In recent years rare earth metals have hit the headlines due to supply restrictions of neodymium and dysprosium from the main supplier China. The work in this thesis investigates the possibility of recycling sintered NdFeB-type magnets using a combination of hydrogen decrepitation (HD) and the HDDR process (Hydrogenation Disproportionation Desorption and Recombination). In this work the development of microstructure during the HDDR process has been identified and the route taken by hydrogen during absorption and desorption. The microstructure and magnetic properties have been shown to be affected by the process temperature, disproportionation pressure and recombination pressure and time. Sample batches up to 100g exhibit little variation in magnetic properties however 400g batches result in large variations partially due to incomplete recombination. By increasing the disproportionation pressure it was possible to simultaneously process mixed scrap feeds with different Dy and Co levels, however a large variation in magnetic properties was also observed. Optimal processing of sintered Nd\(_{13.4}\)Dy\(_{0.7}\)Fe\(_{78.6}\)Al\(_{0.7}\)Nb\(_{0.4}\)B\(_{6.3}\) was performed by in-situ HD followed by HDDR at 880\(^o\)C with a disproportionation pressure of 1500mbar and recombination under vacuum. The resultant powder exhibited a remanence of 1.08 T, coercivity of 840 kAm\(^{-1}\) and maximum energy product of 178 kJm\(^{-3}\).

This study involved the characterisation of a newly developed 9%CrMoCoVNbNB (FB2) martensitic creep resistant steel for use in large industrial turbine disc and shaft components. A major part of the work involved characterisation of FB2 with incorporation of material, thermal and physical data into a finite element-based model for the simulation of coupled thermo-mechanical working with consideration of grain size evolution based on the implementation of a user sub-routine within the FEM code (QForm). The main focus of the research was to gain a comprehensive understanding of the non-uniform temperature, strain rate, strain and grain size distributions apparent during hot open-die forging.

High Pressure Die Casting (HPDC) is an attractive option for automotive manufacturers, as it has a number of advantages over wrought process routes. An improved understanding of the defects which may result from the process could allow castings to deliver lighter vehicle structures. A novel algorithm was developed to predict the formation of entrainment defects, which may limit the strength of castings. This model was integrated into FLOW-3D, a fluid dynamics solver. Theoretical advances were made, which offer a means of extrapolating a spatial distribution of damage to location specific statistical distributions, an improved way of characterising the contribution of each defect type to strength, and a means of correlating parameters for statistical distributions, allowing the variation in strength may be predicted at arbitrary locations within a casting. Casting and numerical experiments were performed, to evaluate these algorithms and underlying fluid flow solution, and to test the influence of entrainment defects on the strength of HPDC parts. Defects formed by air entrainment were found to significantly limit the strength of the studied castings. The methods and techniques explored in this work showed promise, but further advances would be needed, before ab intio strength prediction for HPDC parts can be realised.

Hospital acquired infections is a modern day reality which plagues health care system around the world. Infections are the cause of 37,000 deaths and a 20 billion euro expense in EU annually. Despite the attention that such infections receive in scientific literature, very few viable solutions have been put forward and implemented. This study systematically developed, characterised and optimized novel long-lasting antibacterial surface coatings for use in medical devices, surgical instruments and hospital equipment. The reactive magnetron-sputtering deposition technique was successfully employed to combine the high mechanical performance of the nitrogen AISI 316 S-phase coating and the antibacterial efficacy of the elements silver and copper. Various configurations including homogeneous monolayers and layered multilayers were investigated for the first time in literature. It was found that substitutional silver and copper atoms can reside within the S-phase lattice while the good corrosion and wear resistance of S-phase are maintained by carefully controlling deposition parameters. Silver was observed to significantly increase the nitrogen uptake up to a previously unreported level of 50at% which has been termed 'ultra-saturation'. Copper based multilayers were found to have a 100% bacteria elimination rate, while silver monolayers also exhibited a good antibacterial efficacy against Staphylococcus aureus.

NiTi-based shape memory alloys (SMAs) have been developed as high power density micro-actuators for small scale and/or light weight actuation systems; this provides opportunities for actuators to be installed in regions where conventional actuators are unattractive due to their size, weight or power consumption. SMA based actuators could be applied across a greater range of applications if the SMA that provides the force could be joined to other light weight engineering materials, such as Ti-6Al-4V. The scope of this work is to describe the reasons why conventional fusion based welding and brazing procedures fail to provide strong joints between Ti-6Al-4V and NiTi-based SMAs, then detail a novel brazing method that can join these materials. This novel joining method involves using a localised heating method to braze the parent metals together. This localised brazing method prevents the shape memory properties from being compromised. The strength of the joints produced in this work have been related to their microstructure, which in turn have been related to the processing steps used to produce the joint. A study of the processing parameters was conducted to investigate the potential of this method as a large scale production joining method.

The motivation for this work was provided by the results of an interdisciplinary, multi-university research programme funded by the Ministry of Defence. The significant finding in question was that the stress corrosion cracking (SCC) resistance of AISI type 304 stainless steel (SS) alloys can be significantly improved by the addition of the platinum group metals (PGM), ruthenium and palladium. The increased SCC resistance could be attributed to the enhancement of the cathodic hydrogen reduction reaction. Thus, the primary objective of this work was to confirm that the increase in hydrogen production at the surface would not counteract the improvement in SCC resistance by increasing the susceptibility to hydrogen embrittlement (HE). Electrochemical hydrogen charging was employed and melt extraction was used to measure the bulk concentration of absorbed hydrogen as a function of alloy chemistry. Both Ru and Pd doped experimental 304 SSs showed a decrease in the concentration of absorbed hydrogen compared to an experimental standard 304 SS (i.e., a controlled, non PGM-doped reference 304). This result is thought to be due to the PGMs enhancing the recombination kinetics of adsorbed hydrogen. Ru proved more effective than Pd at hindering absorption and this is likely associated to the more homogenous distribution of Ru in solid solution. Slow strain rate tensile (SSRT) testing was performed in air at sub-ambient temperatures on pre-hydrogen charged specimens. PGM addition was found not to increase the susceptibility of 304 to HE. Conversely, an approximately equal enhancement of the HE resistance was observed for the addition of both Ru and Pd. The modest improvements are attributed to the reduced concentration of absorbed hydrogen, with a further possible beneficial trapping effect of Pd concentrated bands, contributing to the HE resistance of Pd doped 304.

The growing demand for ever more greener aero engines has led to ever more challenging designs and higher quality products. An investigation into Coordinate Measuring Machine measurement uncertainty using physical measurements and virtual simulations revealed that there were several factors that can affect the measurement uncertainty of a specific task. Measurement uncertainty can be affected by temperature, form error and measurement strategy as well as Coordinate Measuring Machine specification. Furthermore the sensitivity of circular features size and position varied, when applying different substitute geometry algorithms was demonstrated. The Least Squares Circle algorithm was found to be more stable when compared with the Maximum Inscribed Circle and the Minimum Circumscribed Circle. In all experiments it was found that the standard deviation when applying Least Squares Circle was of smaller magnitude but similar trends when compared with Maximum Inscribed Circle and the Minimum Circumscribed Circle. A Virtual Coordinate Measuring Machine was evaluated by simulating physical measurement scenarios of different artefacts and different features. The results revealed good correlation between physical measurements uncertainty results and the virtual simulations. A novel methodology for the automated assessment of leading edge airfoil profiles was developed by extracting the curvature of airfoil leading edge, and the method lead to a patent where undesirable features such as flats or rapid changes in curvature could be identified and sentenced. A software package named Blade Inspect was developed in conjunction with Aachen (Fraunhoufer) University for the automated assessment and integrated with a shop floor execution system in a pre-production facility. The software used a curvature tolerancing method to sentence the leading edge profiles which aimed at removing the subjectivity associated with the manual vision inspection method. Initial trials in the pre-production facility showed that the software could sentence 200 profiles in 5 minutes successfully. This resulted in a significant improvement over the current manual visual inspection method which required 3 hours to assess the same number of leading edge profiles.

With relatively high gravimetric and volumetric hydrogen storage capacities, borohydride compounds are being investigated for their potential use as hydrogen storage media. A study has been made into the mechanical milling of metal chlorides with sodium borohydride to try to form homoleptic borohydrides. Mechanical milling of zinc chloride with sodium borohydride resulted in the formation of a covalent complex NaZn\(_2\)(BH\(_4\))\(_5\). Thermal decomposition occurred at 80°C with a mass change of 12 wt.%, associated with the evolution of hydrogen and diborane. A composite mixture with magnesium hydride a reaction between diborane and magnesium hydride was observed form magnesium borohydride. Mechanical milling of calcium chloride or magnesium chloride with sodium borohydride did not produce calcium borohydride and magnesium borohydride, but rather resulted in solid solutions where chlorine ions substitute for borohydride ions within the cubic sodium borohydride lattice. Thermal decomposition of milled calcium chloride and sodium borohydride occurs at a similar manner to that of Ca(BH\(_4\))\(_2\) (from Sigma-Aldrich). Milled magnesium chloride and sodium borohydride thermally decomposes via several unknown phases with a weight loss of 4.4 wt.% yielding Mg, MgB\(_2\), B, and [B\(_{12}\)H\(_{12}\)]\(^{2-}\). Lithium borohydride investigated using Raman spectroscopy. After heating lithium borohydride through its orthorhombic to hexagonal phase change (118°C) and melting point (280°C), shifts in Raman peak position and peak width were measured as a function of temperature. This work shows the in-situ decomposition of LiBH\(_4\) observing formation of lithium dodecaborane (Li\(_2\)B\(_{12}\)H\(_{12}\)) at 340°C and amorphous boron from liquid lithium borohydride.

In this thesis, studies associated with the stability analyses of the box-shaped dump-site culvert constructed in Tinaz Surface Mine of Turkish Coal Enterprises (TKi) are presented. In addition, stability conditions of other culvert alternatives are evaluated. Existence of creeks in a surface mining area is a significant factor to be considered in selection of dump-site location. Since, the dumped overburden material on the valley acts as a barrier and behaves like a dam causing flood problem behind the dump-site. TKi engineers prevented the flood potential that might have occurred behind the dump-site by constructing a 480-meter long reinforced-concrete culvert on the downstream of Gevenez Creek Valley. However, considerable amount of deformations occurred in the first 100 meters of the culvert, as a result of overburden material being replaced on this structure. In order to determine the failure mechanism associated with the culvert, a series of numerical modeling analyses were carried out utilizing back analysis technique. The validity of the numerical model was justified by convergence measurements and observations carried out inside the culvert as overburden material being replaced on the stable part of this structure. Finally, based on the numerical model developed, the stability of other culvert alternatives that could be used in future projects were evaluated considering different embankment conditions (positive projecting and negative projecting), bedding conditions (impermissible, ordinary, first-class and concrete cradle), culvert shapes (box and circular) and dumping conditions.

The production of multi-component cement from clinker and two additives such as trass and blast furnace slag has now spread throughout the world. These additives are generally interground with clinker to produce a composite cement of specified surface area. The grinding stage is of great importance as it accounts for a major portion of the total energy consumed in cement production and also as it affects the quality of composite cements by the particle size distribution of the individual additives produced during grinding. This thesis study was undertaken to characterize the breakage properties of clinker and the additives trass and slag with the intention of delineating their grinding properties in separate and intergrinding modes. Single particle breakage tests were conducted by means of a drop weight tester in order to define an inherent grindability for the clinker and trass samples in terms of the median product size ( ). In addition, a back-calculation procedure was applied to obtain the breakage rate parameters ( ) of perfect mixing ball mill model using industrial data from a cement plant. Kinetic and locked-cycle grinding tests were performed in a standard Bond mill to determine breakage rates and distribution functions for clinker, trass and slag. Bond work indices of these cement components and of their binary and ternary mixtures were determined and compared. Attempts were made to use back-calculated grinding rate parameters to simulate the Bond grindability test. The self-similarity law was proved to be true for clinker and trass that their shapes of the self-similarity curves are unique to the feed material and independent of the grinding energy expended and overall fineness attained. The self-similar behaviour of tested materials will enable process engineers to get useful information about inherent grindability and energy consumption in any stage of the comminution process. The parameters, and indicating the degree of size reduction were defined with different theoretical approaches as a function of energy consumption by using single particle breakage test data of clinker and trass. The breakage distribution functions were found to be non-normalizable. On the other hand, the breakage rate functions were found to be constant with respect to time but variable with respect to changing composition in the Bond ball mill. These variations are critical in computer simulation of any test aiming to minimize the experimental efforts of the standard procedure. As a result of the back calculation of breakage rate parameters for clinker and trass samples in the Bond mill, no common pattern was seen for the variation of the rate parameters. Therefore, computer simulation of the Bond grindability test did not result in an accurate estimation of the Bond work index.