Oxidation behaviour of FeAl intermetallics - the effect of Y on the scale spallation resistance

The high-temperature oxidation behaviours of Fe-37Al and Fe-37Al-0.1Y (at.1 %) inter metallics have been studied at 1100 degreesC in static ambient air . A set of Fe-37Al specimens was oxidised for various periods of time, unde r thermal cycling conditions, to investigate the scale spallation propertie s. The oxide products were examined using X-ray diffraction, scanning elect ron microscopy and atomic force microscopy. The acoustic emission technique was used to monitor the development of cracks in the oxide scales in situ. The results showed that, for the undoped FeAl scale, cracking and spallati on took place at high temperature and during cooling, caused by growth and thermal stresses. For doped FeAl specimens, scale cracking or spallation oc curred during the cooling stage. Scale failure for these specimens was caus ed mainly by thermal stress. Physical models have been established to descr ibe this mechanism. The effects of Y on the scale morphology and scale spal lation tendency are discussed based on the experimental results. (C) 2001 E lsevier Science Ltd. All rights reserved.