Al–Ge–Ti: Phase equilibria and structural characterization of new ternary compounds

• Three partial isothermal sections of Al–Ge–Ti are established.
• Crystal structure of three new compounds is investigated.
• Partial Scheil diagram and liquidus surface projection are constructed.

Phase equilibria of Al–Ge–Ti have been investigated using scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and differential thermal analysis (DTA). Partial isothermal sections at 400 °C, 520 °C and 1000 °C were obtained with focus on the titanium-poor part up to 50 at.% titanium. Three ternary compounds were found to exist. The compound Al3GeTi (τ1) crystallizes in an own structure type (P4/nmm, tP10). Two structurally closely related compounds were found at the composition Al1−xGe1+xTi: τ2 (0.61 ≤ x ≤ 0.73), Al4Si5Zr3-type, I41/amd, tI  24 and τ2′ (0.36 ≤ x ≤ 0.57), Si2Zr-type, Cmcm, oC12. DTA data were used to construct a ternary reaction scheme (Scheil diagram) up to approximately 1300 °C, a partial liquidus projection and two vertical sections, at 10 at.% Ti and at a constant Al:Ti ratio of 1:1. A total number of 12 ternary invariant reactions were identified.