Microstructure and Enhanced Mechanical Properties of Al 2 O 3 /Al 2 O 3 Composite Densified via Sol‐Gel Method

There is a trade‐off between the fiber‐ and matrix‐dominated mechanical properties of the alumina‐fiber‐reinforced alumina ceramic matrix (Al 2 O 3 /Al 2 O 3 ) composites, which have two‐dimensional fiber fabrics and porous matrix. In this work, a novel Al 2 O 3 sol was used to densify the Al 2 O 3 /Al 2 O 3 composites. The thermal evolution of the Al 2 O 3 sol as well as the microstructures and mechanical properties of the Al 2 O 3 /Al 2 O 3 composite were investigated. The sol exhibited a low phase‐transition temperature: α‐ Al 2 O 3 appeared at 1000°C and became fully developed at 1100°C. After densification, the composite density increased from 3.01 ± 0.07 to 3.18 ± 0.01 g/cm 3 , and the matrix hardness increased from 2.6 ± 0.2 to 4.2 ± 0.2 GPa. The sol densified Al 2 O 3 /Al 2 O 3 composites displayed high flexural strength of 453.4 ± 32.4 MPa, and high interlaminar shear strength of 30.3 ± 0.7 MPa, which were 53.5% and 98.0% greater than those of the as‐fabricated Al 2 O 3 /Al 2 O 3 composite. Mechanistically, sol‐derived nanoscale alumina particles fill residual pores/microcracks, densifying the matrix and improving load transfer. The fiber/matrix contact tightens but remains weakly bonded, promoting crack deflection and suppressing delamination. These findings suggest that the balance between the fiber‐ and matrix‐dominated mechanical properties of the Al 2 O 3 /Al 2 O 3 composites can be achieved by the Al 2 O 3 sol densification.