Microstructural and mechanical characterization of a mullite fiber

The effect of thermal exposure on a mullite fiber was analyzed. This type of mullite fiber, consisting of gamma-Al2O3 and amorphous SiO2, was developed for high-temperature applications. Heat treatments at temperatures ranging from 900 degrees C to 1500 degrees C for 1h were performed in air. Investigations showed that the tensile strength of the initial fiber was about 1.60 GPa. And the elastic modulus was about 133.51 GPa. The bundles' strength decreased at 900 degrees C slightly after thermal treatment, then increased and got a maximum at 1100 degrees C with 1.65 GPa. At above 1100 degrees C, the strength degraded sharply due to the mullite phase transformation and the exaggerated grain growth. At 1300 degrees C, the phase reaction almost finished with a tensile strength of 0.86 GPa. And the strength retention was only 47.50%. When the heat-treated temperature got to 1500 degrees C, the density of surface defects in the fiber surged, making it too fragile and weak to go through the tensile tests.