Cross-sectional nano-indentation of ion-irradiated steels: Finite element simulations based on the strain-gradient crystal plasticity theory

Abstract

In this work, the cross-sectional nano-indentation of ion-irradiated steels is simulated by the crystal plasticity finite element method. Two dominant features, including the non-uniform irradiation hardening and indentation size effect, are characterized by considering the influence of inhomogeneously distributed irradiation defects and geometrically necessary dislocations within the framework of strain-gradient crystal plasticity theory. The theoretical model is applied for ion-irradiated 304 stainless steel. Both the fitted and predicted macroscopic mechanical responses are compared with experimental data under different irradiation conditions, which include the force-depth (F−h) and hardness-depth (H−h) relationships under surface nano-indentation, and hardness as a function of the distance from the irradiated sample surface (H−x) under cross-sectional nano-indentation. A good agreement is achieved that can validate the rationality and accuracy of the proposed model. Furthermore, the three-dimensional relationship of H−x−h is analyzed under cross-sectional nano-indentation, which indicates that the hardness of ion-irradiated materials depends on both the distribution of defect density in the irradiated layer and indentation position with respect to the irradiated and indented sample surface. Moreover, the evolution of different hardening mechanisms is addressed in details, which can help obtain a sophisticated comprehension of the fundamental mechanisms that result in irradiation hardening and indentation size effect.