EFFECTS OF COMPOSITION ON ISOTHERMAL SOLIDIFICATION KINETICS OF HIGHLY UNDERCOOLED ALLOYS

A modified theory incorporates the effects of composition on homogeneo us nucleation and isotropic crystal growth in isothermal, massive soli dification of alloys. Simple, realistic values for the needed kinetic and thermodynamic quantities facilitate calculation of grain size and solidification times as a function of temperature and concentration. R easonable agreement is found between the isothermal theory and results of continuous cooling experiments on pure Al and some Al-based alloys . The conditions for producing a vitreous, non-crystalline solid are a lso given. We propose that the extremely fine grain sizes obtained in AL-Ge and Ag-Cu alloys rise from quenching to form a glass, followed b y isothermal crystallization at or near room temperature.