CONSTRUCTION AND APPLICATION OF METASTABILITY FIELD DIAGRAMS FOR NONEQUILIBRIUM PROCESSING OF ALLOYS

Isothermal metastability field diagrams first proposed by Baker and Ca hn depicting the thermodynamic limits to co-existing interfacial solid and liquid compositions have been critically analysed. The properties of these diagrams under different limiting conditions have been deriv ed. Construction of paired diagrams by simultaneous consideration of b oth the competing solid phases of a binary eutectic has been demonstra ted to be useful. The possibility of the recurrence of eutectic-like s olidification as in the Pb-Sn system, or formation of continuous solid solutions as in the Ag-Cu system, at moderate undercoolings can be in ferred from the paired diagrams. A novel construction of non-isotherma l metastable field diagram has been proposed to determine the thermody namic limits to the distribution coefficient in alloys during freezing as a function of undercooling. Regions of solute and solvent napping and the diffusional domain can also be delineated in these diagrams.