Preliminary study on Hot Isostatic Pressing diffusion bonding of Fe-Cr-Al and CLF-1 steel for preparation of tritium permeation barrier

In the internal cooling channel forming of the blanket component for fusion reactor, the combination of Fe-Cr-Al ferritic steel with RAFM steel (reduced activation ferritic/martensitic steel) can form alumina film and then be served as tritium permeation barrier (TPB), which can inhibit the penetration of tritium into structural materials. To realize reliable joining between the two materials, Hot Isostatic Pressing (HIP) diffusion bonding, which is considered as the most promising fabrication technique for blanket component was used. The microstructure and mechanical properties of the joints were analyzed, and the results showed that Fe-Cr-Al/CLF-1 steel interfaces generated some large-size AlN, and the interfacial microvoids are not totally eliminated. While adding Ni interlayer between Fe-Cr-Al/CLF-1 steel could significantly reduce the size of AlN and promote interfacial microvoids closure. Fine NiAl and Ni3Al phases, as the strengthening phases in Nickel-based superalloys, were formed due to atom interdiffusion across the interfaces. Fe-Cr-Al/Ni/CLF-1 joints exhibited average tensile strength of 636 and 529 MPa, and elongation rate of 3% and 15% when tested at 25 and 300 degrees C, respectively. Microhardness test demonstrated Fe-Cr-Al/Ni/CLF-1 steel joints could be enhanced by precipitation-hardening of NixAly phases. These preliminary studies have laid a foundation for the preparation of TPB in the cooling channel of blanket components.