Effect of Li on mechanical and corrosion properties of electron beam welds of V–4Ti–4Cr alloy (NIFS-HEAT-2)

The 4 mm thick plate of V–4Ti–4Cr alloy (NIFS-HEAT-2) was bead-on-plate welded by electron beam (1.5 kW) under high vacuum atmosphere. The samples were placed in V–5Ti capsule subsequently filled by liquid Li (8 g) in glove box under high-purity He atmosphere in order to avoid contamination of Li by O and/or N. Static corrosion tests were carried out at 700 °C for 500 h utilizing vertical water cooling furnace placed in the same glove box. During the test, liquid Li contacted with recirculating helium which was continuously purified with respect to O (4–30 wppm). After the test, the samples were cleaned against adhered Li in 30%H2O2 at 5 °C in order to avoid hydrogenation of V-alloy. After the welding, the impact properties of the weld metal measured at 77 K remained high enough (9.5 J) while fracture mode was ductile in spite of the solid-solution hardening by O released from Ti–C,O,N precipitates during high temperature electron beam welding. In contrast, impact properties of weld metal degraded after exposure to liquid Li (2.2 J) and post welding heat treatment (1.8 J) both carried out at 973 K. Character of fracture mode also changed to brittle due to the re-precipitation assisted hardening caused by aging effect.