Dr Martin Jackson of The University of Sheffield explains how his team is shaping the future of titanium alloy processing. The University of Sheffield is enabling a future step-change in the economics of titanium through alloy development with Metalysis, providing a manufacturing route – FASTforge – for the growing aerospace market.
Titanium alloys have strengths comparable to steel but with half the density, as well as excellent corrosion resistance and biocompatibility. However, its major drawback is the production cost, which confines the metal largely to the aerospace industry where properties such as low density, high levels of strength and fatigue resistance is essential.
With growing demand for air travel, civil aircraft, which are increasingly being manufactured from carbon composite fuselage and wing structures, are set to rise over the next decade. There will be a corresponding increase in titanium tonnages for fasteners and high strength forgings due to titanium’s compatibility with carbon. But with current world mill production capacity at approximately 150,000 tonnes, there will be restricted availability for the aerospace sector unless additional sources come online.
However, high costs and limited supply associated with titanium could be a thing of the past, thanks to the Sheffield Titanium Alloy Research group (STAR) who are quietly revolutionising titanium alloy production from rutile sand extraction through to novel processing routes for mill product and net shapes. With UK industry partners such as SAFRAN Landing Systems, Metalysis and Kennametal (UK) they aim to generate lower cost, novel titanium alloy components with properties that are equivalent to commercially available alloys in three steps.
Step 1: Rutile to novel titanium alloy powder in one step
We are working closely with Metalysis, a spin-off technology company, to exploit a solid state electrolytic process to produce titanium alloys directly from synthetic rutile feedstock. Current titanium production is a multi-step method of the carbo-chlorination of oxides, fractional distillation of chlorides, magnesium reductions before vacuum arc remelting stages.
High strength titanium alloys employed in aerostructural components require small additions of aluminium and transition metals to manipulate titanium’s allotropic nature and generate fine scale microstructures with excellent mechanical properties. Small additions of such elements naturally exist in the synthetic rutile separated from ilmenite - a black sand commonly found in the earth’s crust.
However, an alternative, lower cost extraction route alone is insufficient to provide a sufficient step change in cost. It is the downstream processing of such powder into usable mill product that will have the largest impact on cost reduction.
Steps 2 and 3: FAST-forge - powder to shaped component in two steps
We have developed hybrid manufacturing processing technology that consolidates titanium feedstocks into near net shapes in two solid-state steps, as opposed to the conventional forty or so processing steps.
This FAST-Forge downstream consolidation route exploits field assisted sintering technology with traditional precision hot forging processes. FAST has advantages over hot isostatic pressing as more rapid sintering can be achieved without the need for process-limiting steel canning and degassing steps. In addition, the hybrid process has benefits for material utilisation and reuse of machined swarf, potentially leading to much improved buy-to-fly ratios: currently for some aerospace components, 90% of the forged titanium alloy is machined away to swarf.
Through their partners in both the aerospace and automotive industry, FAST-forge of titanium is one step closer to becoming the UK’s next world leading high value manufacturing capability, and a new source of low cost titanium components for a range of sectors.