Nucleation and growth of GP (1) zones and growth of θ″ and θ′ phases in Al–4% Cu single crystal under applied stress

Abstract

The effects of an external stress on the nucleation and growth of disk-shaped GP (1) zones and growth of disk-shaped θ″ and θ′ precipitates have been examined for an Al–4 mass% Cu alloy single crystal. Application of a compressive stress along the[001]_α direction of the aluminum matrix during aging promotes particularly the nucleation and growth of the GP (1) zones on (001) _α and the growth of the θ″ and θ′ precipitates parallel to (001) _α. However, a tensile stress does not have a significant effect on those of GP (1) zones and that of θ″ and θ′ precipitates. Using the single crystal that has only the disk-shaped GP (1) zones perpendicular to [001]_α, the misfit strains, ε₁₁ (=ε₂₂) and ε₃₃, along[100]_α and[001]_α for GP (1) zones, θ″ and θ′ precipitates have been successfully estimated from measurements of length change and lattice parameter during aging. The acceleration of the nucleation and growth of the specific GP (1) zones and the growth of the particular θ″ and θ′ variants can be well understood through the interaction energy between the stress acting on the GP (1) zones, θ″ and θ′ variants and the misfit strains of them.