PHASE-FORMATION IN DROP-TUBE PROCESSING FROM UNDERCOOLED PD77.5AU6SI16.5 MELT

The Pd77.5Au6Si16.5 alloy was studied by drop-tube processing. Palladium solid-solution phase was found in smaller droplets (diameter D < 400 m), while in larger droplets, the intermetallic compound Pd3Si was observed. The difference in free energy between the undercooled liquid and the solid state, the activation energy for the formation of post-critical nuclei, the nucleation frequency and the crystal growth velocity, were calculated as functions of temperature for palladium solid solution and Pd3Si phases. These calculations led to time-temperature-transformation curves which were capable of describing the experimental findings on the kinetics of solidification of this alloy.