Me-Si-B (Me-metal) alloy systems have been evaluated to aid the development of ultra high temperature structural materials. In the present work, the phase relations at 1700°C in the Nb-NbSi 2 -NbB 2 region of the Nb-Si-B system have been experimentally determined. The alloys were prepared via arc melting and powder metallurgy routes. All samples were characterized via scanning electron microscopy (SEM) and x-ray diffraction (XRD) and selected samples were also scanned via wave-length dispersive spectroscopy (WDS). The high B solubility in the aNb 5 Si 3 phase has been confirmed with solubility range larger than that proposed in the 1600°C isothermal section of Nowotny et al. (Aufbau und Zunderverhalten von Niob-Bor-SiliciumLegierungen, Mon. Chem., 1960, 91, p 975-990). In contrast to Nowotny's isothermal section, it has been observed that the D8 8 -phase should be nearly stoichiometric with composition close to 57Nb35Si8B (at.%). It was also found that the D8 8 -phase does not equilibrate with NbB 2 -phase at 1700°C. A negligible Si solubility in the boride phases as well as that of B in NbSi 2 has been noticed.
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