Improved testing for thermal cycling of materials in water vapour environments

Cranfield University researchers have used Royce Institute Industrial Collaboration Project funding to upgrade their facilities in order to widen their testing capabilities for hydrogen engine components.

The use of hydrogen as fuel for combustion engines is one of the main strategies that has been proposed for the decarbonisation of the transport section, particularly in applications such as heavy goods vehicles and long-haul flights.

Whilst the generation of large quantities of H₂0 instead of CO₂ is less harmful for the environment, it poses a serious materials challenge for engine components as they will experience larger volumes of water vapour than conventional engines and potentially higher temperatures due to the more energetic combustion.

In order to fully understand the material degradation mechanisms involved to support future engine design, further research must be done on the combined effects of temperature, water vapour levels and thermal cycling on component materials as well as surface engineering solutions to protect them. In order to address these challenges, Cranfield University researchers have been working in collaboration with Zircotec Ltd, Rolls Royce and Imperial College London on a ICP project funded by the Royce Institute. 

Up until now thermal cycling has not been well studied due to the lack of facilities able to achieve representative conditions of the working environment. This project involved adapting the current Royce Institute testing facilities at Cranfield to include water vapour thermal cycling up to 1500°C and 100% effective water vapour. 

Relevant engine materials were then provided by Rolls Royce and Zircotec Ltd and were tested in the upgraded facilities under different operational conditions, providing useful and relevant data for these companies. This data will provide knowledge to aid the design for enhanced protection and extended lifespan of critical engine components. 

Zircotec Ltd provided samples of Stainless Steel 304, a representative engine construction material, with and without Zircotec’s protective surface engineering solutions (bondcoat and Thermal Barrier Coatings (TBC) deposited by Air Plasma Spray) for testing.  The samples were coated on one side with one of three different TBC systems, which allowed for evaluation of both exposed and protected substrate.

Following the testing, the samples were characterised by a combination of scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX) and other characterisation techniques to understand the behaviour of the specimens, identify their mechanisms of failure, and evaluate the severity of oxidation/corrosion.

Happily, this characterisation showed that the coatings that were used were able to withstand a high number of thermal cycles within extremely high levels of water vapour. The research showed that the coatings used showed robustness to typical conditions within hydrogen engines and acted as successful barriers against steam corrosion, offering promising results for the design of hydrogen engine components.

The upgraded facilities within Cranfield now also have the ability to provide UK industry and academia (through the Royce Institute Access Scheme) with the tools to evaluate lifing of current materials and to design next-generation materials for future propulsion systems.

For information on Cranfield facilities and other potential projects, please contact Luis Isern Arom.

For information on our research with Zircotec and their coatings technology, please contact Dominic Graham.