Hydriding behaviour of Zircaloy-4/stainless steel type 304 diffusion couples

The behaviour of diffusion-bonded Zircaloy-4/stainless steel junctions under thermal and electrolytic hydriding conditions was studied. The results showed that these junctions have the ability to absorb large amounts of hydrogen. The diffusion zone and most of the Zircaloy side, which was enriched with Ni, were transformed to complex hydrides. In the diffusion zone, the α-Zr phase and an intermetallic compound (phase X) formed hydrides after relatively short electrolytic hydriding times. Cr2Zr, found in the diffusion zone, showed a large hydrogen solid solution behaviour with an increase of 18.4% in the lattice volume. A martensitic transformation in austenitic stainless steel was also observed. The detrimental effect of Ni in Zircaloy was interpreted in terms of the role played by Zr-Ni intermetallic compounds. (Auth.)