Deuterium permeation performance of V4Cr4Ti/RAFM steel joint with in-situ formed carbide interlayer during diffusion bonding

Vanadium alloy (V4Cr4Ti) is a structural material used in future fusion reactors owing to its inherent advantages of high-temperature strength and neutron irradiation resistance. Oxygen pickup and high hydrogen isotope permeability are the two major concerns for their application in various types of blankets. To solve these issues, a bimetallic joint was designed with a CLF-1 layer of reduced-activation ferritic/martensitic (RAFM) steel to resist corrosion and a CLF-1/V4Cr4Ti bonding interface to suppress hydrogen isotope permeation. Samples were prepared from joints bonded via solid-state diffusion under hot isostatic pressing (HIP). Deuterium (D) gas permeation tests were performed at various temperatures in the range 400–600 °C at 100 kPa. After deuterium permeation tests, the thermal desorption spectra (TDS) of the samples were analyzed. And the permeation behavior of deuterium atom across the joints was schematically discussed. The results showed that bonding with steel could be an effective solution for resisting hydrogen isotope permeation through the V4Cr4Ti alloy. Thermal desorption spectrum (TDS) analysis of the tested samples revealed a desorption peak temperature equivalent to that of TiC. The formation of a 1 µm-wide B2 ordered α`- [Fe, (V, Ti)] phase layer, together with a large number of dispersed carbides around the interface, played a significant role in the deuterium permeation resistance. In addition, microstructural changes in the steel base material after the 900 °C bonding process were beneficial for suppressing deuterium diffusion.