A statistical mechanics-based irradiation creep constitutive model for the Ni-based superalloy used in molten salt reactors

We proposed a new constitutive model for steady-state irradiation creep based on nonequilibrium statistical mechanics. The creep dynamics is understood in effective potential-energy landscapes and the derived constitutive equation contains three physical parameters that are only dependent on material microstructure and irradiation damages but independent of either temperature or stress. The model was firstly validated by our thermal creep experiments of the Ni-16Mo-7Cr-based superalloy in a range of 650-800°C and 120-360 MPa as well as by other reported Al, Fe and Ni-based alloys. The model was further applied to predict creep rates and lifetime under neutron irradiation and the verifications were made by comparisons with available in-reactor creep data of the Ni-based superalloy. For the purpose of engineering safety assessments on the material, the irradiation creep rupture time up to 10 5 hours was predicted by our approach for the Ni-based superalloy in a wide range of 600-800°C, 100-350 MPa and thermal neutron fluences of 1.3×10 19 -1.5×10 21 N/cm 2 , and the nonlinear behaviors of the creep lifetime reduction factor were discovered for the first time. The creep model may find its vast applications in rapidly evaluating long-term thermal and irradiation creep properties of other alloys materials in practical engineering usages.