Typically, pure TiO 2 in pellet form has been utilised as the feedstock for the production of titanium metal via the solid state extraction FFC process. For the first time, this paper reports the use of loose synthetic rutile powder as the feedstock, along with its full characterisation at each stage of the reduction. The kinetics and mechanism of the reduction of synthetic rutile to a low oxygen titanium alloy have been studied in detail using a combination of X-ray diffraction, scanning electron microscopy, oxygen analysis, and X-ray fluorescence techniques. Partial reductions of synthetic rutile enabled a reaction pathway to be determined, with full reduction to a low oxygen titanium alloy occurring at 16 h. Major remnant elements from the Becher process within the feedstock were followed throughout the process, with a particular emphasis placed on the reduction behaviour of iron within the alloy. Although impurities such as Fe, Al, and Mn are found in the feedstock and alloy, no major deviations from previously reported reaction mechanisms and phase transformations utilising a pure porous (25-30 % porosity) TiO 2 precursor were found. Following reduction, the titanium alloy powder produced from synthetic rutile (approx. 3500 ppm oxygen) has been consolidated via an emerging rapid sintering technique, and its microstructure analysed. This work will act as the baseline for future alloy development projects aimed at producing low-cost titanium alloys directly from synthetic rutile. Producing titanium alloys directly from synthetic rutile may negate the use of master alloy additions to Ti in the future.

Mechanical property data of a low-cost titanium alloy derived directly from synthetic rutile is reported. A small-scale testing approach comprising consolidation via field-assisted sintering technology, followed by axisymmetric compression testing, has been designed to yield mechanical property data from small quantities of titanium alloy powder. To validate this approach and provide a benchmark, Ti-6Al-4V powder has been processed using the same methodology and compared with material property data generated from thermo-physical simulation software. Compressive yield strength and strain to failure of the synthetic rutile-derived titanium alloy were revealed to be similar to that of Ti-6Al-4V.

Combining the FFC-Cambridge process with field-assisted sintering technology (FAST) allows for the realisation of an alternative, entirely solid-state, production route for a wide range of metals and alloys. For titanium, this could provide a route to produce alloys at a lower cost compared to the conventional Kroll-based route. Use of synthetic rutile instead of high purity TiO2 offers further potential cost savings, with previous studies reporting on the reduction of this feedstock via the FFC-Cambridge process. In this study, mixtures of synthetic rutile and iron oxide (Fe2O3) powders were co-reduced using the FFC-Cambridge process, directly producing titanium alloy powders. The powders were subsequently consolidated using FAST to generate homogeneous, pseudo-binary Ti–Fe alloys containing up to 9 wt.% Fe. The oxide mixture, reduced powders and bulk alloys were fully characterised to determine the microstructure and chemistry evolution during processing. Increasing Fe content led to greater β phase stabilisation but no TiFe intermetallic phase was observed in any of the consolidated alloys. Microhardness testing was performed for preliminary assessment of mechanical properties, with values between 330–400 Hv. Maximum hardness was measured in the alloy containing 5.15 wt.% Fe, thought due to the strengthening effect of fine α phase precipitation within the β grains. At higher Fe contents, there was sufficient β stabilisation to prevent α phase transformation on cooling, leading to a reduction in hardness despite a general increase from solid solution strengthening.

Utilising novel extraction and processing technologies allows for the realisation of an alternative titanium alloy production route, with many benefits over the traditional Kroll-based one. The route proposed has the potential to reduce the cost of titanium and offers the ability to create alloys which are difficult to make conventionally. It combines the Metalysis Process, an electrolytic metal extraction technique, with field assisted sintering technology (FAST), a rapid and effective solid-state sintering technique. The Metalysis Process reduces metal oxide powders directly into metal powders, which can then be consolidated using FAST. Using synthetic rutile (SR) as the feedstock, compared to pigment grade rutile and TiCl4, further reduces the cost of titanium produced via this route. This research investigates the use of this route to create a range of pseudo-binary Ti-Fe alloys, by co-reducing SR with iron (III) oxide (Fe O ). Various techniques were used to analyse the feedstock, reduced alloy powders and consolidated material post-FAST to 23 determine chemistry and microstructure.

No abstract