MICROSTRUCTURAL EVOLUTION AND TRANSFORMATION PATHWAYS IN THE NEAR MONOTECTIC ZN RICH ZN-BI ALLOYS DURING RAPID SOLIDIFICATION

The possible pathways for microstructural development under nonequilibrium condition by the rapid solidification of alloys containing liquid miscibility gap have been studied using Zn-Bi binary alloys as a model system. The primary aim is to explore the possibility of the intermediate formation of a thermodynamically unstable solid solution as a precursor phase which can spontaneously decompose to yield nanodispersions. It is shown that the information of crystallographic shape of the nanosized dispersions obtained by transmission electron microscopy and the derived point groups can be utilised to arrive at a definite conclusion of this possibility. Our results establish the formation of such a solid solution owing to the kinetic process of nonequilibrium trapping in spite of a very strong clustering tendency. The latter leads to the spontaneous decomposition of the solid solution during quenching to yield nanodispersions.