An analysis of small clusters formed in thermally aged and irradiated FeCu and FeCuNi model alloys

The pressure vessel of a pressurized water reactor, containing residual levels of copper, can be embrittled by the radiation enhanced formation of copper-rich clusters during operation at 290 degrees C. It is important to study the effect of irradiation and materials variables, such as nickel content on the nature and development of these clusters to increase understanding of the underlying mechanisms and to improve the theoretical models used to predict embrittlement trends. To achieve this, it is necessary to employ a variety of analytical techniques and to investigate simple model alloys, as well as complex, low alloy steels. In this paper, atom-probe field-ion microscopy, small-angle neutron scattering and transmission electron microscopy have been used to study the precipitation in iron copper (FeCu) and iron-copper-nickel (FeCuNi) alloys thermally aged for up to 10 h at 55 degrees C, or irradiated to doses up to 6.95 x 1019 n · cm-2 (E > 1 MeV) at 290 degrees C. The results on precipitate composition, number density, size distribution, and matrix composition obtained using the three techniques are compared and contrasted. In general, their agreement is good