Metastable phase equilibria in the lead-tin alloy system: Part I. Experimental

Several metastable phase boundaries in the Pb-Sn alloy system have been determined in undercooled droplets containing different phase mixtures by means of X-ray diffraction lattice parameter and thermal analysis measurements. With droplets equilibrated as (α-Pb + L) mixtures, the metastable α-Pb solidus has been determined to reach 46 at. pct Sn with a corresponding liquidus at 87 at. pct Sn for a temperature 73°C below that for the stable eutectic. An extension of the metastable liquidus and solidus boundaries implies a melting of fcc Sn at about 5°C which agrees well with thermodynamic model calculations. The combination of the measured stable equilibria, the partial metastable equilibria determination, and phase equilibria modeling has allowed for a more complete description of metastable equilibrium behavior and for the analysis of some of the solidification pathways that are available for the synthesis of metastable product structures.