Effect of high temperature annealing on microstructure and mechanical properties of Morlion735 alumina fiber

Continuous alumina fiber-reinforced alumina (Al2O3/Al2O3) composite is a very promising candidate for thermal structural materials in aerospace vehicles and other applications. Alumina fibers used in Al2O3/Al2O3 composites play a crucial role in enhancing their mechanical properties and thermostability. In this article, the effect of annealing on the tensile strength and microstructure of Morlion735 alumina fiber was investigated. The results showed that the phase transformation occurs at 1147 °C, resulting in a mullite phase with an orthogonal lattice structure. As the annealing temperature increases, the crystal domain size of the mullite gradually increases. Both the phase transformation and the increasing crystal domain size lead to more lattice defects, which significantly affect the tensile strength and tensile modulus of alumina fibers. A 0.67 GPa reduction in tensile strength (from 1.14 GPa to 0.47 GPa) was observed when the annealing temperature increased from 1200 °C to 1400 °C. Weibull statistical analysis revealed that as the annealing temperature increased, the tensile strength dispersion of Morlion735 fiber also increased. This can be attributed to the volume-dependent flaw distributions. These results provide an in-depth understanding of the tensile strength evolution mechanism under high temperatures.