Current positron studies of structural modifications in age-hardenable metallic systems

The sensitivity of positron annihilation characteristics to the structural changes occurring in supersaturated metallic systems has been demonstrated and explained since the early 1980s. This knowledge is currently applied for positron annihilation spectroscopy (PAS) investigations regarding the main phenomena that govern the structural evolution of a supersaturated alloy when various thermal treatments are applied: (a) kinetics of vacancy-type defects retained after quenching; (b) solute migration; (c) formation of solute clusters and/or GP zones; (d) precipitation. The analysis of PAS data gives information on the chemical composition, the defect structure and the density of decomposition products of nanometric size. The present article, that includes an exhaustive repertory of works published since 1987, discusses the value of the contribution that PAS studies can give to physical metallurgy in the field of age-hardenable systems. Most examples are taken from the direct experience of the authors. Materials discussed: a variety of aluminum alloys.