Developing high Co-containing Ni-based superalloys with improved oxidation behaviour for future jet-engine applications

Ni-based superalloys are the alloys of choice for high performance, critical components used at the high temperature sections of gas turbines. In order to enable continuous efficiency gains, gas turbine manufacturers seek to push the operating conditions of Ni-based superalloys to ever higher temperatures and stresses. As a result, the environmental resistance of superalloys is increasingly becoming of critical importance as the elevated temperatures of future engines drives the components into harsher operating regimes. Consequently, the focus of future alloy design programs has identified environmental resistance as a key property for optimisation.

Previous research has shown that Ni-based superalloys with elevated Co concentrations possess properties capable of achieving the stringent operating requirements of newer generations of jet engines. In particular, the environmental resistance of such alloys, has been shown to outperform current state-of-the-art superalloys. This behaviour has been demonstrated despite reduced Cr and increased Ti concentrations, which have traditionally been markers of poor oxidation behaviour.

In close collaboration with Rolls-Royce plc, this project will focus on establishing the mechanisms that govern the oxidation behaviour in these materials and to inform future alloy design strategies for improved environmental resistance. This will be achieved through a comprehensive experimental matrix that will seek to firstly develop an in-house method of material manufacture, followed by oxidation trials and extensive characterisation utilising thermal analysis, microscopy and advanced diffraction techniques at national facilities. The project will also seek to identify the effects of pre-existing oxidation damage on the overall mechanical properties of the alloys. In parallel, thermodynamic and kinetic modelling approaches will be evaluated against experimental data and the models will be further informed and improved to account for alloys with elevated Co-concentrations. Consequently, the data generated through this project will provide Rolls-Royce with invaluable insights into current alloy behaviour and will inform future alloy development programs.

The EPSRC Centre for Doctoral Training in Advanced Metallic Systems was established to address the metallurgical skills
gap, highlighted in several reports [1-3] as a threat to the competitiveness of UK industry, by training non-materials
graduates from chemistry, physics and engineering in a multidisciplinary environment. Although we will have supplied ~140
highly capable metallurgical scientists and engineers into industry and academia by the end of our existing programme,
there remains a demonstrable need for doctoral-level training to continue and evolve to meet future industry needs. We
therefore propose to train a further 14 UK based PhD and EngD students per cohort as well as 5 Irish students per
cohort through I-Form.

Manufacturing contributes over 10% of UK GVA with the metals sector contributing 12% of this (£10.7BN [4,5]) and
employing ~230,000 people directly and 750,000 indirectly. It is estimated that ~2300 graduates are required annually to
meet present and future growth [5]. A sizeable portion of these graduates will require metallurgical expertise and current
numbers fall far short. From UK-wide HESA data, we estimate there are ~330 home UG/PGT qualifiers in materials and
~35 home doctoral graduates in metallurgy annually, including existing AMSCDT graduates, so it is unsurprising that
industry continues to report difficulties in recruiting staff with the required specialist metallurgical knowledge and
professional competencies.

As well as addressing this shortfall, the CDT will also impact directly on the companies with which it collaborates, on the
wider high value manufacturing sector and on the UK economy as a whole, as follows:

1. Collaborating companies, across a wide range of businesses in the supply chain including SMEs and research
organisations will benefit directly from the CDT through:

- Targeted projects in direct support of their business and its future development and competitiveness.
- Access to the expertise and facilities of the host institutions.
- Involvement in the training of the next generation of potential employees with advanced technical and leadership skills
who can add value to their organisations.

2. The UK High-Value Manufacturing Community will benefit as the CDT will:

- Develop the underpinning science and advanced-level knowledge base required by future high technology areas, where
there is high expectation of gross added value.
- Provide an enhanced route to exploitation, by covering the full spectrum of technology readiness levels.
- Ensure dissemination of knowledge to the sector, through student-led SME consultancy projects, the National Student
Conference in Metallic Materials and industry events.

3. The wider UK economy will benefit as the CDT will:

- Promote materials science and engineering and encourage future generations to enter the field, through outreach
activities developed by the students that will increase public awareness of the discipline and its contribution to modern
life, and highlight its importance to future innovation and technologies.
- Develop and exploit new technologies and products which will help to maintain a competitive UK advanced
manufacturing sector, ensure an internationally competitive and balanced UK economy for future generations and
contribute to technical challenges in key societal issues such as energy and sustainability.

References:
1. Materials UK Structural Materials Report 2009
2. EPSRC Materials International Review 2008
3. EPSRC Materially Better Call 2013
4. The state of engineering, Engineering UK 2017
5. Vision 2030: The UK Metals Industry's New Strategic Approach, Metals Forum