The drive to an environmentally sustainable future will have a great impact on the aerospace industry. This has already been acknowledged by the Chief Technical Officers of the seven largest aerospace companies when they signed a joint statement at the Paris Airshow this year outlining the industry approach to support a more sustainable future. The approach outlined has three strands that will be pursued: more efficient gas turbines, biofuels and the electrification of the power train. Whilst there is a current drive to use batteries to power aircraft for routes of up to 1000km the current studies the options for transcontinental flights are being focussed on hybrid electric power. (e.g. Visions of the future: hybrid electric propulsion, Cheryl Bowman AIAA Aircraft Electric/Hybrid-Electric Power & Propulsion Workshop, July 28, 2016, and Reed A. Danis, Michael W. Green, and Jeffrey L. Freeman Examining the Conceptual Design Process for Future Hybrid-Electric Rotorcraft NASA/CR-2018-219897)

In the cases of the more efficient gas turbines and the hybrid electric solutions a small, highly efficient gas turbine core will be needed. As the high pressure turbine blade is the defining component for the efficiency of the gas turbine the manufacture of these components will be key reaching these efficiency targets. In fact the traditional single crystal casting of turbine blades will not only be required for these aircraft with projected market entry dates of 2035 but it will need to be enhanced and improved to deliver the small, highly complex turbine blades which are being planned.

As the conditions seen in the heart of the gas turbine have increased over the years the stresses within the blades and the temperatures seen by them have pushed the materials closer to their limits. The single crystal cast material has been seen as the ideal solution to these higher stresses and hotter temperatures. Now, however, it is not the laboratory measured properties which determine the in-engine performance but the casting defects which come from trying to align 6x1024 atoms in a single blade which are becoming more critical to the life calculations. These atomic misalignments can be seen in the components as second grains and the majority of single crystal components in service have these grains but they are expected to be benign as they have only a small misalignment. However the study of secondary grains in single crystal materials has not been widely undertaken as the material is not supposed to contain a second grain in service and the samples are difficult to manufacture.

The Fellowship will have two broad goals: to improve the single crystal casting process for complex, small features and to look at the formation of grain defects and predict the impact of them on the properties of the material. As the features seen in the casting will drive the generation of second grains these two goals are interlinked. My experience in casting real components in an industrial environment and also my knowledge of the direction of design concepts will allow this work to be appropriate to industry but academic in nature.

As these projected hybrid electric engines will begin their lengthy design and testing phase from 2025 onward this Fellowship is well timed to deliver the scientific understanding needed prior to this date.

Potential Impact:
World air travel in 2025 is forecast to have increased by 85% compared to 2005 and to continue to increase at the same rate beyond. However, air travel is polluting and a significant contributor to the population's carbon footprint.. Programmes such as Clean Sky have been implemented to address these issues and will be nuilt upon to deliver the targets which will come from this new drive. It is forecast that through such programmes and developments the emissions will not increase proportionately with the increase in passenger miles, a 64% reduction between 2005 and 2025 being targeted. The aviation industry is beginning to feel this change and was amply demonstrated by the Chief Technical Officers of the seven largest aerospace companies when they signed a joint statement at the Paris Airshow this year outlining the industry approach to support a more sustainable future. Whilst this approach has been seen often within the individual companies this is the first co-ordinated alignment of strategies to use technology to drive a reduced environmental impact. This project is seen as a potential aid to achieving this forecast, allowing people to fly significantly more miles without dramatically increasing emissions. The project therefore will address a number of societal requirements through increasing flight efficiency. These technologies will operate internationally and the project is purposeful in addressing government policy. Aircraft emissions influence the quality of life and the long term well-being of the environment and this project goes some way to addressing this aspect.
Efficiency improvements in aero engine gas turbines can be achieved in a number of ways; increasing the core temperature in the engine, reducing the amount of cooling air required to maintain a particular temperature cycle or removing weight from the engine or aircraft; this project targets the first two. As the drive to smaller component features and higher stresses in those components will require the manufacturing capability to improve, then this work is initially targeted at engine manufacture, and thus predominantly at Rolls-Royce in the UK alongside the UK casting supply chain, the benefits will be retained within the UK high value manufacturing sector.
The single crystal casting business in the UK is worth around £400M and currently world leading in terms of the application technology and innovation. However, as the components become more difficult to manufacture then the need for highly developed solidification science to drive robust processes will be needed to maintain this position. Other nations are developing single crystal casting technology and, whilst they are currently not at he capability of the UK and US, it is crucial that the UK retains the cutting edge to remain competitive in both the design and manufacture of turbine components.
This proposal will support the manufacturing of next generation single crystal components by providing solidification science as the foundation of robust manufacturing processes. This will enable the UK aerospace industry to remain at the forefront of industry as it is today for the provision of next generation hybrid electric solutions for air travel.