Ponente
Descripción
Dissimilar welds between austenitic stainless steels and EUROFER97 are unavoidable in the DEMO Oriented Neutron Source (DONES) Target Assembly (TA), particularly in the Backplate (BP), where 316L/316Ti piping joins EUROFER97 structural components exposed to extreme neutron flux, lithium velocity and thermal gradients that drive BP lifetime. This work assesses thin TIG (GTAW) butt welds in 1G configuration without filler on 2 mm plates, establishing a unified framework for the structural integrity and liquid lithium compatibility of BP relevant joints.
A 316L–316L reference campaign validated the welding configuration and identified the optimal current window balancing penetration, internal defects and heat affected zone (HAZ) extension. Radiographic inspection showed evolution from lack of fusion at low current (32-34 A) to porosity at high current (45-55 A), with 38-42 A providing the best continuity/porosity compromise. Optical microscopy, SEM and EBSD confirmed austenitic solidification with minor delta ferrite and the equiaxed-to-directionally solidified transition, while room temperature tensile tests and Vickers hardness profiling (200 gf) established the mechanical baseline.
Dissimilar 316L–EUROFER97 and 316Ti–EUROFER97 BP representative coupons required higher current (≈65 A) for stable fusion due to EUROFER's distinct thermal properties. Metallographic examination and hardness traverses revealed pronounced microstructural/hardness gradients at ferritic–austenitic interfaces, emphasizing robust preparation/etching needs.
The assessment matrix includes radiographic inspection, EBSD phase/texture mapping across interfaces, and tensile testing for joint level strength, ductility and fracture location. Corrosion performance is evaluated through dedicated liquid lithium exposures (ELIOS-CIEMAT) in sealed AISI 316L containers with high purity Li, assembled in inert atmosphere glovebox, pressurized to 5 bar Ar, heated up to 350 °C, and operated under controlled T/P with real time SCADA monitoring. As welded and Li exposed specimens undergo identical microstructural (optical/SEM/EBSD) and mechanical (tensile/hardness) characterization, enabling direct comparison and quantitative appraisal of DONES TA Backplate dissimilar TIG weld integrity under structural and lithium breeder conditions.