Abstract
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 Nb2Al, 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 (Nb3Al and Nb3Sn). Tin showed limited solubility in NbAl3, not exceeding 3.6 at.% as it substituted Al atoms. The solubility of Al in NbSn2 varied from 4.8 to 6.8 at.%. A ternary phase, Nb5Sn2Al with the tI32 W5Si3 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.
Highlights
Nb-silicide based materials have been extensively studied as generation alloys for aero engines due to their high melting temperatures, and excellent strength and creep resistance at high temperatures [1,2,3,4,5,6]
The Al-Nb-Sn phase diagram is of interest and important for both the alloy design of these materials and possible coating systems
Nb-17Al-17Sn (IP4), Nb-33Al-13Sn (IP5) and Nb-16Al-20Sn (IP6). These alloys were studied in as-cast states (AC) and after heat treatments (HT) at 900 ◦ C and 1200 ◦ C
Summary
Nb-silicide based materials have been extensively studied as generation alloys for aero engines due to their high melting temperatures, and excellent strength and creep resistance at high temperatures [1,2,3,4,5,6]. Tin is shown to improve oxidation resistance in the pesting regime (temperature range 750–950 ◦ C) [2,8,9,10,11]. Aluminium is shown to improve both the oxidation resistance at higher temperatures whilst lowering the density of the alloys [12]. Oxidation resistance cannot be improved through alloying alone, and coatings will be required. The Al-Nb-Sn phase diagram is of interest and important for both the alloy design of these materials and possible coating systems. This work is part of a larger project to understand the phase equilibria in Nb-based alloys, and to improve oxidation resistance and mechanical properties of these materials through alloy design
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