The ternary systems Al-M-Si (M = Co, Fe, Ti)

Ternary systems of the 3d transition metals with aluminum and silicon are of significant importance for many technical applications and may be regarded as technological key systems. Nevertheless, the information on structure, properties and phase equilibria of the stable ternary compounds in the systems Al-M-Si (M = Co, Fe, Ti) is still far from complete. The primary goal of the proposed research project is an experimental investigation of ternary phase equilibria with the aim to reach a complete and consistent description of the phase diagrams based on a combination of isothermal and vertical sections and including a list of invariant reactions as well as liquidus surface projections. This will also include certain thermodynamic measurements necessary to promote future thermodynamic modeling of the systems. Our second goal is the investigation of the structure of insufficiently characterized phases and the synthesis and characterization of possible new ternary phases in the systems Al-M-Si (M = Co, Fe, Ti). This includes the detailed study of homogeneity ranges at different temperatures, the investigation of the underlying mechanisms of nonstoichiometry by means of crystallographic methods, and a basic physical characterization. Furthermore it will be our goal to gain deeper insight into the chemical bonding and the structure-composition relations of complex ternary aluminides in the Al-Fe-Si and Al-Co-Si systems using quantum chemical calculations.

Systems containing transition metals in combination with aluminum and silicon are of interest for many technical applications, such as aluminum-based alloys and different high-temperature materials. Phase diagrams provide a full description of the equilibrium situation in multi-component systems as a function of composition and temperature and are therefore form an important basis for the development and optimization of new materials. In the current project, phase diagrams of the ternary systems Al-Co-Si, Al-Fe-Si, Al-V-Si, Al-Mo-Si and Al-Cu-Si and of the quaternary system Al-Fe-Ti-Si were studied experimentally. These studies included the synthesis and characterization of new compounds, the investigation of homogeneity ranges and structural parameters of intermetallic phases, the systematic investigation of melting behavior and phase reactions and the investigation of diffusion profiles. Furthermore, mechanical properties of selected alloys were studied and thermodynamic modeling was performed in selected systems. In the course of cooperations we were also able to investigate the systems Al- Fe-Ni-Ti, Al-Ge-Ni and Al-Ge-Ti which are interesting in the context of high temperature alloys and the development of new joining techniques. The basic studies performed during the current project yielded many new and interesting results and a detailed description of phase equilibria in the different systems could be reached. These phase diagrams form an important basis for further application-related investigations of aluminides and their alloys.