Sky is not the limit for titanium composites

Recent actions are set to change all that, however, as a consortium of supply chain companies and end users begin a collaborative research and development project to make a new level of technology maturity and cost-effective production capability available, as Neil Calder finds out.
In March this year, the UK Technology Strategy Board (TSB) announced it was going to fund the TiCCRaMM project in order to move titanium composite manufacturing on to the next stage of capability readiness.

Currently, the use of TMCs is sitting in the technology readiness level range 3-6, somewhere in the gap between having the technology building blocks available and knowing how to use them in series production applications. The missing link is not in the ability to create very high performance structures, as a range of aircraft parts have already been qualified for flight, but instead in the establishment of a viable supply chain which will make these products happen on a commercial scale rather than in the laboratory. End user applications have been constrained by the lack of production capacity in a classic ‘chicken and egg’ circular argument: it is demand which drives capacity but also the existence of the production capability which will trigger demand.

The actual process is carried out by Farnborough-based TISICS, whose technology provenance extends back to a part of UK defence research not dissimilar to that which was responsible for early carbon fibre production and who is the only supplier of this technology outside the US. 100-140µm diameter structural fibres are created by depositing SiC onto 15µm tungsten filaments from gaseous silane in a continuous reaction process. The titanium matrix is introduced via foils and consolidated by hot isostatic pressing (HIP). Typically this produces a composite material with 35% volume fraction of fibres. Previously the technical activity focus has been in material development, but now, with a robust continuous fibre production capability the supply chain can look further towards real commercialisation of components incorporating this very high performance technology.

Surpassing steel

Specific strength and stiffness of TMCs are both around double that of 300M steel, a fairly typical choice for ultra high strength aerospace applications. Mass savings have proven to be about 30-40% for the direct substitution of existing parts, but designing for the properties of TMC from the outset can increase this to around 40-50%. Nothing comes without a price however, as depending on factors like physical complexity the cost projection range at full production capacity for TMC components is between two and five times that of the high strength steel alternative.
The expensive parts of the manufacturing process for any realistic production volume are the HIP tooling and fibre/matrix lay-up. Novel tooling systems and automated handling processes will be required to enable the cost-effectiveness of solutions and this is where much of the production process development effort within the TiCCRaMM project is to be centred.

The action is not about developing new materials technology: that has already been done on previous projects like the TSB Integrated Wing and EC FP7 VITAL. These projects have demonstrated the performance benefits and application possibilities for fibre reinforced titanium composites. TRL levels up to 6 have been achieved for aerospace components from brakes through to engines. Now the manufacturing capability readiness level needs to be addressed to achieve both production economics and volume production levels required for aerospace and other sectors. Once the methodologies are in place and a robust supply chain established there are potential opportunities in series production for civil aerospace from about 2015.

The TiCCRaMM project will look at the production routes for both smaller, high volume parts and for the larger, low volume, high load parts in the region of 100 to 150mm diameter and 1.5m+ long which are typical of many of the structural components in aero engines, landing gear and spacecraft. These are not intrinsically low cost markets, but the aim is to deliver high performance in a cost-effective way. Full size hydraulic actuator and side stay components for aircraft landing gear form the short-term physical focus for the process maturation work. Hydraulic actuator piston rods can be used to replace heavier steel parts and reduce the risk of corrosion as environmentally aggressive cadmium and chromium surface coatings are phased out. The side stays are large structural members typical of many parts currently made from aluminium, titanium or steel and at a target size for the TiCCRaMM project to address.

Aiming higher

TMCs are also looking to develop in applications beyond Earth’s atmosphere, as Reaction Engines in Culham is seeking to access affordable structural components for its Skylon spaceplane, whose design concept has recently passed a technical review by the UK Space Agency. In space applications, 1kg of structural mass saving equates to about another kg of propulsion saved and some 400kg of fuel in a very powerful virtuous circle.

The TiCCRaMM project consortium is addressing this through all parts of the TMC design and manufacturing supply chain from raw materials and processing through automation concepts and on to customer requirements. If successful it will enable the transition of TMC from technology push to requirements pull. Application areas beyond aerospace will enable volume manufacturing as well as applications in the marine, tidal/wave energy and oil and gas exploration sectors where there is need for the engineering features of TMCs.

TMCs are following the same development path as polymer composites. Initially very much a cottage industry with manual processes, the early applications don't in themselves quite make economic sense but have provided the foundation for application and market expansion. Automation of manufacturing process steps is attractive for the same reasons as with polymer composites, saving time in lay-up and ensuring a higher degree of consistency in the final positions of the fibres after consolidation of the matrix material.

This project will benefit from TSB funding as a pre-competitive action to advance the capabilities within the UK high value manufacturing supply chain through the full cycle from proof of concept to technically and commercially viable processes, although state aid limitations stop this before the point of product development.

For SMEs where leading edge technology developments are unable to attract funding from banks or venture capitalists until they have products, the TSB helps to stop technology going overseas or dying before it is picked up commercially. The exporting of carbon fibre composite technology definitely followed that trend, leaving the UK playing a relatively minor part in technology areas it originally defined. The UK has world class expertise in all aspects of metal matrix composites from materials through to applications and this high-tech industry has the potential to maintain a global position. However, this will only happen with the Government backing and patronage to get this to initial low rate production, building the inherent resilience and allowing the manufacturing sector to aid in the rebalancing that the UK economy needs. www.tisics.co.uk