Effect of moisture on the high-temperature stability of unidirectionally solidified Al2O3/YAG eutectic composites

The corrosion resistance of a unidirectionally solidified alumina/yttrium aluminum garnet (Al2O3/YAG) eutectic mixture was investigated at high temperature. Samples were exposed to high temperature (1200 degrees -1800 degreesC) in different atmospheres, which included argon, argon/water vapor, air, and air/water vapor. The most important microstructural changes occurred at the interface between the YAG and the Al2O3. Those changes consisted of localized thermal grooving, especially when the corrosive atmosphere contained water vapor. The samples exhibited significant weight loss at high temperature (1800 degreesC) after 20 h of exposure, The calculated volume gain that was induced by the increased surface relief was low and limited, except when the corrosive atmosphere contained air, which indicated that the presence of air (particularly oxygen) induced a more-active corrosion process. On the other hand, no change in the flexural strength was observed, even after 100 h at 1800 degreesC in a humid atmosphere, because of the cross-linked structure of the composite, which limited propagation of the groove.