文摘
Isothermal sections of the ternary Cr-Al-Nb phase diagram were experimentally investigated for temperatures of 1150, 1300, and 1450 ¡ãC by electron-probe microanalysis (EPMA), X-ray diffraction (XRD), differential thermal analysis (DTA) and light-optical (LOM) as well as scanning electron microscopy (SEM). Cr-Al-Nb alloys were prepared by levitation melting and annealed at temperatures between 1150 and 1450 ¡ãC for up to 1500 h. The most striking feature of the ternary Cr-Al-Nb phase diagram is the extended phase field of the cubic C15 and the hexagonal C14 Laves phase Nb(Cr,Al)2. With increasing Al content, the Laves phase polytype changes from C15 to C14. Both phase fields are separated by a small two-phase field, which shifts to lower Al contents with increasing temperature. The lattice parameters of both Laves phase polytypes and of all other phases occurring in this system were studied in dependence on composition and the solubilities of ternary elements in the binary phases were established.
