A Novel Transition Layer Structure for Integrating Tungsten and Reduced Activation Ferritic/ Martensitic Steel

To date, a feasible solution is yet to be found for the transition between the plasma facing components (PFCs) and structural materials of fusion reactors. A well-considered design is necessary for the joining of plasma facing component such as tungsten and structural components such as reduced activation ferritic martensitic steel (RAFM), so that issues like the formation of brittle intermetallic phases and the large difference in tungsten vs. RAFM coefficient of thermal expansion are mitigated while maintaining good thermal contact and acceptable mechanical strength and ductility. In this study, computational thermodynamics and diffusion kinetic modeling were leveraged to design the composition and configuration of five-layered transitional structure (RAFM-FeCrAl-VCrAl-VCrTi-W) with the goal to prevent formation of brittle intermetallic within the temperature range 620 ~1150 ºC for a prolonged period of time. To analyze the viability of the design and to show the proof of concept, spark plasma sintering (SPS) was used to produce this five-layered transition structure to gain an in-depth understanding of diffusion kinetics between the interlayers for different heat- treated states. With an iterative approach, these experimental results were utilized to refine the composition of each interlayer and validate thermodynamic and kinetic databases that were originally used to design the transition structure. Knowledge acquired on diffusion characteristics of elements from each interlayer will play a vital role in advanced manufacturing techniques, such as additive manufacturing, to produce complex structural parts for future fusion reactors.