A X-ray view on solutal melting in Cu-Pd

Solutal melting experiments on isomorphous copper-palladium (Cu-Pd) melting couples are performed to better understand the kinetics of the solid-liquid (s-l) interface. In-situ monitoring of the melting process with a sub-second time-resolution by X-ray radiography (XRR) is key to identify the evolution of the concentration fields during the process. The samples used, were concentric. XRR experiments were performed using thin samples of 220 and 460 thickness. The samples have been processed in a near-isothermal furnace by rapid heating with approximately 19.5 followed by annealing at holding temperature of 1090 slightly above the melting point of copper (Cu) (1085 ) but far below the melting point of palladium (Pd) (1555 ). Solutal melting of Pd was uniformly observed in real-time. In our study particular attention was paid to study the effect of specimen thickness on the s-l interface velocity. Pd dissolved rapidly in the thick sample of 460 in comparison with thin sample of 220 . Furthermore, the evolution of in-situ concentrations is determined using transmitted X-ray intensities. Postmortem analysis performed on re-solidified CuPd alloy using SEM gives satisfactory agreement. Persistent non-equilibrium conditions existed at the s-l interface by the end of melting regardless of melting mechanism and/or sample thickness.