GRAVITATIONAL INFLUENCE ON BINARY ALLOY MELT EQUILIBRIA AND EUTECTIC SOLIDIFICATION.

摘要

A concise history of ultra-centrifuge design is presented and complemented by a comprehensive review of its application in science, especially in materials science and the determination of liquid alloy cluster dimensions. A novel high-temperature ultra-centrifuge has been developed from the concept of a compact, low cost, air-turbine.; The equation governing sedimentation equilibrium in homogeneous liquid binary alloys is derived in differential form by defining a "gravochemical potential", (psi), which includes inertial terms in addition to the usual chemical potential, (mu). The resulting first order non-linear ordinary differential equation is solved and the results are presented graphically. Microstructures of Pb-Sn and Bi-Sn eutectic alloys are presented as experimental evidence supporting the numerical results and refuting conflicting data found in the literature on clustering in liquid alloys. These results are discussed with regard to the nucleation behavior of alloys and solidification fluid dynamics.; A series of eutectic alloys, mainly Pb-Sn and Bi-Sn were solidified under centrifuged fields with g(,max) ranging from 1 to 110,000 g(,e). The results are subdivided according to cooling rate, those representing normal ingot solidification and those approaching directional solidification. Plots of the segregation co-efficient versus gravity are presented for both cases. The unique behavior of alloy solidification at high levels of acceleration is revealed by numerous microstructural data. These pictorial results are discussed and interpreted on the basis of the relevant fluid dynamics of Stokes' settling, plume formation, and convection mass transfer, all three of which are reviewed briefly prior to their discussion.