Institute of Metals Division - Fluid Flow Control During Solidification Part II: Programmed Solute Distribution

A theoretical analysis of alloy solidification in which the effective partition coefficient, k, of the solute is allowed to vary as a function of interface position is performed. A variety of solute distm'butions in the solid is predicted depending upon the functional dependence of k with interface position. Conversely, the variation of k with interface position required to produce a particular solute distributzon in the solid can be calculated. These preciictions have been tested by controlling the width of the momentum boundary layer in the liquid as a function of interface position with a rotating mugnetic field. One of the objects of controlled solidification is to utilize the freezing process for the preparation of crystals of specific materials containing a predetermined distribution of solutes. For example, a thermoelectric power generation material may exhibit a figure of merit, 2,' as a function of temperature, T, and solute concentration, C, as illustrated in Fig. 1. If we wish to use this material in a device between the temperature limits T1 to T2 a significantly greater efficiency will result from the device if the thermoelectric element illustrated in Fig. 1 consists of a range of solute concentrations appropriately located with respect to the temperature distribution rather than using a sample of constant solute concentration. For this reason and many others2 we are interested in programming and controlling the solute distribution in a single crystal