High-temperature oxidation behavior of the intermetallic compound NbAl3: Influence of two processing techniques on the oxidation mechanism

The NbAl3 intermetallic compound was prepared two different ways: first, by the classical induction-melting, technique; the end product is a coarse-gr ain massive compound including cracks and pores. Second, by mechanically ac tivated annealing process (M2AP); the end product is a fine-grain, powder o f submicron crystallites. The oxidation behavior in air under atmospheric p ressure over the temperature range 500-1350 degrees C was studied for each material in order to determine the influence of the NbAl3 microstructure on the oxidation mechanism. In all cases, the massive compound does not form the expected compact alumina, protective scale. In the lower temperature ra nge, the "pest" phenomenon occurs. No grain disintegration was evidenced by oxidation of the M2AP NbAl3 powder despite the high number of crystallites forming one grain. This is a good argument with expected behavior for a ma ssive material produced from the M2AP precursor by powder metallurgy proces sing.