Effects of sintering temperature on mechanical properties of alumina fiber reinforced alumina matrix composites

In this study, the continuous alumina fibers reinforced alumina matrix (Al2O3/Al2O3) composites were fabricated through sol–gel method at a sintering temperature range of 900–1400 °C, and their mechanical properties were analyzed separately. To explore the effects of sintering temperature on mechanical properties of composites, the high temperature properties of fibers and matrix were studied in a comprehensive manner. Our results suggested that the composites fabricated at different temperatures exhibited two different fracture features (ductile fracture and brittle fracture). Besides, the 1100 °C fabricated composites possessed the highest flexural strength of nearly 150 MPa. Al2O3 fibers displayed excellent thermal stability, and did not undergo phase transition during the preparation process. However, the grain size of fibers increased dramatically at a sintering temperature of 1200 °C, which led to a significant decrease in the mechanical properties. In the meantime, the surface morphology of fibers became very uneven because of grain coarsening. Due to the phase transition from γ-Al2O3 to α-Al2O3 at 1200 °C, the elastic modulus and microhardness of matrix increased significantly. The higher sintering temperature not only intensified the matrix but also strengthened the interface bonding, thus making the composites prone to brittle fracture. In conclusion, the optimal temperature of composites preparation should be lower than 1200 °C.