Made for demanding environments

Materials World magazine
,
1 Feb 2018

Developing materials that can withstand the harsh environments they are used in remains a significant challenge. The UK’s Henry Royce Institute, a group of universities and organisations, aims to change this, as Michael Preuss and Freyja Peters* explain.

It can be a tough life for materials. They are subject to demanding environments, including in oil pipelines, which are at risk of material degradation and failure from both sweet (CO2) and sour (H2S) corrosion, in tandem with the environmental effects of, for example, deep-sea conditions.

Materials used in the process of nuclear power generation, such as pressure vessels and fuel cladding, need to be able to operate within reactors with minimal failure risk and without the need for premature replacement, requiring in-depth understanding of the behaviour of materials in an active environment. 

In the aerospace sector, gas turbine engines are subjected to extremely high temperatures beyond that which the turbine blades themselves – made from nickel-base superalloys – can withstand, so these must be coated with insulating thermal barrier coatings (TBCs). 

While many systems can and do cope, optimising their performance is critical in terms of increasing safety, extending component life and reducing costs. TBCs have demonstrably increased turbine engine operational temperatures, but there remains scope for further development to improve engine performance and efficiency. 

Meeting this challenge requires plenty of hard work between industry and manufacturers. Here is where the Materials for Demanding Environments concept, or M4DE, as it is known, comes in.

The what if scenarios

M4DE, which is part of the Henry Royce Institute, the UK’s national centre for advanced materials research, is led by the Royce hub at the University of Manchester, with partners at the universities of Sheffield, Liverpool, Leeds, Oxford, Cambridge and Imperial College London, as well as the National Nuclear Laboratory and the Culham Centre for Fusion Energy. The group is working to define and address the key challenges presented by demanding environments. This includes materials systems for aeroengine components, for deep-sea oil and gas transport and drilling, nuclear environments, high-temperature electrical systems, smart/responsive, impact-resistant and abrasion-resistant materials. 

The starting point was a series of questions around what is needed from materials enhancements. What if, for example, erosion-resistant coated oil piping with in-built sensors could be developed? What if turbine blade coatings were self-healing? What if nuclear fuel assemblies could withstand accidents for hours instead of minutes? 

From these questions, M4DE developed the three fundamental challenges that must be addressed. The development of materials systems that exceed the capability of advanced metals, or protect these, the expansion of testing and characterisation capabilities for the evaluation of structural materials in demanding environments as well as the improvement of fundamental understanding of degradation mechanisms.

There is a pertinent question to address, one that can be described as the missing step between research and manufacture and application. In essence, M4DE’s vision is to bridge the gap between the low technology readiness levels associated with academic research (TRL 0/1) and the higher levels associated with catapults.

A crucial aspect of developing new materials systems is to understand the relationship between manufacturing parameters and in-service performance. This cradle-to-grave approach will help in the transition from innovation to application, by creating a culture of confidence around the safety and efficacy that can be expected on implementation. 

Meeting the challenge

Royce’s investment in M4DE will focus on developing protective and smart coatings and hybrid material systems that will widen the space in which structural materials can be used. M4DE will also provide a platform to test structural materials in corrosive, high-pressure, high-temperature and other demanding environments. This, in combination with mechanical loading from low to very-high strain rates and in-situ characterisation capabilities for mechanistic understanding of material degradation, will help guide new material development. 

With M4DE, there’s an aim for the production, deposition and testing of coatings. Research has been identified as a critical area, with a number of industrial drivers behind it, and a key focus on coatings for components exposed to demanding environments.

Ongoing research includes the development of TBCs for aero-engine turbine blades – an important UK industrial sector – as well as ceramic coatings as environmental barrier protection for ceramic matrix composite blades, which have been identified to replace current super-alloy blades.

Coating technologies and ceramic matrix composites for nuclear applications are also part of the package, with research on coating of zirconium-based fuel cladding and the development of SiC fuel cladding. Using a range of techniques not only for producing different coating compositions, but also for applying them, this research seeks to enhance performance in normal operation and the unlikely event of an accident scenario. 

This will link closely to the Royce Nuclear Materials theme, which focuses on active material. The UK has recently received unique zirconium cladding samples irradiated in a test reactor, providing an opportunity for the country to be at the forefront of research to develop more efficient, accident-tolerant fuel cladding materials. 

There will also be a bespoke tribology suite, for the testing, analysis and development of coatings and surface treatments. Research will be geared towards enhanced high-temperature fretting in jet engines, erosion-corrosion resistant coatings for oil and gas, and improving valve seat surfaces for power generation.

Going hybrid

A hybrid multifunctional structural materials lab is being established to exploit the latest developments in multi-scale, multi-component manufacturing set-ups, such as freeze-casting and high-temperature sintering, and 3D printing to design and make hybrid materials. 

One fundamental part of this are filters for petrochemical plants made of hierarchical ceramic-based hybrids – all with the aim of improving filtration efficiency, durability and reducing costs. Other potential applications include sound-absorbing systems for gas turbine combustion chambers, water pumps and engines, high-temperature filters for molten metal filtration before casting, material systems for self-healing structural health monitoring for aerospace components, load-bearing bone implants and material systems for catalytic supports and new fire-retardant material systems for the construction industry. In addition, there could be a chance to look at the architectures of high thermal/electrical conductive non-oxide ceramic-based materials for propulsion, micro combustors and new brake systems. 

In terms of testing capability, Manchester is already home to the UK’s largest university-based autoclave facility and Royce investment could see this double in size, becoming the jewel in the crown of a comprehensive UK centre for high-temperature, high-pressure testing in a range of realistic demanding and harsh environments. 

This all feeds into understanding how corrosion, erosion, fatigue, environmentally assisted cracking (EAC), stress corrosion cracking (SCC) and hydrogen embrittlement, affect materials. The facility also includes H2S and CO2 testing labs, while another strand is looking at degradation mechanisms of reactor pressure vessel (RPV) steel-enabling life extensions of future reactors. 

M4DE for the future

The M4DE team is also looking at the development of equipment and techniques that will drive forward future research, mainly through work on an in-situ testing and degradation characterisation capability. This will eventually include a suite of SEM-based in-situ testing stations, to be used for imaging during mechanical loading in various environments.

To achieve this, academics and experimental officers are liaising with manufacturers on creating a micromechanics suite, which will allow researchers to undertake a range of loading experiments inside the microscope and record maps of strain localisation – often a major factor in the failure of high-performance alloys – by using high-resolution digital image correlation (HR-DIC). 

M4DE is also working with PhD students, particularly through the Engineering and Physical Sciences Research Council’s Centres for Doctoral Training, with one eye on the next generation of scientists and engineers who will implement these technologies.

Alongside this, there is investment in existing equipment, such as an O-RF Plasma Ion Source for NanoSIMS, and a proposed advanced mechanical-environmental testing suite, to be situated in Manchester’s X-Ray Imaging Facility. The latter would allow testing under tensile and compressive loads in humid and liquid environments at a range of temperatures from 5-650°C and at pressures up to 100 Bar. 

Ultimately, the ability to make new materials, with an emphasis on coatings and hybrids, will accelerate material systems development and their use in industry. 

It may indeed be a tough life, but research can make it just that bit more bearable.

Read more about the Royce Institute here: www.royce.ac.uk/about-us

*Michael Preuss is Professor of Metallurgy at the University of Manchester, UK. His research focuses on microstructure, mechanical properties and residual stresses in high-temperature materials for nuclear, aeroengine, and oil & gas applications. He is also Deputy Director of the University of Manchester’s Materials Performance Centre and the Nuclear Rolls-Royce University Technology Centre at Manchester.

Freyja Peters is Centre and Research Administrator at the University of Manchester’s Materials Performance Centre.