Understanding, Developing and Exploiting Cobalt Superalloys for Discs

In 2005, the discovery of a new intermetallic was announced in Science, Co3(Al,W), together with evidence Co-Co3(Al,W) alloys might have a higher temperature capability than in the Ni-base superalloys used in jet engines. It was claimed that this would allow a new generation of gas turbine alloys to be developed beyond Ni-base superalloys.

However, these alloys and those developed since have densities that are too high and oxidation resistance that is too poor for engineering application. Over the past two years, as part of the Rolls Royce - EPSRC Strategic Partnership, two PhD students at Imperial College have demonstrated that a lower density, oxidation resistant Co-base superalloy can be developed, which still has a superior temperature capability.

The aim of the current work is to develop the underpinning science underlying the effect of alloying on the creep behaviour of these alloys, which is principally a function of the way in which deformation-related defects called dislocations move through the structure and in particular the way they interact with the intermetallic precipitate. Our recent work has demonstrated that this interface is not sharp and instead has a width that varies with alloying from 0.4 to over 2nm, a factor of over 5X. It is expected that this will increase the rate at which these intermetallic precipitates grow in size - from 20nm to over 200nm - in service, which in turn is a major driver for strength and creep resistance.

Knowledge - Scientific Advances and Techniques

Conventional nickel-base superalloys are mature yet their temperature capability is the fundamental limit on the efficiency that can be attained by gas turbines. Therefore developing and understanding a successor alloy system - the Co-base superalloys - will enable developments in other gas turbine technologies such as ceramic coatings, combustion research and the fluid-mechanical design of turbomachinery.

One of the major subthemes of this proposal is that it shows leadership of the community by integrating our recent technique developments to achieve scientific insight into a phenomena and to articulate its consequences.

Policy and Quality of Life

In helping to mitigate CO2 emissions, the work developed here will help forestall the consequences of global warming, having a global impact on emissions. With growth in the BRICs and North American emissions being such a large contributor to this global pollutant, even small improvements here are arguably more significant that any UK-centric initiatives, especially now that the UK government is becoming more focussed on shale gas.

In aerospace sustained competitive advantage is obtained by cumulative capabilities - deep experience of design, underpinning science and service support, and this is why the UK aerospace sector has remained competitive. The work here provides us with an opportunity to showcase this to the policy community, deepening its understanding of research translation.

This sort of safety-critical work will be of great interest to certification authorities such as the US AFRL, FAA and CAA. The results will therefore influence industry design and global turbofan certification practice, improving air safety for the travelling public.

Economy - inward investment, wealth creation, products and services

Manufacturing remains the third largest sector in the UK economy and has continued to grow. There is a clear trend in low value, high volume manufacturing moving to developing countries while in the UK the higher technology areas generate the better Gross Value Added returns. Aerospace is a global growth sector, contributing around 7.5% of global GDP, with traffic growing faster than the global economy (5-6% pa). Rolls Royce is the UK's largest export business with revenues of £11bn p.a., >75% of which is civil and exported, and over 40,000 employees, most of whom are in the UK.

Co superalloys promise a >100 C improvement in usable temperature capability. In the jet engine business, 0.5% engine fuel efficiency is worth around US$10m/yr in cost and CO2 to the airline per plane, and is the difference between success and failure for an engine programme, being proportional to approx. 10 C in turbine entry temperature. Clearly, success in this programme would provide a sustained source of competitive advantage to Rolls Royce if successfully taken through the subsequent >£1m alloy qualification programme.

People - skills and people pipeline

UK metallurgy and STEM more generally continues to find recruitment problematic. Therefore with the rebalancing of UK attitudes away from financial services and towards manufacturing, it is currently timely to use research outcomes to evangelise society and especially teenagers to build the people pipeline.
However, the reach that individual research projects can have is necessarily limited. Therefore we engage with other projects that target teenagers to deliver this impact, such as the Naked Scientists and Exscitec.

The PDRAs employed will also provide people trained in mechanisms-based, linked alloy and fundamental science development, together with linked computational modelling for insight. With much excitement around ICME approaches and initiatives such as the US Materials Genome Initiative, people with this outlook will be in significant demand.