Deformation-induced Au precipitation kinetics in Fe-Au-W alloys studied by time-resolved small angle neutron scattering

In-situ time-resolved small-angle neutron scattering (SANS) experiments were conducted on homogenised coldrolled ternary Fe-Au-W alloys during aging for 12 h at temperatures of 650 to 700 degrees C in order to study the kinetics of the nanoscale precipitation. For comparison the precipitation kinetics in the binary counterparts Fe-Au and Fe-W alloys were also studied. In the ternary Fe-Au-W alloy nanoscale Au-rich precipitates were observed by both transmission electron microscopy (TEM) and SANS, while no significant W-rich precipitation was observed. The SANS pattern of the cold-rolled Fe-Au-W alloy clearly reveals a preferred orientation for the plate-shaped nanoscale Au-rich precipitates. As these Au-rich precipitates have a fixed orientation relation with the matrix lattice this preferred orientation originates from the texture of the bcc matrix grains, as confirmed by X-ray diffraction (XRD) pole figure measurements. The effect of texture on the nuclear and the magnetic SANS signal during the precipitation kinetics was included in the data analysis. This enables us to monitor the temperature dependence of the precipitation kinetics for the Au-rich precipitates in the Fe-Au-W alloy during aging at temperatures of 650, 675 and 700 degrees C. It is found that an increase in aging temperature results in a faster kinetics and a lower final precipitate fraction.