Diffusional relaxation around martensitically transformed Fe-Co particles in a Cu matrix

Small precipitate f.c.c. Fe-Co particles in a Cu matrix transform martensitically into b.c.c. particles by simple cooling a Cu-1.4 mass% Fe-0.6 mass% Co alloy to the liquid nitrogen temperature. Transmission electron microscopy has revealed that the small transformed particles are free from dislocations around them. However, the transformation strains create elastic fields in and around the particles. Successive annealing results in the occurrence of the diffusional relaxation of the elastic fields as envisaged by the changes in the Moiré fringes in the Fe-Co particles. The mechanism and kinetics of the diffusional relaxation are analyzed both experimentally and theoretically. It is found that diffusion at the interfaces between the Cu matrix and Fe-Co particles causes the relaxation and that the activation energy of the interfacial diffusion is 1.6eV.