SANS Study of Phase Decomposition in Fe-Cu Alloy with Ni and Mn Addition

Small-angle neutron scattering (SANS) measurements were carried out to investigate the structural change during the early stage of phase decomposition in Fe-Cu-Ni-Mn quaternary alloy. Data analysis of scattering intensities showed that the nuclear Guinier radius becomes larger than the magnetic one beyond about 2 nm. This is suggested to be attributable to the formation of segregated layer enriched by Ni and Mn around fcc copper-rich precipitate. This segregation was confirmed directly by atom-probe (AP) analysis and approved from a thermodynamic point of view. The calculated SANS intensities are well fitted to experimental data of both magnetic and nuclear components of neutron scatterings. Addition of Ni and Mn in Fe-Cu binary alloy was suggested to promote the precipitation reaction of e-Cu phase.