Model for the spherical indentation stress-strain relationships of ion-irradiated materials

In this work, a mechanistic model is proposed to characterize the spherical indentation stress-strain (ISS) relationships of ion-irradiated materials. Three fundamental deformation mechanisms are accounted for by the developed model, including the indentation size ef- fect (ISE) ascribed to geometrically necessary dislocations (GNDs), irradiation hardening determined by irradiation-induced defects and strain softening affected by the removal of defects and unirradiated substrate. The contribution of elastic deformation is involved to model the ISE of spherical indentation, ignoring which can result in the overestimation of the indentation stress at a small indentation strain. In addition, the removal of irradiation- induced defects by outspreading plastic deformation and softening effect induced by the unirradiated substrate are simultaneously considered to account for the strain softening phenomenon with irradiation effect, which is well known in conventional tensile tests af- ter the yield point. A good agreement is observed by comparing our model results with the experimental data of unirradiated materials (iridium, nickel, aluminum and copper) and ion-irradiated Fe-12Cr alloy. The proposed model offers a promising way to qualita- tively compare the ISS relationships of ion-irradiated materials and uniaxial stress-strain curves of neutron-irradiated materials.