Abstract
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 creating solute-rich clusters at 300 °C. This study is focused on the analysis of these 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.
Highlights
Comprehension of low-temperature embrittlement in irradiated ferritic/martensitic steels under irradiation is critical in order to push the operation temperature windows for future Gen IV and fusion reactor components designs
Features: (i) dislocation loops detected by transmission electron microscopy (TEM) [4], (ii) solute-rich clusters (SRCs) observed by atom probe tomography (APT) and mainly enriched with Ni, Si, P and Cr [5,6] and (iii) Cr-rich clusters detected by APT and small angle neutron scattering (SANS) [5e8] which were identified as a0 precipitates
The solute distributions obtained from the APT volumes are shown in Fig. 2 and Fig. 3
Summary
Comprehension of low-temperature embrittlement in irradiated ferritic/martensitic steels under irradiation is critical in order to push the operation temperature windows for future Gen IV and fusion reactor components designs. In former works, hardening has been consistently explained in neutron irradiated model alloys whose purity was at an industrial level [1e3]. These FeCr model alloys, which had Cr concentrations ranging from 2.5 to 12 w%, contained some impurities of Ni, Si and P. In these alloys, the increase in yield strength is linked to the presence of three reported types of small features: (i) dislocation loops detected by transmission electron microscopy (TEM) [4], (ii) solute-rich clusters (SRCs) observed by atom probe tomography (APT) and mainly enriched with Ni, Si, P and Cr [5,6] and (iii) Cr-rich clusters detected by APT and small angle neutron scattering (SANS) [5e8] which were identified as a0 precipitates. The SRCs are systematically appearing in FeCr model alloys containing some Ni, Si or P impurities [5,6,9e12]
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