The grain growth behaviour during reheating between 950 ºC and 1300 ºC of as-cast Al-Nb steel (containing 0.019 wt% Nb and 0.057 wt% Al) and rolled Nb-containing steel (containing 0.028 wt% Nb and 0.031 wt% Al) have been investigated. In particular the role of microalloying element segregation during casting and, hence the spatial distribution of microalloying precipitates, on grain boundary pinning during reheating has been considered. The Al-Nb containing steel has been examined in separate initial conditions, including as-cast (segregated structure), homogenised and forged (reduced separation of segregated bands) samples. It was found that microalloy segregation occurred between the dendritic and interdendritic regions, where the secondary dendrite arm spacing (SDAS) was 150 ± 50 μm. Nb showed strong segregation into the interdendritic regions resulting in a higher number density of Nb(C,N) precipitates (2.64 × 104 /mm2) compared to the dendritic region (0.73 × 104 /mm2). However, Al did not show strong segregation resulting in relatively well-distributed AlN precipitates in the matrix (1.29× 104 /mm2 in the interdendritic region and 1.89× 104 /mm2 in the dendritic region). After forging, the separation between the segregated bands was reduced to 65 ± 10 μm from the previous 150 ± 50 μm in the as-cast sample. The increased Nb content in the rolled Nb-containing steel compared to the Al-Nb steel gave a greater extent of segregation in the solute-enriched regions resulting in a larger number density of Nb(C,N) present (5.9× 104 /mm2), whilst the separation between in the segregated bands in the as-rolled Nb-containing steel was 35 ± 10 μm.

Electronic structure calculation methods, coupled with unbiased global optimization schemes are developed and employed, for the exploration of the energy landscape of subnanometre scale metallic clusters of noble metals. Structure prediction, along with statistical analysis of the potential energy surfaces for ultrasmall metallic and bimetallic particles of the coinage metals (Cu, Ag, Au) and platinum group metals (Pd, Pt) is undertaken, to determine favourable cluster geometries. Prediction of energetic and electronic properties, including charge distributions, electronic and configurational densities of states, binding, adsorption and mixing energies are made, in order to support the predictions of novel experimental work on a potential catalytic and optoelectronic systems. The environment of the particle is a focus, with surface-bound, ligated and gas phase clusters all considered, in addition to modelling of the adsorption of small molecules. Subnanoscale metal systems show promise in a range of reactive and electronic roles, and by producing accurate theoretical predictions of optical, binding and electronic properties, we contribute to the rational design of such new materials.

Shot peened steel tubing made from 304HCu-grade austenitic stainless steel was exposed to temperatures of 600-750°C in three atmospheres: vacuum, deoxygenated atmospheric pressure steam and deoxygenated 70bar steam. The microstructural changes and oxide morphologies of the shot peened material were observed with SEM, TEM, microhardness testing and TKD mapping. An estimate of the lifetime of the shot peened microstructure in service conditions was made based on service temperature. MnCr2O4 spinel was observed on oxidized samples and the consequences of this are discussed.

Focus of this thesis are the magnetic shielding aspects of a mobile atom interferometer, developed under the Gravity Gradient Technologies and Opportunities Programme (GGtop). This system has been used as a test bed for new compact technologies with the aim to perform outdoor gravity gradient measurements. A finite element analysis model was used for optimising magnetic shielding design, aiming to reach a field attenuation factor of the order of 103, by mu-metal. The research was extended to alternative shielding techniques with the intention to push current technology towards next generation portable atomic sensors. Initially, Metglas foil was used to create lightweight cylindrical shielding housings. The performance goal was approached by a total of 37 foil wrappings around two coaxial cylinders. However, material inhomogeneities affected the magnetic field uniformity. The second approach exploits additive manufacturing of permalloy-80 for 3D-printing compact shielding structures. Process optimisation was undertaken by fabricating approximately 70 small bulk samples under different printing parameters, while 6 cylindrical shield prototypes were produced for preliminary shielding tests. Application of post heat treatments enhanced shielding effectiveness by a factor of up to ~ 15, indicating that a performance closer to mu-metal could potentially be reached by further process optimisation.

The oxidation behaviour of RR1000 with different surface modifications has been well studied using detailed metallographic and mass gain measurements. The oxide comprises of an external chromia scale with isolated grains of TiO\(_2\) on the outer surface. Sub-surface internal alumina is present, beneath which the presence of TiN occurs (at higher temperatures >800\(^o\)C), all contained within a ɣ' denuded zone. The chromia external scale growth rate is significantly greater than pure chromia on chromium and the enhancement is attributed to the increased ionic transport caused by doping of the chromia layer with Ti. This effect is still seen regardless of surface condition prior to oxidation. Oxides, especially internal intergranular oxides have been shown to crack under room temperature fatigue conditions, causing a significant fatigue life deficit at a maximum applied stress of 800 MPa and 1000 MPa. At 825 MPa, it is suggested that plastic yielding of the ɣ' denuded zone initiated leading to a substantial increase in fatigue life, through either blunting the crack by deforming to accommodate the stress concentration at the crack tip or by preventing cracking of the oxides.

Topology, a mathematical concept associated with global perspectives, was found to represent geometric aspects of physics. To date, various topological phases have been proposed and classified. Among them, topological gapless phases focusing on the degeneracies of energy bands serving as the singularities in the momentum space, attract much attention. Especially in the three-dimension, various topological semimetals have been proposed. With unit topological charge ±1, Weyl degeneracies have laid the foundation. Also, they show loads of exotic properties, such as Fermi arcs and chiral anomalies. Being relied on the band topology theory, topological gapless phases have also been transferred into classic systems, such as photonics, acoustics and mechanics. Here, we experimentally investigated photonic Weyl systems in the photonic continuum media, where electromagnetic intrinsic degrees of freedom play key roles in constructing the state space. Firstly, we researched chiral hyperbolic metamaterials, a type-II Weyl metamaterials, from which we directly observed topological surface-state arcs. Then, we report the discovery of ideal photonic Weyl systems, where helicoid structure of nontrivial surface states has been demonstrated. Finally, we construct photonic Dirac points, through analysing eigen reflection field, we found the correlation of topological charges in momentum and real spaces.

In this project a novel combinatorial synthesis method, Suspended Droplet Alloying (SDA), has been developed for the rapid production of small, bulk alloy samples for the large EU FP7 collaborative project, Accelerated Metallurgy. SDA can produce a discrete mm-sized fully dense alloy button with precise stoichiometry in several minutes. Samples of many different alloy systems have been produced by SDA but this thesis will only present work on the Ti-Al-V, Ti-Al-Fe and Ti-Al-Nb alloy systems. Ti-Al-Nb alloy samples are difficult to make due to the high melting point of Nb, so the SDA process parameters have been optimized in order to make homogeneous Ti-Al-Nb alloys. The fundamentals of the SDA process have been studied in terms of the formation of the droplets and the consistency of the process. Splats deposited by the impact of individual alloy droplets have also been investigated. Finally, SDA has been used to explore the influence of a fourth elemental addition to a Ti-46Al-8Nb alloy. The elements added are V, Hf, Cr and Zr. It has been found that the addition of V can increase the ductility of Ti-46Al-8Nb alloy significantly.

Atmospheric pitting corrosion of austenitic stainless steels 304L and 316L under droplets of MgCl2 have been studied under conditions of relevance to long-term storage of nuclear waste containers using automated deposition of arrays of droplets. The effect of microstructure on the morphology of atmospheric corrosion pits in 304L stainless steel plate was investigated. The presence of retained delta ferrite was found to influence the morphology of pits. Ferrite bands were preferentially attacked, and pits were found to have layered attack morphology dependent on the rolling direction and plane of the metal surface. Solution annealing of stainless steel resulted in ferrite reduction and formation of faceted pits. Pits can grow with an initial shallow dish, which may propagate via ‘earring’ or small satellite pits. The size and morphology were seen to vary with exposure humidity, chloride deposition density and distance from the droplet edge. Pits propagated readily above chloride densities of ~10-4 µg/cm2, depending on alloy and exposure time. Below this value much smaller pits were observed due to a discontinuous solution layer. The formation of secondary spreading and micro-droplet formation was observed for MgCl2 droplets on stainless steel when pits form close to or at the droplet edge. Small pits developed beneath these micro-droplets at lower humidities. This work provides a basis to make recommendations for long-term storage conditions of intermediate nuclear waste (ILW) in order to minimise the risk of pitting corrosion.

The present investigation, which forms part of a general programme of research into the effects of departures from the stoichiometric composition on the physical and mechanical properties of ceramic compounds, is concerned with the defect structure of non-stoichiometric rutile. The physical properties of rutile, with particular reference to the effects of departure from the stoichiometric composition, have been briefly reviewed. The development and design of an apparatus, incorporating a sensitive microbalance, capable of measuring departures from the stoichiometric composition in rutile at low pressures of oxygen and at temperatures up to a maximum of 1300\(^o\)C is described in detail. The defect structure of non-stoichiometric rutile has been shown to alter as departure from the ideal composition increases. It is concluded that at small departures from the stoichiometric composition free anion vacancies are present, whereas at large departures the vacancies cluster on planes of the {100}, {101} and {110} types, which subsequently collapse by displacement of ½<101> forming interstitial cations. The departures from stoichiometric composition which have been observed in high-purity rutile are very small - much smaller than those previously reported in the literature. Larger departures found to occur in impure rutile can be attributed directly to electronic effects associated with impurity atoms. Much further work of a systematic and long-term nature will have to be carried out before the role of impurity atoms on the defect structure of non-stoichiometric rutile is understood.

As-cast Mg\(_9\)\(_4\)Zn\(_2\)Y\(_4\) alloy has been subjected to compression and equal channel angular pressing (ECAP) separately. The as-cast alloy contains mainly a long-period stacking ordered (LPSO) phase and a Mg\(_2\)\(_4\)Y\(_5\) phase as secondary phases. During compression, kinking occurs in the LPSO phase and LPSO/Mg mixture. Most kink boundaries of LPSO are composed of basal < a > type dislocations. The rotation axes of the kink boundaries in LPSO/Mg are preferentially located in the (0001) plane. ECAP processing develops a bimodal microstructure consisting of large deformed grains and sub-micron dynamically recrystallised (DRXed) grains. The DRXed grains are mainly located along the original grain boundaries. Kink boundaries also acts as DRX nucleation sites. The ECAP processing increased significantly the strength of the alloy. In the as-cast Mg-Zn-Y alloys, the main secondary phase changes when different ratios of Zn/Y are applied: LPSO (Zn/Y ratio is 0.5) → LPSO+W (Zn/Y ratio is 1, W is Mg\(_3\)Zn\(_3\)Y\(_2\)) → W (Zn/Y ratio is 2.33). When Y is half replaced by Gd, the types of phases are similar. When Y is replaced fully by Gd, W phase becomes the main secondary phase. The structure of the LPSO also changes with different Zn/Y ratios and the presence of Y or Gd.