The tensile creep behavior of two ceramic composite systems exhibiting duplex microstructures was studied relative to their single-phase constituents in the temperature and stress ranges of 1100-1350°C and 35-75 MPa. The equivolumetric compositions in the Al,O,:c-ZrO, (8 mol% Y,O,) and AI,O,:Y,AI,O,, systems both exhibit lower creep rates than either of their single-phase constituents. This effect is attributed to Y3+ (and possibly Zr4+) present in the AI,O, as a segregant which lowers the creep rate by -2 orders of magnitude. It is believed that the segregation of Y3+ to the AI,O, grain boundaries hinders the interface reaction believed to control the creep. If one of the singlephase constituents is taken to be the Y3+-doped A1,0,, the creep of the duplex microstructures can be modeled using standard composite theory applied to flow.
Grain growth in a 50:SO (~01%) dual-phase mixture of A1203 and c-ZrOz (cubic zirconia) is severely limited compared with that for either of the single phases. At 1650°C, the growth rates in the duplex composition are 160 and 3500 times lower than that for single-phase A1203 and c-Zr02, respectively. The restriction of the grain growth is attributed to the limited mutual solubility and the physical constraint provided by the interpenetrating geometry of the two phases. Grain coordination number and dihedral angle are also considered as factors affecting grain stabilization in two-phase systems. A potentially important practical application of this work is the fabrication of grain-stabilized fibers for use as reinforcement in composite structures at elevated temperatures. [
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