Towards the fabrication of titanium aerospace structural components via cold spray additive manufacturing

Cold spray additive manufacturing (CSAM) is a solid-state deposition process capable of producing metallic 3D structures at rates of kg/hour. CSAM has been used as a coating and repair system in various industry sectors (mainly aerospace and automotive). In the aerospace industry, various additive manufacturing (AM) systems have been used to produce lightweight aerospace structural components (LASCs); thus, there is interest in using CSAM as it can process titanium and its alloys without a specially controlled environment, e.g. electron beam melting requires a vacuum to process titanium due to its sensitivity to oxidation. The kinematic motion of the cold spray gun and the generally high mass build rate per unit area significantly influence a component's microstructure and thus, mechanical properties. Postprocessing a CSAM component also profoundly impacts its mechanical behaviour by changing its balance of strength to ductility, affecting both its tensile properties and fatigue resistance. With the rigorous standards that components must meet for aerospace structural components, quantifying the relationship between process parameters, microstructure, and mechanical properties of CSAMed titanium is critical to safe and cost-effective fabrication. This thesis aims to (i) quantify some of these relationships, for which it required an in-depth examination of the effect of robot toolpath planning and post heat-treatment on microstructure and mechanical properties of simplified cuboidal parts, and (ii) use this knowledge to efficiently manufacture a demonstrator titanium LASC with real-world geometrical complexity and mechanical performance. The initial part of this thesis establishes the design of a base case geometry for this part via finite element analysis (FEA), for which mechanical and fatigue testing can be carried out. The microstructure and properties of multiple titanium metal matrix composite combinations were analysed, and a suitable material candidate was selected. Ti – 10TiC was selected as the feedstock material as it provided higher strength compared to unreinforced CP Ti without any significant ductility loss and a chemically stable system. As the feedstock material has been established, toolpath planning strategies to produce complex 3D geometry were studied by producing samples using different toolpath planning strategies. Processing conditions were narrowed to those in which the criteria established in standards for aerospace structural components are met and then used to manufacture the aerospace demonstrator part. From those results, simulation and topology optimisation were performed in order to minimise the weight of the aerospace demonstrator part while still being manufacturable via CSAM. With the findings in this study, it gives insight to engineers and designers on what parameters and their effects on the components to consider when producing a complex 3D component using CSAM.