Fundamental investigations of solute clustering and nucleation of precipitation

The major aim of the project is to contribute to the understanding of how solute atoms diffuse and interact in solid solution, and how they form aggregates that subsequently nucleate or grow into precipitates. Only recently, techniques for detailed invest igations, sufficient computing power for required atomistic calculations, and models with background from experiments have become available. The group 4B elements C, Si, Ge, Sn form the only mono-atomic diamond structures in the periodic table. Previous work in Al-Mg-Si indicates that Si seeks to form clusters or nano-crystals in the solid Al solution. The exact details are unknown, but information about orientation and structure (must resemble the diamond structure) has been inferred from the much larg er precipitates they are nucleating. The cluster formation of Si from the supersaturated solid solution is previously unknown. By means of one postdoc and one PhD, using quantum mechanical methods, an in-depth investigation on solute ordering and the cl usters is proposed. Models for clusters are available, as they are derived from the common structural similarities of recently solved precipitate structures. The methods and results from the postdoc study, held together with advanced TEM and atom probe ex periments on the finest Si-crystals of appropriate alloys and conditions, will be built on in the PhD program. Here focus will be on binary Al-alloys with two other diamond elements (Ge, Sn). The heavier solute elements imply that experimental information on the clusters are easier to get by Atom Probe, by HRTEM and other TEM techniques, such as the HAADF method. This view on nucleation and precipitation is new and the project is expected to be of general importance. It should add to the understanding of clusters of Si and the covalent bond and may have possible significance for the Norwegian aluminum industry. It is expected to generate further ideas and interest in nucleation in solids.