In-situ studies of strain accommodation in MAX phase materials for advanced nuclear energy

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MAX phases are 2D-layered hexagonal carbides or nitrides that can exhibit very high mechanical damage tolerance at high temperatures. In common with ceramics, they are significantly less activated than metals by fast neutron irradiation. Hence they have potential applications in structural applications for advanced nuclear fission. However, the structure/property relationships and mechanisms of damage accumulation in MAX phases need to be better understood for microstructure-based modelling to support the design and development of materials and engineering components. Strain mapping by both image analysis and diffraction has revolutionized studies of deformation in structural materials. Together, they can provide excellent knowledge of both the elastic and plastic strain states within complex structures, which are internally "strain gauged" in three-dimensions with high spatial resolution. Image correlation tools applied to tomographs can measure three-dimensional deformation and total strain states with high precision. Diffraction analysis to measure elastic strains within bulk materials is also routine with neutrons and also on high energy synchrotron X-ray beam-lines. The project aims to use X-ray and neutron diffraction and imaging to map, in situ and in 3D, both the total and elastic strains under load and at elevated temperature, and thereby perform novel studies of the mechanisms of strain accommodation in bulk MAX phase materials for nuclear energy, with emphasis on the effects of strain history, microstructure texture and material heterogeneity, in order to improve material reliability and performance. The objectives of the project are to study, in particular, the differences between phase pure and commercial purity MAX phase materials from the TiAlC system, including the application of high resolution electron backscatter diffraction (EBSD) to study the transfer of strain between grains and phases, which may be affected by the texture that is introduced during processing. This project interacts closely with a parallel project, starting at the same time, that is conducting studies of strain accommodation in MAX phase materials for advanced nuclear energy at the microscale, using high temperature nano-indentation and high resolution microscopy. This project collaborates with SCK-CEN (Belgium) who are developing MAX phases for nuclear applications in conjunction with the European Energy Research Alliance Joint Programme in Nuclear Materials that aims to develop materials for next generation sustainable nuclear energy. The project also connects with the H2020 Il Trovatore programme on Innovative cladding materials for advanced accident-tolerant energy systems, in which standard mechanical testing (including studies of irradiated materials) are being conducted by SCK-CEN, together with electron-microscopy microstructure characterisation by EBSD and Transmission electron microscopy. This project falls within the EPSRC Energy Research Theme (Nuclear Power).