Ionic liquids have generated a large amount of interest as possible replacements for aqueous electrolytes in metal and alloy electrodeposition processes. A related class of fluid, the deep eutectic solvents, have recently been shown to have equally interesting electrochemical properties whilst also being more air and moisture stable and economical to produce. The electrodeposition of Zn from the deep eutectic solvents 1: 2 ChCl: ethylene glycol and 1: 2 ChCl: urea was investigated. A theory of relative chloride activities was developed and applied to effectively account for differences in the voltammetry, chronoamperometry and morphology of deposits obtained from the two solvents. Additionally the solute concentration was determined to have an effect on the physical properties of the solvent; moreover, this effect was seen to be solvent dependent. The first EXAFS study of metal speciation in deep eutectic solvents was used to elucidate the identity of the dissolved Zn species. A novel technique, the combined in-situ AFM-EQCM, has been designed and applied, in a time resolved manner, to the study of Zn electrodeposition from 1: 2 ChCl: ethylene glycol. It was shown that the organic additives ethylene diamine and ammonia could be used to modify the Zn deposit morphology. It has been proposed that the additives alter the Zn nucleation and growth mechanism through interaction with the free chloride ions in the electrochemical double layer. The effect of surfactants has also been described and sodium dodecyl sulphate found to be an effective levelling agent. The feasibility of Zn alloy deposition from choline chloride based deep eutectic solvents has been investigated. Zn-Cu and Zn-Co alloys were successfully deposited from deep eutectic solvents for the first time. In addition the electrochemical quartz crystal microbalance has been used in an original manner to monitor Zn-Sn co-deposit composition.

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This thesis develops the understanding of microstructure formation in binary Sn-Ni alloys during solidification and during soldering. Where past research has found metastable NixSny phases after solid-state ageing of Ni-Sn couples, it has been shown for the first time in this work that metastable NiSn4 forms in the Sn-Ni system during (i) solidification of Sn-rich Sn-Ni alloys as both a primary and a eutectic phase, (ii) soldering of Sn-Ni alloys to Ni-containing substrates as the βSn-NiSn4 eutectic and (iii) during storage of Sn-Ni electroplated couples as the interfacial intermetallic layer. It has been shown that NiSn4 is an orthorhombic phase with a superstructure closely related to oC20-NiSn4 and that NiSn4 is a metastable compound at all temperatures relevant to soldering. Furthermore, it has been shown that a second metastable phase, Ni3Sn7, forms occasionally during solidification. The research has concluded on the following reasons for NiSn4 formation: (i) NiSn4 has growth advantages over equilibrium Ni3Sn4 due to easier interface attachment kinetics; (ii) the existence of a low planar lattice disregistry (~5%) between NiSn4 and Sn results in highly reproducible low energy NiSn4/Sn orientation relationships; and (iii) Fe impurity levels typical for commercial purity solders result in FeSn2 crystals that act as heterogeneous nucleation sites for NiSn4. Investigation of Sn-Ni electroplated couples showed that the interfacial layer is metastable NiSn4 initially and that Ni3Sn4 nucleates and grows to consume the NiSn4 layer with time at temperature. A similar study on Sn-Ni solder joints showed that the interfacial layer is always Ni3Sn4. The results suggest that, in electroplated couples, metastable NiSn4 nucleates on βSn due to the low planar disregistry between the phases. In contrast, during soldering the interfacial intermetallic nucleates on the Ni substrate when the solder is liquid and the metastable NiSn4 has no nucleation advantages over equilibrium Ni3Sn4.

Little work has been dedicated to the magnitudes of the strain paths that are imposed on a workpiece during various industrial thermomechanical processing (TMP) routes. Furthermore, previous strain path work has concentrated on linear, sequential and full reversal strain paths due to the ease of performing such tests. No work has been carried out on the complex concurrent strain paths which are imposed during TMP. By combining finite element (FE) modelling and the new Arbitrary Strain Path (ASPII - the second generation of its kind at the University of Sheffield) machine such work is now possible. The ASPII machine is a test rig capable of imposing independent or concurrent torsion and axial components of deformation under fixed or free end conditions. The machine in equipped with an induction heater capable of testing materials up to 1100ne and a water quenching system to capture high temperature deformation microstructures. An induction coil heating system also allows controlled slow air cooling to be carried out to closely reproduce industrial cooling rates. The machine has been calibrated to accurately carry out full reversal in the deformation direction (torsion and tension/compression) over the temperature range of 600-11 oooe up to a strain rate of IOs' I with negligible delay or overshoot. Model parameter sensitivity analysis, material flow behaviour and model validation have been carried out using axisymmetric FE models for a range of temperatures (950, 990, 1030°C) and strain rates (0.2, 2, 20s·l ) combined with actual tests carried out within IMMPETUS. The simulations demonstrated that over the tested temperature. strain and strain rate ranges, the models were largely unaffected by most thermal input parameters (e.g. thermal conduction.), The mesh density and friction coefficient have been shown to have the largest influence on FE model output. FE simulation of a two stage closed die forging of an arbitrary aero engine compressor disc has been carried out. This model has provided 'typical' process parameters to carry out extreme strain path change tests i.e. full reversal tests. Such tests were undertaken to evaluate any effects on the similarly orientated primary alpha grain clusters that are responsible for reductions in fatigue life under dwell loading situations. Such extremes changes in strain path were unsuccessful in breaking up the clusters. By tracking nodes within the FE model the deformation history has been extracted and subsequent strain paths have been calculated for three points of interest within the forged material. This information has been transferred to the ASPII machine and the deformation has successfully been replayed. Initial tests were followed by a simulated industrial slow air cool. Later work quenched the samples after the forging strain path simulation. It was seen that different strain paths do influence the morphology of the microstructure however in terms of micro and macro texture no significant difference can be found.

The objective of the investigation was to establish melting relationships in certain phase diagrams of importance to the technology of basic refractories, with special reference to the effects of the solid solubility of Al203, Cr203 and iron oxide in magnesia at high temperatures. Because of this solubility, the freezing paths of mixtures lying in the primary phase volumes of periclase in the systems caO-MgO-Al203-Si02, CaOMgO- Fe203-Si02 and CaO-MgO-Cr203-Si02 do not radiate from the MgO corner of the composition tetrahedron. Bence projections of the boundary surface of the primary phase volume of periclase, through the MgO corner onto the opposite face of the tetrahedron, do not describe the freezing behaviour of such mixtures accurately. The first investigation was of the phase changes occurring in mixtures containing 80 Wt.% MgO in the system CaO-MgO-Al203-Si02. conventional techniques involving firing and microscopic examination, after water quenching were used to establish the identity and crystallization temperatures of the secondary phases and the results were plotted on a composition triangle in terms of the cao, A1203 and Si02 contents of the mixtures recalculated to 100 wt.%. comparison of this diagram with the published diagram of the boundary surface shows that displacement of the boundary lines due to solid solution of AlaO, becomes appreciable at temperatures over lSOOoC, where the solid solubility of this oxide becomes appreciable. COmparison with similar diagrams established in the Department for the systems CaO-MgO-FeaO,-SiOa and CaO-MgO-cra03-SiOa has further shown that, at comparable MgO contents the range of Ra03/(CaO + SiOa) ratios over which spinel is the secondary phase decreases in the order AlaO, > Cra03 » FeaO, which is the order of increasing solid solubility of the sesquioxide in periclase at high temperatures. An explanation for this effect has been advanced and a graphical method of predicting the displacement of the spinel-silicate boundary with varying MgO content has been described.

Magnesium alloys are very promising materials for automotive and aerospace applications due to their low density. The market of medical implants (e.g. temporary orthopaedic and cardiovascular implants) is another field of possible applications of magnesium alloys since they can completely dissolve within human body without causing any major health issues. Unfortunately, magnesium alloys have been well-known from their low formability at room temperature and poor corrosion resistance. The aim of the current work was to improve mechanical properties of a magnesium alloy by incremental equal channel angular pressing (I-ECAP). The goal of the process is to refine grain structure of a continuous bulk metallic billet without changing its dimensions. In the current work, the most popular wrought magnesium alloy AZ31B was subjected to I-ECAP for the first time to confirm potential of the method for industrial production of innovative lightweight materials. The process window was determined on the basis of I-ECAP experiments conducted with various process parameters (temperature, processing route, initial grain size of the alloy). Additionally, various microstructural characterization methods, including ex situ and in situ analyses, were incorporated in this work to show a relation between the grain size and the deformation mechanisms occurring in the alloy. It was found that mechanical properties of AZ31B can be tailored to a specific application by using different process parameters. It was shown that yield strength can be increased from 165 MPa to 290 MPa when temperature of I-ECAP is reduced to 150°C. Moreover, room temperature ductility of the produced material can exceed 40% when a combination of I-ECAP and subsequent heat treatment is applied. The results of the work confirmed that I-ECAP could be considered as the useful method for producing advanced lightweight metallic materials with a potential for industrial applications.

Impact resistant materials (IRMs) are widely used in the automotive and packaging industry. Their main purpose is the protection of the transported occupants or goods. Cellular materials as well as structures combine lightness with large deformation under load. The energy absorption mechanism is provided by limiting the peak load and ensuring the elastic deformation of the IRMs. Polymeric foams are largely used as IRMs due to their cellular structure. Prediction of the foam properties in terms of Young’s Modulus (Elastic Modulus) and the onset of Plateau Region can be related to the foam density and the mechanical properties of the bulk material (Gibson and Ashby model). The structure of the foam is only partly accounted for in the Gibson and Ashby model in terms of material density. However, it is possible to produce cellular materials with the same density but very different internal architectures. This cannot easily be exploited in conventional polymer foams but the processing of High Internal Phase Emulsion (PolyHIPE) and its polymerisation route to produce PolyHIPE Polymers (PHPs) can produce materials with very different structures. Experiments have revealed that the PHPs properties are dictated by their detailed structure. Elastic PHPs with: 1) varying ratio of polymerizable oil phase with respect to aqueous phase and 2) varying mixing time/energy input were produced and tested by mechanical compression at different temperatures and strain rates. The elastic modulus increases with a quadratic law as a function of the polymerizable oil phase content of the HIPE when the mixing time is the same, as predicted by the model. The Specific Absorption Energy (SAE), represented by the area under the stress-strain curve, increases in a similar way. Increasing mixing time on HIPE has the effect of modifying the cellular structure. Smaller pores and narrower distribution of pores are observed. Such features are consistent for any set of PHPs densities and represent a design tool when some specific mechanical characteristics are prescribed. The assessment of process-structure-properties relationships was performed by combining the mechanical response of the various PHPs with the imaging of their structure by Scanning Electron Microscopy. The properties of PHPs were benchmarked with reference to two commercially available products. One material is characterised by a porous structure with a relatively high Young’s Modulus while the other by a non-porous and composite-like solid structure with lower elastic modulus. The properties of the PHPs can be engineered to shift from a foam-like material to a composite-like through the processing parameters which in turn modify the material porous structure. The temperature has very limited effect on the PHPs material unlike for the reference commercial materials. The enhancement of properties (increasing Elastic Modulus and SAE) induced by changing the processing route are remarkable for such a class of porous materials. When plotted on a Modulus-Density chart, the PHPs fill an existing material-chart gap, representing a new class of materials and opening new possibilities as IRMs.

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