Dose dependence of irradiation hardening of neutron irradiated vanadium alloys by using temperature control rig in JMTR

TEM observation and tensile test were examined for vanadium alloys irradiated in a temperature control rig in JMTR at 290 °C with damage level ranged from 0.003 to 0.06 dpa. With the increase of the neutron dose, irradiation hardening could be observed in all the vanadium alloys except for the V-5Nb alloy. In the case of pure vanadium, the relationship between irradiation hardening and neutron dose was described as Δσ  ∝ (ϕt)0.35-0.53. For V-5Cr alloy and V-4Cr-4Ti-0.1Si alloy, the dose dependence on irradiation hardening increase was shown as Δσ ∝ (ϕt)0.8 and Δσ ∝ (ϕt)0.8-1.0, respectively. From the TEM observation, the hardening source of radiation-induced defects was mainly determined to be dislocation loops for pure vanadium, loops with voids for V-5Cr and, loops and {100} precipitates for V-4Cr-4Ti-0.1Si and V-3Fe-4Ti-0.1Si alloys. From the strain rate dependence of 8% stress for V-4Cr-4Ti-0.1Si alloys tested at RT, the strain rate sensitivity, m = 1/σ*(dσ/dln(dε/dt)) shows positive. Therefore, the dynamic interaction between interstitial impurities and dislocation is not strong in V-4Cr-4Ti alloys in the temperature range from RT to 290 °C. A discrepancy of deformation mode of irradiated V-4Cr-4Ti-0.1Si alloys with 0.068 dpa could be seen when the charpy impact test indicated the brittle behavior and the tensile test indicated the ductile behavior at room temperature. It can be explained by the difference of strain rate for the value of yield stress between tensile test and charpy test and the critical fracture stress.