[Untitled]

This study reports the effects of up to 4 at.%rhenium addition on the cyclicoxidation behavior ofβ-NiAl + α-Cr alloys having a basecomposition (in at.%) Ni-40Al-17Cr. Tests were conductedin still air at 1100°C for up to 250 1-hr cycles.The ternary alloy (without rhenium addition) exhibitedpoor cyclic-oxidation resistance, undergoing extensivescale spallation and internal oxidation. Additions of rhenium considerably improved the oxidationbehavior, reducing the extent of both scale spallationand internal oxidation. These beneficial effectsincreased with increasing rhenium content. Rhenium additions improved cyclic-oxidation resistanceby both decreasing the solubility of chromium in theβ phase and causing the interdendritic α-Crprecipitates in the alloy microstructure to become more spheroidized and disconnected. Theseeffects aided in preventing both interdendritic attackand the dissolution of the α-Cr precipitates fromthe subsurface region of the alloy. The maintenance of α-Cr precipitates at the alloy-scaleinterface decreased the extent of scale spallation byproviding a lower coefficient of thermal-expansion (CTE)mismatch between the alloy and theAl2O3-rich scale.