No abstract

Samples of FeCu. FeCuMn, FeCuNi, and FeCuCr alloys containing 1.5 wt% of each solute have been electron irradiated around 2 9 0 T or thermally aged Y SOOT for various times. It is known that such treatments induce Cu precipitation; the Cu depletion of the mahix is measured by the resistivity decrease of the samples. The clystallographic environment of the solute atoms in the irradiated or aged samples has been studied by %AS (x-ray absorption spemoscopy).The data show that Cr, Mn, and Ni atoms mainly remain in BCC solid solution during the CO precipitation. The first Cu precipitates are found to be of BCC structure, i.e. coherent with the matrix. At the longest ageing times, they have become of Fa' smcture. In the electronirradiated samples, the data show that, up to a Ruence of5 C cm-', most of the Cu precipitates (> 80%) are still of Bn: structure.The fraction of BCC precipitates has been estimated from both Lhe x-ray-absorption near-edge structure (XANES) and extended x-ray-absorption fine-structure (EXAFS) data It appears that, for both FeCu and FeCuMn samples, similarly aged, the FCC fraction is larger in cold-rolled samples than in pre-annealed and quenched ones.The results obtained are consistent. in the FeCu case, with a simple linear correspondence between Ruence and time, 1 C cm-' at 3 0 0 T being equivalent to -IO h at S W T . The CO precipitation is found to be accelerated, at least in its first stages, by the presence of Mn in thc alloy.