Nanohardening features in ion and neutron irradiated EUROFER97 and model alloys investigated with atom probe tomography

Among other effects, neutron irradiation hardens ferritic/martensitic (F/M) nuclear steels; this hardening is suspected to be due to the formation of dislocation loops, alpha' phase and solute-rich clusters (SRCs). In neutron irradiated FeCr model alloys the SRCs which are made of unavoidable impurities such as P are likely to be the main contributors to the yield strength increase, together with the presence of alpha' precipitates, if any [1,2]. Ion irradiation is an extended tool used to investigate the creation and evolution of radiation damage. Since the experiments are fast they offer the possibility to tune the parameters to design model-oriented experiments. Their use is also oriented to reproduce the effects of neutrons for nuclear applications. However, the characteristics of the nano-sized features (solute concentration, density, size and size distribution) are difficult to reproduce using ions with respect to neutrons, since the increase of the sink strength due to injecte d inters titials [3,4] and the high values of damage rate [5] influence defect production and evolution.
Atom probe tomography (APT) is used in the present work to investigate the hardening nanofeatures in irradiated materials. First, an Fe14CrNiSiP model alloy has been irradiated with both Fe+ ions and neutrons up to a dose of 0.1 dpa at 300°C. At such low doses some features, such as SRCs or Cr-rich regions, are formed, thus a direct comparison can be made to highlight differences and commonalities between the two kinds of irradiation; these results can also be used for the development of models. Second, a similar investigation has been made on neutron irradiated EUROFER97 up to 15 dpa at 300°C. The presence of radiation induced segregation (RIS) and radiation enhanced features can be correlated to the model alloy providing some insights on the nature of the hardening in F/M steels.