Effect of third elements on Cu precipitation in Fe-Cu alloys

In order to investigate the influence of third elements on Cu precipitation, small-angle neutron scattering (SANS) measurements and atom-probe (AP) analysis were carried out in conjunction with micro-hardness measurements during the early stage of phase decomposition in Fe-Cu based alloys. In the present paper, the effect of Ni, Mn and Ag are mainly reported. Data analysis of SANS intensities far the specimen added by Mn and Ni 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 fee copper-rich precipitate. This segregation was confirmed directly by atom-probe (AP) analysis. The calculated SANS intensities are well fitted to experimental data of both magnetic and nuclear components of neutron scatterings. Small addition of silver was deduced to cause an increase of coherency strain around bcc copper rich clusters.