In situ small-angle neutron scattering study of the early stages of precipitation in Fe-25at% Co-9at% Mo and Fe-1at% Cu at 500 °C

Abstract

The early stages of precipitate formation in Fe-25at% Co-9at% Mo at 500 °C was investigated by in situ small-angle neutron scattering (SANS). The ratio of magnetic to nuclear SANS intensity, which depends on the precipitate composition, and the precipitate sizes were analyzed. The results suggest that in the Fe-Co-Mo alloy an initial stage of precipitate formation with strong compositional changes is completed after 150 s, when the full magnetic signal is established. For comparison, the well-known nucleation and growth reaction in Fe-1at% Cu was studied. Differences in the growth rate of the mean size of the developing structures could be distinguished in the two investigated alloys. While in the Fe-Co-Mo alloy the precipitate structures grow with t0.15 to t0.21, the mean precipitate radius in the Fe-Cu alloy grows with t0.40 in the observed time interval.