Brazing Tungsten/Tantalum/RAFM Steel Joint for DEMO by Fully Reduced Activation Brazing Alloy 48Ti-48Zr-4Be

To create a DEMO reactor, it is necessary to develop high-quality technology to join tungsten with reduced-activation ferritic-martensitic (RAFM) steel (Rusfer, Eurofer, CLF-1, etc.). Difficulties arise in their direct connection due to the large difference in the coefficient of thermal expansion (CTE). To suppress the difference of CTE, intermediate interlayers are usually used, such as vanadium or tantalum, and brazing is a prospective technology to conduct the joining. The vast majority of works represent copper- or nickel-based brazing alloys, but their applicability is under significant discussion due to their activation properties. That is why, in this work, fully reduced activation 48Ti-48Zr-4Be wt.% brazing alloy was used. The following joint was made: Rusfer steel/48Ti-48Zr-4Be/Ta/48Ti-48Zr-4Be/W. The brazing was successfully carried out under a mode providing thermal heat treatment of Rusfer. Through EDS and EBSD analysis, the microstructure of the joint was determined. Shear strength of the as-joined composition was measured as 127 +/- 20 MPa. The joint endured 200 thermocycles in the temperature range between 300-600 degrees C, but the fillet regions degraded.

Automated summary

In order to connect tungsten with reduced-activation ferritic-martensitic steel in a DEMO reactor, high-quality technology using 48Ti-48Zr-4Be wt.% brazing alloy with vanadium or tantalum intermediate layers was developed. The shear strength of the joint was successfully measured, but degradation was observed in the fillet regions after 200 thermocycles in the temperature range of 300-600 degrees C.