A novel solid-state processing route to generate cost-effective titanium alloy components

This thesis demonstrates progress towards a step-change in the economics of titanium. Titanium's properties make it desirable to designers, but it is frequently overlooked due to high costs; making research into reducing costs of considerable interest. Examining the literature shows cost reduction possibilities in two main areas; extraction and downstream processing. Lower-cost extraction has previously received much attention, but in isolation will not produce the required reductions. Powder metallurgy techniques allow near net shape (NNS) production with limited material wastage and processing steps; also allowing utilisation of powders/particulates produced by many developing extraction methods. Combining products from alternative extraction with novel solid-state downstream processing has potential to produce truly cost-effective titanium alloy components.
Chapter 4 establishes field assisted sintering technology (FAST) as a rapid and effective method to fully consolidate commercial and developing titanium alloy powders, with a wide variety of chemistries, morphologies, and sizes, including material from the Metalysis FFC process. FAST scalability was successfully tested by producing a 5.5 kg, 250 mm diameter, specimen. Chapter 5 shows that titanium alloy preforms produced via FAST behave equivalently to conventionally processed melt, multi-step forged, products. The shapes and microstructures produced were not those typically required for components. Consequently, chapter 6 investigates the proposed cost-effective processing route of producing wrought microstructures in two steps from powder, which has been termed FAST-forge. A fully dense, microstructurally homogeneous, shaped preform billet formed via FAST was finished with a precision one-step forging operation that refined the microstructure, verifying the FAST-forge concept at laboratory-scale.
It is anticipated with further development, and by utilising finite element modelling, that it will be possible to produce semi-complex NNS components with competitive mechanical properties in just two steps. Therefore, FAST-forge has potential to be disruptive technology that could enable the desired step-change in the economics of titanium.