Irradiation creep induced stress relaxation of Inconel 718

Torsional creep tests were conducted on Inconel 718 specimens under 17 MeV proton irradiation at 300°C for doses up to ∼0.08 dpa. The stress dependence of the irradiation creep rate was measured by increasing the maximum applied shear stress from 150 up to 450 MPa. The experimental results show that the stress dependence of the irradiation creep rate is linear in the whole stress range applied. The irradiation creep constant κ=1.2×10−11 (dpa−1 Pa−1) at 300°C. The calculated creep induced stress relaxation amounts to ∼10% after 0.1 dpa. The results are discussed in relation to the operating condition of an ITER-like machine, where Inconel 718 bolts are used to mechanically attach the shielding blanket to the back plate.