On the role of Ni, Si and P on the microstructural evolution of FeCr alloys under irradiation

In this experimental work the behaviour of Ni, Si and P, typical impurities or low alloying elements in ferritic/martensitic nuclear steels, with increasing irradiation dose was investigated in model FeCrX (X = Ni, Si, P, NiSiP) alloys using atom-probe 3D maps. These elements are known to increase the embrittlement and the hardening of steels by segregating at internal surfaces and creating solute-rich clusters at 300°C. This study is focused on the analysis of the clusters and the influence of every chemical specie in their formation. The model alloys have been irradiated with 5 MeV Fe2+ ions up to 0.1 and 0.5 dpa at 300°C and the 3D atom maps have been analysed using statistical tools and iso-concentration algorithms. P is proven to be the fastest diffuser whereas Ni and Si are slower. The three species segregate together strengthening the idea that they are decorating stable defect clusters by dumbbell or vacancy dragging. And no apparent influence on the clustering of every element over the others is observed up to 0.1dpa, suggesting the absence of synergistic effect between these species.