The coarsening process of Ge precipitates in an Al– [formula omitted] Ge alloy

Abstract

In this paper the results of a quantitative transmission electron microscopy (TEM) investigation of the precipitation process of Ge in an Al– 4 wt. % Ge alloy are described. Two crystallographic orientation relationships between the irregular germanium precipitate and aluminum matrix were found to be [1 0 0] Ge || [1 1 0] Al and [1 1 4] Ge || [1 0 0] Al . The irregular germanium precipitates formed on [0 0 1] Al habit planes. The origin of the irregular shape is due to the existence of a highly anisotropic interfacial energy as well as in an isotropic growth rate along 〈1 1 0〉 A1 directions. Particles sizes were determined for variety of isothermal ageing times at 348, 423 and 523 K . The coarsening of the different morphologies of Ge precipitates was found to obey Ostwald ripening kinetics. The TEM results showed that the coarsening of irregular particles was due to the interfacial coalescence between these particles. Nine different morphologies have been distinguished in the form of (i) irregular particles, (ii) spheres, (iii) hexagonal plates, (iv) rods, (v) triangular plates, (vi) laths, (vii) small tetrahedra, (viii) rectangular plates, and (ix) Lamellae shape.