In-situ measurements of solute partition coefficients between solid and liquid phases in Fe–Cr–Ni–Mo–Cu alloys during solidification

The in-situ measurements of the solute partition coefficients, k, between the solid and liquid phases in Fe–Cr–Ni–Mo–Cu alloys were conducted using X-ray transmission imaging and X-ray fluorescence spectroscopy (EDS) in a synchrotron radiation facility, SPring-8. A nearly planar solid/liquid interface was achieved in a furnace with a temperature gradient (5–10 K/mm) using X-ray transmission imaging. The measurement points in the solid and liquid phases and close to the solid/liquid interface were determined by X-ray imaging. The compositions of the solid and liquid phases were measured by EDS. The solute partition coefficients along the solidification path in the Fe - 19.89–25.82mass% Cr - 24.73–34.81mass% Ni - 4.46–10.28mass% Mo - 1.47–5.79mass% Cu alloy were determined at 56 different liquid compositions. At the beginning of solidification, the partition coefficients of Cr, Ni, Mo and Cu were 0.96, 0.97, 0.70 and 0.86, respectively. The partition coefficients of Cr and Ni were almost constant during the unidirectional solidification. The partition coefficient of Mo gradually changed from 0.7 to 0.6, leading to a severe microsegregation at the end of solidification. In contrast, the partition coefficient of Cu was dispersed in the range from 0.8 to 0.9. This study demonstrated that the in-situ measurement was effective for systematic measurement.