Influence of crystallography upon critical nucleus shapes and kinetics of homogeneous f.c.c.-f.c.c. nucleation—III. The influence of elastic strain energy

Abstract

The influence of crystallography upon critical nucleus shapes and kinetics of homogeneous f.c.c.-f.c.c. nucleation was studied by combining the discrete lattice point non-classical model utilized in paper II of this series with the microscopic theory of strain energy as applied by Cook and de Fontaine to compositional fluctuations in cubic lattices. This permits simultaneous consideration of the influence of anistropic interfacial energy and anisotropic strain energy upon nucleation. This is extremely difficult to do using other models of strain energy because of mathematical problems. The model is applied to f.c.c. nuclei in Al Cu and Cu Co alloys. Nuclei in Al Cu are plates because coherency strain energy predominates in this system. In Cu Co alloys, the misfit is smaller and the distortion tensor is cubic; thus the nuclei are essentially spherical. Despite this lesser effect, the influence of strain energy upon the nucleation kinetics of Co-rich precipitates in a Cu-rich Cu Co alloy is found to be very important, reducing these kinetics by as much as five orders of magnitude.