Nickel aluminides, like γ'-Ni3Al and β-NiAl, are nowadays used in terms of nickel-base superalloys. Due to their excellent properties at high temperatures, they are applied in aircraft engines and power generating turbines, were materials are subjected to elevated temperatures and mechanical stresses. Since applied parts of nickel-base superalloys are moulded in complicated procedures at elevated temperatures, they are very expensive. A successful application of these materials thus requires suitable and cost-effective joining techniques, e.g. transient liquid phase bonding (TLP). As it is a brazing method, one has to determine a solder material which has a definitely lower melting point than the joining parts. In the present work, germanium has been chosen, as melting point depressing element, as it forms deep eutectics with Al and Ni. The aim of the present work was to investigate the ternary phase diagram Al-Ge-Ni, in order to optimize the filler composition and to better understand the interface reactions occurring during the brazing process.