Understanding, Developing and Exploiting Cobalt Superalloys for Discs

Lead Research Organisation: Imperial College London
Department Name: Materials

Abstract

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.

Planned Impact

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.
 
Description We developed oxidation resistance in this family of Co-Al-W alloys for the first time, and reasonable (<8.5) density, which are key enablers for their practical application in jet engines. This required us to also understand and balance the phase stability to retain and develop an fcc gamma matrix with L12 strengthening nanoscale precipitates. We also have done much work on their manufacturability for a powder metallurgy processing route. The dislocation and creep behaviours, and the matrix strength, are critical to taking this work to the next stage.
Exploitation Route This work has been citied by C Sudbrak (NASA) and A Suzuki (GE) as being the most credible work in developing real alloys in this fast-growing field (>50 participants in a yearly symposium). It is being rapidly followed up by fast-followers at Erlangen (Neumaier), IISc Bangalore, GE, and so on - who are citing our papers from this grant.
Sectors Aerospace, Defence and Marine,Energy

 
Description This project is continued in the Rolls-Royce strategic partnership (EP/M005607/1). Two patents have been filed on alloys developed out of this project, that are currently being developed and evaluated for future jet engines.
First Year Of Impact 2015
Sector Aerospace, Defence and Marine,Energy
Impact Types Economic

 
Description SPII
Amount £7,939,564 (GBP)
Funding ID EP/M005607/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 10/2014 
End 09/2019
 
Description Cambridge University 
Organisation University of Cambridge
Department Department of Materials Science & Metallurgy
Country United Kingdom 
Sector Academic/University 
PI Contribution We have made test alloys and helped with their deformation processing
Collaborator Contribution Drs Howard Stone, Cathie Rae and Nick Jones have facilitated making test alloys with us.
Impact Joint publications (see publication list), joint grants (see EPSRC grants on the web), joint patents (see IP)
Start Year 2010
 
Description Rolls-Royce plc 
Organisation Rolls Royce Group Plc
Country United Kingdom 
Sector Private 
PI Contribution .
Collaborator Contribution .
Impact .
 
Description Swansea 
Organisation Swansea University
Department College of Engineering
Country United Kingdom 
Sector Academic/University 
PI Contribution We provided samples for Swansea to test, contributing to their PhDs on this topic, and evaluated the samples post-testing
Collaborator Contribution Swansea performed creep and fatigue tests on our sampled
Impact Joint publications; contribution to alloy development activities that have resulted in patents
Start Year 2014
 
Title Alloy 
Description New Co superalloy for gas turbine discs 
IP Reference EP2821519 
Protection Patent application published
Year Protection Granted 2014
Licensed Yes
Impact This patent is the first in a family protecting future Co-base superalloys for application as turbine discs in jet engines; a critical part of Rolls-Royce's future jet engine development strategy
 
Title Co alloy 1.3:1 
Description A Co-Ni superalloy for jet engine turbine discs 
IP Reference Invention submission 12070 to GB patent office (12 Dec 2014) 
Protection Patent application published
Year Protection Granted 2016
Licensed Yes
Impact This is the second in a family of patents that protect a group of Co superalloys for future jet engine turbine discs, a key part of Rolls-Royce's product development strategy.