Effects of Ion Irradiation on Laser Welded V-4Cr-4Ti Alloy

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High purity V-4Cr-4Ti alloy, fabricated by National Institute for Fusion Science (NIFS), was used for this study. The samples were annealed at 1273K for 2 hours and bead-on-plate welds were performed using high purity argon gas. A 2.4MeV copper ion irradiation was carried out with the tandem accelerator at Kyushu University. The TEM samples were sliced from the welded materials and irradiated at 573K and 873K up to the dose of 12 dpa. The microstructure before irradiation showed that relatively large Ti(C, O, N) precipitates which were commonly observed in V-4Cr-4Ti alloy disappeared in the center of weld metal. After the ion irradiation at 873K, fine titanium oxides with {100} habit plane were detected at the dose of 0.75 dpa. Lower number density of the oxides was observed in the base metal after the same irradiation conditions. This means that the contribution of oxygen atoms, which dissolved from the large precipitates during the laser welding, is essential to the microstructural evolution of welded V-4Cr-4Ti alloys.