Creep deformation in an alumina-silicon carbide composite produced via a directed metal oxidation process

Flexural creep studies were conducted in a commercially available alumina matrix composite reinforced with SiC particulates (SiCp) and aluminum metal at temperatures from 1200 degrees to 1300 degrees C under selected stress levels in air. The alumina composite (5 to 10 mu m alumina grain size) containing 48 vol% SiC particulates and 13 vol% aluminum alloy was fabricated via a directed metal oxidation process (DIMOX(TM))dagger and had an external 15 mu m oxide coating. Creep results indicated that the DIMOX Al2O3-SiCp composite exhibited creep rates that were comparable to alumina composites reinforced with 10 vol% (8 mu m grain size) and 50 vol% (1.5 mu m grain size) SiC whiskers under the employed test conditions. The DIMOX Al2O3-SiCp composite exhibited a stress exponent of 2 at 1200 degrees C and a higher exponent value (2.6) at greater than or equal to 1260 degrees C, which is associated with the enhanced creep cavitation. The creep mechanism in the DIMOX alumina composite was attributed to grain boundary sliding accommodated by diffusional processes. Creep damage observed in the DIMOX Al2O3-SiCp composite resulted from the cavitation at alumina two-grain facets and multiple-grain junctions where aluminum alloy was present.