried out and had been found to be competitive with the current concentrated mixture of inorganic acid electrolytes. Life cycle study was conducted to define the key process controlling factors like electrochemical stability, current efficiency, effect of history of electrolyte, recycling of ionic liquid and its reuse for electropolsihing. The electrochemical techniques like linear sweep anodizing curves, chronoamperometery and galvanostatic studies revealed that electropolishing in 1:2 ChCl:EG proceeded through the formation of viscous layer on the surface of the substrate similar to electropolishing in inorganic acid electrolytes. The optimization of electropolishing process was carried out using the experimental design strategies, Fractional Factorial Design (FFD) and found that electropolishing variables like addition of water, oxalic acid, electropolishing bath temperature, time and potential had positive impact on the surface finish. Surface texture measurements such as surface roughness and surface overlayer morphology of electropolished stainless steel and CMSX-4 was carried out using the microscopic techniques, atomic force microscopy (AFM), scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM) and digital holographic microscopy (DHM) and found to be the function of electropolishing time. Effect of electropolishing on corrosion behaviour of stainless steel was studied using the electrochemical techniques like open circuit potential measurements (OCP), potentiodynamic polarization curves and gravimeteric method showed improvement in the general or pitting corrosion of the workpiece. Nickel based superalloy was also successfully electropolished to remove the casting scales. The dissolution of two phases was found to be the function of electrochemical regime i.e. applied potential and current density.

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The electrodeposition of tin/chromium and tin/zinc/chromium is a new field of research. This field was investigated because it may be of commercial, as well as scientific, interest if a range of alloy compositions could be sustainably deposited from environmentally acceptable electrolytes. With no published work to guide this research difficulties were encountered in producing sustainable deposition procedures. A novel electrolyte that deposited tin/chromium alloys in a range of compositions was produced. This electrolyte was adjusted to produce novel tin/zinc/chromium deposits in a range of compositions. However the thickness of deposited tin/zinc/chromium was limited to 300nm. It was hypothesised that polymerised chromium glycine could be used as a weak brightener to increase deposit thickness. This produced another novel electrolyte and it was confirmed that chromium could be codeposited from polymerised chromium glycine with tin and zinc. This electrolyte produced deposits in a range of compositions and produced tin/zinc/chromium deposits up to 3Jlm thick. The ability to deposit chromium from the polymerised electrolyte was enhanced by the codeposition oftin. This induced codeposition of chromium with tin had not previously been reported. It was observed that tin metal was dissolved by the chromium glycine electrolyte and that this dissolved tin was not precipitated out. It was suggested that the dissolved tin could be electrodeposited with chromium. Experimentation confirmed this hypothesis. The alloy produced was rich in chromium, 6Jlm thick and of a bright appearance. Tin/chromium and tin/zinc/chromium deposits were analysed by Mossbauer and X-ray Diffractometry and p-tin identified in all samples examined. Significantly tin only phases could not explain the Mossbauer and X-ray diffraction results, the presence of other tin microenvironments are required. However the lack of standards for comparison made identification of such microenvironments difficult.

The advent of the closed field unbalanced magnetron sputtering (CFUBMS) technique has provided a novel method for the production of ultra thick multilayer coatings, which form free standing foils when removed from the substrate. Applications for this method range from the production of complex metal/ceramic probe tips, to an alternative route for the production of axisymmetric high precision-machined components, such as a bellows component used in the production of uranium enrichment by the sponsors of this project, Urenco (Capenhurst) Ltd. In this study the CFUBMS system was developed to grow metallic and reactive compound multilayer foils. These foils were tested for compatibility with uranium hexafluoride, UF6 , a corrosive gas used in the production of enriched uranium that is also in contact with the bellows component.

The electroplating industries use soluble nickel salts in numerous applications. Over the past few years this has become problematic due to the reclassification of these salts from a harmful substance to now a toxic substance. The introduction of the legislation REACH (Registration, Evaluation, Authorisation & restriction of CHemicals) has meant the electroplating industry has had to use less harmful chemicals where possible, thus meaning companies are investing in research to find an alternative to the nickel deposit. In this study, alternative deposits under investigation as a potential replacement to the nickel deposit under the decorative chromium deposit has been characterised in terms of the appearance, surface topography and corrosion resistance by using spectrophotometry, scanning electron microscopy (SEM), atomic force microscopy (AFM), linear polarisation, electrochemical impedance spectroscopy (EIS) and accelerated corrosion salt spray methods. Spectrophotometry identified that a white Cu-Sn alloy gave a bluer appearance in comparison to the nickel deposit, when the chromium deposit was plated on top this modified the colour slightly giving the white Cu-Sn alloy with chromium a similar appearance to the nickel and chromium deposit. The yellow Cu-Sn alloy was yellow in colour with a visibly dull appearance, but when chromium was plated on top of the yellow Cu-Sn alloy the colour was improved but still remained dull. The SEM and AFM results identified that the white Cu-Sn alloy deposit had similar nodulated topography to the nickel deposit and when the chromium was plated on top the topography changed only slightly. While the yellow Cu-Sn alloy deposits showed a more crystalline structure and increased roughness in comparison to the nickel deposit, the chromium deposit plated on top did not change the structure of the underlying deposit but it did reduce the roughness slightly. Electrochemical corrosion tests showed the white Cu-Sn alloy to have a higher polarisation resistance compared to the nickel deposit, thus suggesting it would provide similar corrosion protection to the nickel deposit. The yellow Cu-Sn alloy proved to have a faster corrosion rate in comparison to the nickel deposit. Accelerated corrosion tests proved the white Cu-Sn alloy to be more corrosive than the nickel despite the electrochemical test results, it was concluded that the white Cu-Sn alloy deposit was porous and therefore provided less corrosion protection to the substrate in comparison to the nickel deposit. The yellow Cu-Sn alloy had a lower corrosion protection than the nickel deposit and when combined as a duplex Cu-Sn alloy with the white Cu-Sn alloy deposit there was no improvement in corrosion performance. The plated chromium deposit did improve the corrosion protection for most deposits but none of the alternatives could match the corrosion protection offered by the standard nickel with chromium deposit. This study concluded that the white Cu-Sn alloy with chromium deposit was found to be a potential alternative to the nickel with chromium deposit for applications where appearance is primary, no alternative could be found to match the corrosion protection provided by the standard nickel and chromium process.

The aim of this research proj ect was to produce compositionally modulated zincnickel and zinc-nickel-manganese coatings usi ng a single bath process by variation of the applied electroplating current density. These could then be considered as possible replacements for electroplated cadmium. Zinc-nickel electrodeposits from both a simple bath and one containing the complexant tris(hydroxymethyl)methylamine (TRIS) were produced using either bath or by selective electroplating onto mild steel, 2014-T6 aluminium and 2000 series aluminium alloy connector shells. Zinc-nickelmanganese coatings were electroplated onto mild steel, using both DC and pulse electroplating from sulphate based baths containing either the complexant TRIS or sodium citrate. The coatings and the various electrodeposition processes were evaluated by thickness measurements, cun'ent efficiency calculations, composition detennination using energy dispersive X-ray anal ys is and SEM to examine the morphology. Corrosion characteristics were investigated by neutral salt fog exposure, alternate immersion, atmospheric trials, and electrochemical immersion tests including potential monitoring, galvanic and polarisation measurements. Other properties such as microhardness and surface electrical conductivity were also investigated. Compositionally modulated zinc-nickel and ziJlc-nickel-manganese were successfully deposited from single baths with nickel contents ranging from 5-20% Ni and manganese contents varying from 0-12% Mn. Current efficiency measurements showed the efficiency to be low especially for the zinc-nickel-manganese coatings, which exhibited a distinct morphology when electroplated from the citrate bath. Corrosion testing indicated that both coatings had a lower corrosion resistance than cadmium especially in accelerated tests, with a reduction in corrosion resistance being seen as the nickel content was increased; due to a decrease in density of the electroplate. This, and increasing through-thickness porosity promoted ennoblement of zinc-nickel and zinc-nickel-manganese leading to the coatings becoming nonsacri ficial to the substrate in accelerated tests. Zinc-nickel-manganese showed less white rust than zinc-nickel and exhibited lligher micro-hardness than zinc, cadmium and zinc-nickel. Electrical measurements indicated that both coatings were sufficiently conductive to meet the surface conductivity requirements for use on electrical connector shells.