Role of Strain-Compensated Clusters in Al-Alloy Design

Atom probe tomography has been combined with high resolution transmission electron microscopy (HRTEM) to confirm the existence of such clusters by atomic resolution observation. HRTEM images indicate that the solute clusters are ~3 nm in diameter and contains ~850 atoms. The clusters have diffuse boundaries, maintain the same crystal structure as the host lattice and are roughly spherical in shape. Clusters were face-centered cubic and contained up to 80 at.% Al, whereas the precipitates were diamond cubic and contained no Al. Although the existence of strain-compensated Si-Ge clusters had been postulated previously, this direct observation clarifies their role in the microstructural evolution and provide a more systematic use of this phenomenon