Effect of Si–Ni–P on the emergence of dislocations loops in Fe–9Cr matrix under neutron irradiation: TEM study and OKMC modelling

Abstract

The expected degradation of mechanical properties of structural materials under irradiation (i.e. “in operation”) in nuclear components represents a significant challenge for the design to account the impact of long-term irradiation effects. Therefore, a development of scientific and engineering expertise to understand and possibly control the severe impact of harsh neutron irradiation on materials is one of the tasks in the current material’s research agenda. As it is well known from long-standing experience with fission systems, radiation embrittlement is caused by nano-scale features that obstruct plasticity mediated by dislocations. The present contribution highlights recent research and development efforts addressed towards the assessment of the interrelation between nano-structural features and hardening induced by neutron irradiation in fusion structural high-Cr ferritic/martensitic steels.In this work, the impact of doping by three chemical elements (nickel, silicon and phosphorus) on the microstructural evolution under neutron irradiation at 300 °C and 450 °C is studied experimentally as well as by computer simulations. The evolution of microstructure is assessed by transmission electron microscopy and object kinetic Monte Carlo simulations. The latter method utilizes a new approach enabling to follow both nano-scale irradiation defects and micro-segregation zones causing the formation of solute rich clusters, detectable by atom probe tomography. The results of the present work clearly point out that Ni–Si segregation alters the spatial and size distribution of dislocations loops already at as low dose as 0.1 dpa. The physical mechanisms behind the impact of minor alloying elements are discussed.