Fig. 1 (Ti, Zr)-Al-(Mo, Nb, Ta, W, Sn, Si, etc.) pseudo-ternary composition diagram showing the positions of the designed Ti5666 (red open squares, arrowed), Ti-6Al-4V, Ti65, IMI834, 7715D, and Ti750 high-temperature Ti alloys, as well as related 16-atoms α-Ti and 18-atoms β-Ti formulas

Fig. 2 Schematic diagrams of vacuum arc melting system a, vacuum pour casting system b

Fig. 3 OM and SEM images of Ti5666 a, b and Ti65 c, d at the as-cast state

Fig. 4 XRD spectra of Ti5666 and Ti65 at the as-cast state

Fig. 5 TEM micrographs of Ti5666 at the as-cast state: a TEM BF images and the corresponding SAED patterns showing electron diffraction of α phase, b HRTEM image taken from nearby the lath (“A” point, in a), c lattice image as selected by yellow box (in b) and corresponding FFT spectrum of SAED from B region of β phases, d lattice image as selected by white box (in b) and corresponding FFT spectrum of SADP from C region of α phases, and e lattice image as selected by blue box (in b) and corresponding FFT spectrum of SADP from D region of interface between α and β phases

Fig. 6 SEM micrographs of Ti5666 a-c and Ti65 d-f after the tensile tests, respectively, at 600 °C, 650 °C, and 700 °C

Fig. 7 IPF maps and pole figures for Ti5666 a, b and Ti65 c, d at the as-cast state

Fig. 8 Prismatic I {10-10}, prismatic II {11-20)} and pyramidal {11-21)} for fine α grain regions and coarser α grains regions in Ti5666 a-f and Ti65 g-l at the as-cast state. Fine α grains were selected as length ≤ 30 μm

Fig. 9 Engineering tensile stain-stress curves of as-cast Ti5666 and Ti65 at ambient temperature a, and at 600 ℃, 650 ℃ and 700 ℃ b, comparisons of mechanical properties between present Ti5666 and reported Ti alloys at the as-cast state c, and after 520-650 ℃ tests d. HIP denote hot isostatic pressing. Present work is marked with arrow

Fig. 10 Theoretical and experimental yield strength of the alloys at the as-cast state

Fig. 11 SEM images of fracture surfaces of Ti5666 a, b and Ti65 c, d as-cast alloys after tensile tests at ambient temperature

Fig. 12 Schematic diagrams of fracture mechanism of Ti5666 a and Ti65 b alloys with basket-weave microstructure