Cr effect on radiation damage in high purity FeCr alloys
A. Bhattacharya1, E.Meslin1, J.Henry2, B.Décamps3, C.Pareige4, C.Genevois4 and
D.Brimbal1
1
CEA-Saclay, Service de Recherches de Métallurgie Physique, 91191 Gif-sur-Yvette.
CEA-Saclay, Service de Recherches de Métallurgie Appliquée, 91191 Gif-sur-Yvette.
3
CSNSM -Université d’Orsay, 91405 Orsay Campus.
4
Groupe de Physique des Matériaux - UMR-CNRS 6634, 76801 Saint Etienne du Rouvray.
2
Reduced activation high-chromium ferritic / martensitic steels are candidate materials for the
generation IV fission and fusion reactors [1-3]. To gain knowledge about their radiation
resistance in such environments, the first step is to study the Fe-Cr matrix of this material. For
that purpose and to understand ballistic damage by neutrons, self-ion irradiations, with and
without simultaneous He injection, were performed on a series of high purity Fe-Cr binary alloys
at 773 K. The presentation will be focused on two main effects of Cr on radiation damage
formation in high purity FeCr alloys.
1. Cr enrichment on the habit plane of dislocation loops
Transmission electron microscopy (TEM) analysis revealed "displacement fringe
contrast" inside the dislocation loops. This was attributed to the presence of chromium enriched
zones on their habit plane, which is a defect-free region for bcc Fe based alloys. A plausible
mechanism will be discussed to explain the phenomenon, whose first step would be the radiation
induced segregation (RIS) of chromium atoms on the dislocation loop core (Fig.1). Energy
dispersive X-ray spectroscopy in scanning TEM mode and atom probe tomography (APT) gave a
coherent quantitative estimate of the chromium concentration in these enriched areas. APT study
showed that the enrichment was heterogeneous on the loop plane. Upon in-situ annealing up to
900 K, the loops and the fringes disappeared completely, without leaving a secondary phase
particle, like carbide, at their position. Fringes were present till the loop disappeared.
2. Cr effect on void swelling
A series of high purity FeCr alloys containing between 0 and 14 wt.% Cr were irradiated with
2 MeV Fe ions and 2 MeV degraded He ions within the Jannus Saclay facility up to 128 dpa and
13 appmHe/dpa. After irradiation, voids/bubbles were formed in all the studied materials. Void
swelling was deduced from all the studied materials. The trends indicted a minima close to 5 wt.
% Cr and a maxima close to 10 wt.% Cr in agreement with the literature obtained in low-purity
FeCr alloys and FeCr-based steels irradiated with neutrons [4]. However, the amplitude of the
void swelling is lower (close to one order of magnitude less), suggesting that the temperature of
the peak swelling after ion irradiation would not be exactly 773K.
3. Conclusions
By performing self-ion irradiations on high purity Fe-Cr alloys at 773 K, the presence of
chromium enriched zones on the habit plane of the dislocation loops have been shown by
complementary experimental techniques: conventional TEM, APT and analytical STEM/EDS.
This is expected to be due to RIS of chromium close to the core of the loops. As the loop grows
under irradiation, the segregated areas are probably stabilized from re-dissolving by impurity
elements like carbon.
The void swelling as a function of the Cr content has been obtained in a series of ion
irradiated FeCr binaries up to a large dose of 136 dpa with He. It shows that in agreement with
the literature data on the subject, the void swelling present a minima close to 5 wt. % Cr and a
maxima close to 10 wt. % Cr.
Fig. 1: Experimental evidence of the Cr enrichment on dislocation loops by complementary experimental
techniques. A schematic description of the mechanism proposed is given also.
4. Acknowledgements
Experiments were carried out at JANNUS (Joint Accelerators for Nanoscience and Nuclear
Simulation), Saclay, France and supported by the French Network EMIR and by EFDA
(European Fusion Development Agreement). The authors are thankful to the French national
project METSA for providing access to the atom probe tomography at University of Rouen
(METSA12 B08). This work was supported by the joint program "CPR ODISSEE" funded by
AREVA, CEA, CNRS, EDF and Mécachrome under contract n°070551.
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