Revealing the interaction of residual strain – mechanical performance using in situ neutron diffraction at high temperature for similar and dissimilar Eurofer97 joints

Nuclear fusion is a potential source of electricity which can address the environmental problems posed by
fossil fuels. The UK’s Spherical Tokamak for Energy Production (STEP) has progressed to the second
stage, as of 2024, from the concept design to the engineering design. Eurofer97 steel is a primary structural
material for in-vessel components in fusion Tokamaks. Assembling and maintaining works are necessary
for the structural integrity of these in-vessel components in high-temperature working conditions. This
requires joining techniques, forming similar and dissimilar Eurofer97 joints and inducing immense residual
stress. The interaction of the residual strain and the heterogeneous microstructure degrades the
mechanical performance and reduces the lifetime of these critical components. To mitigate the detrimental
effects of residual strain within the Eurofer97 similar and dissimilar joints, research must be conducted to
reveal the fundamental understanding of (i) the origins of residual strain inherited from the joining process
and its interaction with the high temperature, and (ii) underpinning deformation mechanism associated with
the residual strain at high temperature. The results obtained from the current study will enhance the design
protocols and structural integrity assessment of the EU DEMO and UK STEP (Spherical Tokamak for
Energy Production) fusion power plants.