Micromechanical testing of irradiated nuclear fusion materials

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Any future nuclear fusion power systems rely on the development of materials which can withstand some of the most extreme engineering environments. These include temperatures up to 1500oC, high fluxes of high energy neutrons and effects of gaseous elements produced by transmutation and implantation from the plasmas. Due to efforts to minimise the production of nuclear waste by such reactors the elements which may be used in structural components is limited and in many cases there is a lack of understanding of the basic deformation processes occur in ether pure materials or alloys and importantly how these are effected by temperature, radiation damage and gas content. Due to the long time periods required for neutron irradiation campaigns, plus the associated cost and difficulty of working with active materials there is a need to develop robust methods for the characterisation of irradiated materials on the microscale. There are two advantages to this. Firstly it allows the maximum data return from small volumes of neutron irradiated materials. Secondly it allows the use of heavy ion irradiation to mimic neutron damage. In this case while the damage is similar to that of neutrons and can be built up in much shorter time frames the damage is only over a few 10's of microns. This precludes the use of traditional mechanical testing methods. While the methods required for understanding micro-scale plastic deformation are well developed micro-fracture testing has lagged behind. This project will build upon the expertise in the MFFP and Micromechanics groups on high temperature frcature testing at the micro and nano-scale. Facilities include two high temperature nanoindenters (-50oC to 950oC), high temperature microhardness (RT to 1500oC) and dedicated FIB-SEM and FEG-SEM with EBSD as well as high performance modelling stations. Both nanoindentation, micro-compression and micro-bend experiments will be used to study elastic-plastic fracture in tungsten and tungsten alloys. Understanding brittle failure of these alloys is key for the safe design of critical fusion reactor components such as the divertor. Currently diverter designs assume tungsten as the plasma facing components. However there is minimal understanding (only two previous studies-both lacking full experimental details in the published form) on the effect of irradiation damage on the brittle to ductile transition temperature in tungsten.HR-EBSD and TKD will be used to study the dislocation deformation structures produced around the crack tips during testing and to inform crystal plasticity based finite element and discrete dislocation dynamics models. The new science will concern both the development of robust elastic-plastic fracture testing methodologies as well as a the fuller understanding of the underlying physics of deformation in tungsten and tungsten alloys both before and after heavy irradiation or gas implantation. The work will include collaboration with CCFE-UKAEA through the fusion CDT.EPSRC theme and research area is Energy