Micro- and macrosegregation of a peritectic Au-Fe alloy during Bridgman solidification

In jewelry manufacturing, joining dissimilar materials is usually achieved by soldering or brazing, but these techniques have several disadvantages as compared for example with laser welding. In this last case, however, it is necessary to have a thorough understanding of microstructure formation during solidification. Microstructure analysis of quenched Bridgman solidified specimens provides access to a wide range of information on solidification phenomena, as for example micro- and macrosegregation. The present study focuses on a peritectic Au-Fe alloy solidified at low speed in a high thermal gradient. Micro- and macrosegregation are investigated through microstructure analysis and modeling. On one hand, microsegregation along secondary dendrite arms is measured with a microprobe. These results are compared with simple 1D front-tracking numerical simulations of microsegregation, coupled with the available phase diagram and accounting for the peritectic reaction. On the other hand, strong macrosegregation is observed (hiring solidification of Au-Fe alloy, due to the high density difference between iron and gold. An analysis based on solidification shrinkage and the model of Flemings and Nereo is presented.