Microstructure and High Temperature Properties of Nextel 720 Fibers

The high temperature tensile strength and creep properties of Nextel 720 were measured in the temperature range 1000°C — 1300°C. The creep rate for the Nextel 720 fibers was three orders of magnitude less than single phase polycrystalline alumina fibers such as Nextel 610, and 85% of room tensile strength was retained at 1200°C. These exceptional high temperature properties were attributed to a unique, two-phase microstructure consisting of mosaic and elongated grains of α-Al2O3 and mullite. The room temperature single filament strength of Nextel 720 averaged 2100 MPa, and the elastic modulus was 260 GPa.