The crystallographic texture of a material has a direct impact on its mechanical and functional properties. As a result, texture control is an imperative part of manufacturing processes, especially those involving plastic deformation, such as rolling, which significantly impact crystallographic texture. The exact mechanisms and underlying causes behind such texture evolutions are not well understood. This study investigates the effect of initial disorientation topology on plastically deformed texture, with the help of mean field crystal plasticity simulations performed using the ALAMEL model. The simulated textures are compared to experimentally measured textures of IF steel samples with symmetric rolling reductions of 55 % and 83 %. The results indicate a clear distinction between low disorientation topologies and high disorientation topologies, most evident at high rolling reductions. The study aims to incorporate the disorientation information into the ALAMEL simulations, by re-ordering textural input orientations. The Monte Carlo algorithm is used in addition to the Hungarian Algorithm to re-order orientations based on pre-set disorientation angles. A comparison between the two re-ordering algorithms is also performed, and the Hungarian algorithm is found to have a disorientation distribution closer the ideal result. A comparison between the two yields minimal differences, with the difference between the two results being the error index local minima for minimum disorientation evolved textures and average disorientation (between 35°. Local maxima for error index comparisons are observed for very high disorientation values of over 60°. In the present study, we also result spread for similar disorientation topologies orders to discount the randomness associated with such a process. Thus, multiple files are created with largely similar disorientation characteristics but different grain orders. An overlap is observed for high disorientation simulations, at a higher frequency for lower rolling reductions. The deviation of obtained results is also highest for a disorientation angle average of 15°. The simulated texture comparisons between textures with modified and unmodified texture disorientation topology also indicate a higher disparity with minimum disorientation modified texture. A convergence is observed at a disorientation value between 35° and 40°, close to the disorientation average of the unmodified texture, and an overlap is observed at higher disorientation values. The valorisation of such a technology is also considered in this study. The current study precedes applied research and is assessed as a level 2 on the technology readiness scale, in danger of facing the ‘valley of death’. This is owing to fading interest and funding unless the private sector see’s value in the technology. The domain most aligned for the application of such technology is electrical steels, which is set to see a large increase in demand and will play a significant role in the energy transition and move towards electrical mobility. The high cost of development and price sensitive market serve as barriers of entry, and entry into the niche beachhead market of DC converters for next generation ‘more electrified aircraft’ is determined to be an appropriate valorisation strategy. The study also proposes a ‘way to market’ strategy, drawing parallels with other high tech and high value material industries, to determine ‘critical partnerships’ with high levels of integration in addition to leadership in materials and manufacturing development as key factors for a successful market entry.

In our modern world, where computers, mobile phones and many other applications have become indispensable, there is a growing need for high precision machines in order to be able to produce these technologies. For these complex high precision applications it is important to understand the fatigue properties of the materials used to prevent premature failure, as these materials are subjected to large numbers of stress cycles. A material that is used for high precision applications is Ti-6Al-4V, as its material properties are highly adaptable and can be fine-tuned for a wide range of applications. Material fatigue due to stress cycles knows two stages: crack initiation and crack propagation. This research focuses on the latter and looks into the influence of microstructural features on crack propagation in Ti-6Al-4V. The influence of the microstructural features is tested by applying a load shedding method to form cracks in Ti-6Al-4V samples. These cracks are analysed with Scanning Electron Microscopy (SEM) and Electron BackScatter Diffraction (EBSD) in order to relate the microstructural features to the crack path. There are two main microstructural features found to have a large influence on the fatigue crack propagation in Ti-6Al-4V. The first of these is the Schmid factor, which relates the applied stress to the slip system available. As there are only a small amount of slip systems available in Ti-6Al-4V and limited crack path propagation opportunities, large crack deflections can be the result. The second microstructural feature found to have a large influence is the misorientation angle of the grain boundaries. When the misorientation angle is large enough, a shift from transgranular cracking to intergranular cracking is observed. Intergranular cracking can cause deviations of the crack path around the grains and the formation of secondary cracks. The deviations in crack path as a result of a low Schmid factor and a high misorientation angle extend the fatigue life of the material. The Schmid factor was found to have a large influence on crack deflections observed, whereas the high misorientation angles were mostly found around sites where bifurcation occurred, especially at lower applied stress ranges. This study proposes that the influence of the microstructural features on fatigue crack propagation in Ti-6Al-4V can be expressed as two probability functions describing crack deflection and bifurcation. The probability of a crack deflecting is relatively high for a lower Schmid factor, a high misorientation angle and a low deflection angle. The probability of bifurcation is relatively high when a near-threshold stress intensity range is applied and also for a high misorientation angle and a low deflection angle.

This thesis is a comparative study of the Thermo-Mechanical Fatigue (TMF) performance of different grades of SiMo nodular cast iron for heavy-duty diesel engine exhaust gas manifold applications. The TMF performance of the current SiMo variant used to manufacture exhaust manifolds - SiMo 5.10 (C-3.25Si-4.45Mo-0.76), is compared with that of the variants SiMo 4.05 (C-3.22Si-4.66Mo-0.56) and SiMoNi (C-3.3Si-4.5Mo-1Ni-1.3) by performing three out-of-phase (OP) TMF test series under partial constraint conditions. A benchmark TMF test series in the temperature range: 50 ˚C to 550 ˚C with a hold time of 30 s at 550 ˚C showed that SiMo 5.10 had relatively better performance due to development of lower mechanical crack driving forces compared to other variants. However, a long holding time of 600 s at 550 ˚C saw a larger decrease of average TMF lifetimes for SiMo 5.10 than that of SiMo 4.05 despite similar crack driving forces. An investigation of the stress relaxation during TMF of the two variants showed that the SiMo 4.05 performs better during long hold time due to better stress relaxation properties. The SiMoNi variant which is very brittle at low temperatures was found to fail by a fracture by overloading mechanism taking over quite early in the fatigue cycle; which is confirmed by examination of the fracture surfaces and numerical estimations. This also explained the low lifetimes and scatter in previously performed TMF tests under total constraint conditions. The TMF test series performed in the temperature range: 150 ˚C to 550 ˚C with a hold time of 30 s at 550 ˚C found that a heat-treatment seemed to reduce the TMF performance of the SiMo 5.10 variant. Metallographic investigations and hardness measurements of as-cast and heat-treated materials revealed that the distribution of the Mo-rich phase from the grain boundary regions into the matrix due to an annealing heat-treatment seemed to affect the TMF performance.