Effect of heat-treatment on the microstructure and room-temperature mechanical properties of alumina-silica fiber

Effect of heat-treatment (900 degrees C similar to 1600 degrees C) on the microstructure and mechanical properties of alumina-silica fiber was well investigated. The results indicated that the recommended temperature threshold for the use of the alumina-silica fiber was not more than 1100 degrees C to maintain its mechanical integrity. Above this temperature, the elastic modulus of the fibers increased, and the tensile strength significantly decreased, mainly because of the transformation of the structure from gamma-Al2O3 and amorphous SiO2 to mullite. The tensile strength of the fiber was 0.87 GPa at 1200 degrees C. Compared to the as-received fibers, the strength retention was only 63.50%. Moreover, as revealed by Weibull statistical analysis, the formation of more defects due to mullite phase transformation resulted in higher dispersion of the fiber tensile strength. However, at this temperature, the Young's modulus of the fiber increased from the initial value 146.24 +/- 5.19 GPa to 183.06 +/- 5.83 GPa. Finally, the rate of mullite reaction was seen to be strongly temperature dependent. The higher the heat-treated temperature, the shorter the time required for gamma-Al2O3 and amorphous SiO2 to completely transform into mullite grains.