High Temperature Strain accommodation in MAX phase materials for advanced nuclear energy

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.

MAX phase materials owe their unique properties to the tendency for crystal deformation by kink formation. This is a little understood phenomenon, but is similar to that observed in graphite. The influence of temperature and irradiation on kink formation is not understood, but theoretical studies have shown a strong link between the chemistry of the Max phase and the cleavage stress, which may affect the brittle/ductile transition. Better understanding of this fundamnetal mechanism would lead to the design of MAX phase materials with improved properties.

The objectives of the project are to use high resolution electron backscatter diffraction to map grain orientations and to study the localisation of strain in phase pure MAX phase alloys from the TiAlC, ZrAlC and CrAlC systems, tested at elevated temperature. The effects of ion-irradiation on the deformation mechanisms will also be investigated. In particular, novel high temperature nano-indentation investigations will be performed, in grains of selected orientations, to study how plastic strain is accommodated within the crystal structure as a function of temperature. Sectioning of the deformation zone beneath nano-indentation will be done using focussed ion-beam milling, to enable high resolution transmission microscopy and transmission Kikuchi diffraction analysis. The studies aim, in particular, to understand how irradiation affects the mechanisms of deformation, as this will have impact on the transition between ductile and brittle behaviour at the macroscale. This project interacts closely with a parallel project, starting at the same time, that is conducting in situ studies of strain accommodation in bulk MAX phase materials for advanced nuclear energy using X-ray and neutron scattering and imaging.

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 whicb mechanical testing (including studies of irradiated materials) is being conducted by SCK-CEN, together with electron-microscopy microstructure characterisation by EBSD, Transmission electron microscopy and ion-irradiation of MAX phase materials by Manchester University (Prof. P. Frankel) and Huddersfield University (Prof. K. Lambrinou).

This project falls within the EPSRC Energy Research Theme (Nuclear Power)