The production of Ti-Fe alloys using solid-state, powder-based extraction and processing technologies

This thesis demonstrates the ability to create Ti-Fe alloys using two solid-state, powder-based technologies: the FFC-Cambridge process and field assisted sintering technology (FAST). Together, these technologies have many proposed benefits for Ti alloy production compared to the conventional route, with potential to significantly reduce the cost of Ti, provided they are effectively scaled up. This work assesses these technologies for the production and processing of Ti alloys, whilst focussing on inexpensive Fe as the major alloying element.
Ti-Fe diffusion couples produced using FAST highlighted that the Fe diffusion rate into Ti increases dramatically from 800–1000°C. Chemical and microscopic analysis revealed
that an intermetallic layer formed at the interface, and a gradual decrease in Fe content resulted in microstructural layers of α, α+β and β Ti, due to varying β stabilisation.
FAST was then used to consolidate pseudo-binary Ti-Fe alloy powders produced via the FFC-Cambridge process and derived from mixtures of synthetic rutile and Fe2O3.
Although the powders were chemically heterogeneous, FAST provided the conditions to consolidate to >99% theoretical density and facilitate the Fe diffusion required to generate
homogeneous microstructures. Alloys containing up to 9 wt.% Fe were produced, but final compositions were inconsistent compared to the amounts of Fe2O3 used, indicating
Fe loss to the electrolyte. Despite poor ductility of the alloys due to high O contents, this production route combining the FFC-Cambridge process with FAST shows promise,
with this work representing a proof of concept which can be improved upon by future optimisation.
Solid-state alloying of blended Ti and Fe powders was also investigated, establishing that homogeneous, fully dense alloys with compositions up to Ti-10Fe can be produced using FAST with no intermetallic phase formation. These alloys also exhibited low ductility, although using an alternative, lower O content, Ti powder could improve the results.