Phase equilibria and structural investigations in the Ni-poor part of the system Al-Ge-Ni

The ternary phase diagram Al-Ge-Ni was investigated between 0 and 50 at.% Ni by a combination of differential thermal analysis (DTA), powder- and single-crystal X-ray diffraction (XRD), metallography and electron probe microanalysis (EPMA). Ternary phase equilibria and accurate phase compositions of the equilibrium phases were determined within two partial isothermal sections at 400 and 700 °C, respectively. The two binary intermediate phases AlNi and Al₃Ni₂ were found to form extended solid solutions with Ge in the ternary. Three new ternary phases were found to exist in the Ni-poor part of the phase diagram which were designated as τ₁ (oC24, CoGe₂-type), τ₂ (at approximately Al_67.5Ge_18.0Ni_14.5) and τ₃ (cF12, CaF₂-type). The ternary phases show only small homogeneity ranges. While τ₁ was investigated by single crystal X-ray diffraction, τ₂ and τ₃ were identified from their powder diffraction pattern. Ternary phase reactions and melting behaviour were studied by means of DTA. A total number of eleven invariant reactions could be derived from these data, which are one ternary eutectic reaction, six transition reactions, three ternary peritectic reactions and one maximum. Based on the measured DTA values three vertical sections at 10, 20 and 35 at.% Ni were constructed. Additionally, all experimental results were combined to a ternary reaction scheme (Scheil diagram) and a liquidus surface projection.