Radiation induced phase separation in Fe-based copper containing alloys

Investigations on the radiation generated fast precipitation from supersaturated metastable Fe(Cu) solutions and some related real and laboratory steels, subjected to fast neutron bombardment in the materials test reactor SAPHIR at PSI, are reviewed. The irradiations were performed at 290C at a special facility under controlled thermal and radiation conditions up to a few different fluences. For the detection of the precipitated particles various experimental techniques, like small angle and diffuse elastic neutron scattering, positron annihilation and the variation of internal friction and microhardness were used. In contrast to those generated by heat treatments above ∝ 450C, the precipitates have mean radii as small as 8-14 A, their size goes to saturation with increasing fluence. Intermediate annealing between subsequent irradiation periods is seen to lead to a bimodal size distribution. Evidence on a strong vacancy content of the radiation induced precipitates is obtained by both positron and SANS results. A first application of muon spin rotation spectroscopy on neutron irradiated iron and on annealed Fe(Cu) samples shows the sensitivity of the method to both vacancy-like defects and to the Cu-depletion of the solvent matrix. Preliminary SANS data on irradiated laboratory steels with varying contents of Cu, Ni and P indicate, besides a strong correlation of precipitated volume fraction with microhardness, a complex local magnetic structure of the precipitated phase