In Situ Growth of Root‐Like Whiskers on Al 2 O 3 Fiber‐Reinforced Oxide Composites: Mechanical and Thermal Performance

To address the interfacial high‐temperature degradation between the matrix and fibers in conventional alumina‐based composites, a hot‐press‐assisting forming process with aluminum sol slurry impregnation was developed to in situ grow “root‐like” Al 2 O 3 whiskers on Al 2 O 3 fibers, thereby fabricating whisker‐reinforced Al 2 O 3f /Oxide (Al 2 O 3w @A 2 O 3f /Oxide) composites, with the effects of sintering temperature, the addition of 3YSZ, and the repeated impregnation cycles of aluminum sol on grain growth, porosity, and mechanical properties of the composites. The 3YSZ effectively suppressed matrix grain coarsening through the Zener pinning effect, while the Al 2 O 3 whiskers prevented direct contact between the continuous aluminosilicate fibers (AF18) and the matrix. Even after a heat treatment, a gap interface between the fibers and matrix was still retained when the whiskers partially merged into the matrix. Hence, the Al 2 O 3w @AF18/Al 2 O 3 ‐3YSZ composites had a flexural strength up to 241.05 MPa, a fracture energy of 4311.7 J/m 2 , and a Vickers hardness of 6.76 GPa, all significantly higher than those of the Al 2 O 3w @AF18/Al 2 O 3 composites. However, the addition of whiskers and 3YSZ resulted in voids and mismatch in the thermal expansion among the constituent components, leading to a reduced thermal shock resistance of the composite. Nevertheless, the lower thermal conductivity of 3YSZ and abundant pores were related to the excellent thermal insulation and ablation resistance, highlighting its potential high‐temperature structural materials.