J. Phys. IV France
Volume 12, Numéro 8, September 2002
Page(s) 85 - 92

J. Phys. IV France
12 (2002) Pr8-85
DOI: 10.1051/jp4:20020325

Consequences of calcium and sulphur spallation product recoils in 9Cr-1Mo steel: Simulation by ion implantation

G. Amiri1, M.-O. Ruault1, J. Henry2, H. Bernas1, E. Cadel3 and P. Pareige3

1  CSNSM, IN2P3-CNRS, UMR 8609, bâtiment 108, Université Paris-Sud, 91405 Orsay cedex, France
2  CEA-SRMA, Centre d'Etudes de Saclay, 91191 Gif-sur-Yvette cedex, France
3  Groupe de Physique des Matériaux, UMR 6634, Faculté des Sciences, Université de Rouen, 76821 Mont-Saint-Aignan, France

In the presently envisaged Accelerator Driven System (ADS), the spallation source window material (containing the molten Pb-Bi target) will be a steel containing 9 wt.% chromium (EM10 and T91). The material will be subjected to both high damage rates (some 100 dpa per year at full power) and to the production of significant concentrations (typically 1000 appm) of a large spectrum of impurity elements produced by spallation of the window constituents. We have experimentally simulated the effects due to two of the more deleterious spallation products - Ca and S - by ion implantation at (or near) the expected ADS window operating temperature ( $500^\circ$C). Transmission Electron Microscopy (TEM) observations were carried out either after the high temperature implantations (ex-situ) or during the latter (in situ) using the CSNSM on-line TEM coupled to an ion implanter. Two compromises were made (besides the limitation in the number of implanted species) which differ from the true ADS operating conditions: (i) for practical reasons, the implantation beam flux was typically a factor 10 2 higher than the expected spallation product generation rate; (ii) in order to maximize the possibility of observing precipitation of these presumably insoluble elements, Ca and S implant concentrations reached 1-2 at.%. The displacement levels corresponding to such implantations were 20-25 dpa. As expected, TEM revealed that the defect structure evolved from dislocation loops at low fluence to the formation of a dislocation network as the fluence was increased; this did not depend on the nature of the implanted element. No other significant changes occurred in the steel (including in the size and composition of its inclusions): no new phases were detected in the TEM experiments. On the other hand, small ( < 2 nm) Ca precipitates were indeed detected in 3D atom probe measurements. Their small size accounts for our TEM results.

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