HOMOGENEOUS NUCLEATION KINETICS OF AL3SC IN A DILUTE AL-SC ALLOY

The homogeneous nucleation kinetics of the Ll2 Al3Sc phase in the face-centered cubic (fcc) matrix of an Al-0.11 at. pct Sc alloy were measured at 561 and 616 K using the isothermal transformation technique and transmission electron microscopy (TEM). Applying classical homogeneous nucleation theory in conjunction with available thermodynamic data, an average interphase boundary energy of about 94 +/- 23 mJ/m2 was estimated from the nucleation rate data. This energy was found to vary weakly with temperature. The effects of heat-treatment technique (isothermal transformation vs quench and age) on nucleation kinetics indicate that quenched-in vacancies may influence nucleation kinetics primarily by increasing the interdiffusion of Sc in Al.