Abstract
The oxidation of the intermetallic compound NbAl 3 and of materials with some excess aluminium (NbAl 3 + Al) was investigated at temperatures between 650 and 1200 °C in He − 133.3 mbar O 2. At temperatures between 1000 and 1200 °C, the NbAl 3 single phase shows a quasi-linear oxidation rate caused by cracking and spallation of the protective oxide scale. The Nb 2Al phase is formed at the oxide - scale interface on which the fast-growing oxides AlNbO 4 and Nb 2O 5 are formed upon cracking of the oxide scale. The oxidation kinetics of (NbAl 3 + Al) can be described by α-Al 2O 3 growth according to the parabolic rate law between 1000 and 1200 °C. Between 650 and 1000 °C, NbAl 3 shows the phenomenon of disintegration with no appreciable bulk oxidation, known as “pest”. A maximum in the oxidation rate of the NbAl 3 single phase is observed at 750 °C. An excess of aluminium decreases the oxidation rate and no disintegration occurs.
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