Vat-photopolymerisation 3D printing silica-based ceramic cores used in investment casting of hot section parts for aero and power turbines

<p dir="ltr">The components such as turbine blades and nozzle guide vanes are broadly employed to extract energy from the hot gases surrounding them, while they might be one of the most critical and notable features of any jet ?engine or industrial gas turbine (IGT) installation. They have one of the most complex design features; they are being operated under the most arduous high-temperature environments for extended periods just below the melting point of their material, which is often made of high-temperature nickel- and cobalt-base superalloys. These components should be designed to be intricate and complex of near-finished shape with many cooling channels to withstand direct stresses and rapid temperature transients at diversified points, which positively influences the engine's efficiency. Therefore, the blades/vanes portray unique technological challenges in the manufacturing processes. Investment casting is currently the most commonly associated operation to produce these components, and ceramics cores made by ceramic injection moulding are widely employed as sacrificial inserts to manufacture intricate internal cooling passages in the process of turbine blade casting. The choice of material and production process is led by a few design parameters such as optimum mechanical strength and porosity, high dimensional stability, low coefficient of thermal expansion, high thermal shock resistance, the possibility of complex shape forming, and removal ability leaching. Previous studies reduced the list of possible choices of ceramic materials to fused silica, zirconium silicate, and alumina. However, the main challenge in the ceramic core process is to shape parts due to the inherent hardness and brittleness of ceramic materials; hence traditional manufacturing methods have been reached their final capacity and are not capable of fabricating more complex structures with detailed features where particularly needed in turbine engine industry.</p><p dir="ltr">Additive Manufacturing (AM), also known as three-dimensional (3D) printing, presents a unique advantage to form highly complex geometries never possible with traditional techniques and is exceptionally advantageous where flexibility is required in the manufacturing process. Among potential AM ceramic techniques, vat?photopolymerisation (VPP) is the most capable technology to produce ceramic cores where high mechanical properties, resolution and dimensional accuracy are required and offers high process speed easy to scale up the manufacturing process. However, when this technology is considered for manufacturing ceramic core used in the investment casting of blades/vanes, there is still a substantial gap in the AM knowledge and practice, which implicates needs for future studies in the AM manufactured ceramic core components. Therefore, this PhD thesis aimed to select, design, optimise and develop ceramic suspension and a VPP process for such applications and their industrial scalability as a feasible production method by implementing cheap commercial solutions. The contribution to the knowledge of this study is further exploring and a better understanding of the fundamentals in the development of ceramic suspensions such as monomers or monomer blends used for ceramics, dispersion and stabilisation mechanisms, their curing or cross-linking performance with reference ceramic powders and optimum solid loading. The research also provides insights into how to optimise the formulation of ceramic suspensions by defining critical process parameters in the VPP printing of ceramic cores, which are rheological behaviours of suspensions during printing cycles, mechanical resistance of green parts, induced separation forces on cured layers, printing temperature and mechanical properties of sintered parts. Developing a printable ceramic suspension mixture and identifying the most suitable processes parameters with cheap commercial ceramic powders and mainstream VPP printers could lead to new approaches through this scalable printing method, enabling fabrication of ceramic cores without any design restrictions and exploring the science behind improving the inlet cooling systems of blades/vanes. This PhD thesis is divided into four published/submitted research papers and establishes a strong link between each other. Their final combination results in a novel ceramic suspension made of conventional ceramic powders that can be used to print and successfully sintered very complex-shaped ceramic cores in any type of hobby VPP printers such as Anycubic® Mono S, one of the cheapest in the market</p>