AL(FCC)AL3SC(L1(2)) INTERPHASE BOUNDARY ENERGY CALCULATIONS

These calculations assess the applicability of classical nucleation th eory to the reaction f.c.c. --> L1(2) occurring in dilute Al-Sc alloys . The orientation and temperature dependence of the energies of cohere nt Al(f.c.c.):Al3Sc(L1(2)) interphase boundaries were studied using at omistic simulation and a low temperature expansion (LTE) of the grand potential. Embedded atom method potentials were developed for both set s of calculations. Atomistic 0 K results for the anisotropy of the int erphase boundary enthalpy gave gamma((100)) < gamma((110)) <gamma((111 )) with values of 32.5, 51.3 and 66.3 mJ/m(2), respectively. LTE calcu lations of the excess grand potential of the (100) interface predicted a nearly temperature independent interfacial energy below 400 K that decreased modestly above 400 K. Monte Carlo (MC) simulations produced a compositional diffuseness of about 4 atomic layers separating the tw o bulk phases. Because the spatial extent of this region is very simil ar to the classically determined critical nucleus dimensions extracted from nucleation rate data, it is concluded that critical nuclei of Al 3Sc are most likely of nonclassical design at high undercooling. (C) 1 998 Acta Metallurgica Inc.