Recovery of hardness, impact properties and microstructure of neutron-irradiated weld joint of a fusion candidate vanadium alloy

Abstract

Weld samples of fusion reactor vanadium alloy (NIFS-HEAT-2) were neutron-irradiated at 563 K up to 4.5 × 1023 neutrons/m 2 (0.08 dpa). The recovery of irradiation hardening, degradation of impact properties, and damage structures in the weld metal were investigated after post-irradiation isothermal annealing at temperatures between 673 and 1073 K. Irradiation hardening and the decrease in impact absorbed energy at 77 K were larger for the weld metal than for the base metal. Recovery of the hardening by post-irradiation annealing was coincident with recovery of the impact absorbed energy in both the weld metal and the base metal. Recovery of the mechanical properties required post-irradiation annealing at 1073 K for 1 h for the weld metal, which was 100 to 200 K higher than that for the base metal. The dislocation loops introduced by the neutron irradiation are likely to account for the hardening. The dislocation loops were observed even after annealing at 973 K in the weld metal, whereas they disappeared in the base metal. The characteristics of the radiation defects in the weld metal and the mechanisms for irradiation hardening and embrittlement are discussed. © 2005 The Japan Institute of Metals.