| Summary: | The Al-Nb-Sn phase diagram was studied experimentally in the Nb-rich region to provide important phase equilibria information for alloy design of Nb-silicide based materials for aero engine applications. Three alloys were produced: Nb-17Al-17Sn, Nb-33Al-13Sn and Nb-16Al-20Sn (at.%). As-cast and heat-treated alloys (900 and 1200 °C) were analysed using XRD (X-ray diffraction) and SEM/EDS (scanning electron microscopy/ electron dispersive x-ray spectroscopy). Tin showed a high solubility in Nb<sub>2</sub>Al, reaching up to 21 at.% in the Sn-rich areas, substituting for Al atoms. Tin and Al also substituted for each other in the A15 phases (Nb<sub>3</sub>Al and Nb<sub>3</sub>Sn). Tin showed limited solubility in NbAl<sub>3</sub>, not exceeding 3.6 at.% as it substituted Al atoms. The solubility of Al in NbSn<sub>2</sub> varied from 4.8 to 6.8 at.%. A ternary phase, Nb<sub>5</sub>Sn<sub>2</sub>Al with the tI32 W<sub>5</sub>Si<sub>3</sub> crystal structure, was found to be stable. This phase was observed in the 900 °C heat-treated samples, but not in the 1200 °C heated samples.
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