Preparation of high-strength alumina-zirconia fibers by the sol-gel method combined with two-step sintering processes

The preparation of high-performance Al 2 O 3 -ZrO 2 fibers is a significant and challenging task. In this study, continuous Al 2 O 3 -ZrO 2 fibers were synthesized via the sol-gel method using aluminum powder and zirconium acetate as raw materials. It was observed that the amorphous state of Al 2 O 3 transformed into γ-Al 2 O 3 and then to α-Al 2 O 3 , while the amorphous ZrO 2 directly transformed into t-ZrO 2 . The formation temperatures of t-ZrO 2 and α-Al 2 O 3 were both approximately 1100 °C. The optimal sintering temperature during the single-step sintering process for Al 2 O 3 -ZrO 2 fibers was 1400 °C. Based on the experiment results, fully dense Al 2 O 3 -ZrO 2 fibers with fine grains were successfully synthesized via a two-step sintering process. The average sizes of Al 2 O 3 and ZrO 2 grains were 153 nm and 62 nm, respectively. The Weibull strength of the Al 2 O 3 -ZrO 2 fibers reached 2.2 GPa with a peak value of 2.6 GPa, which exhibited an increase of approximately 30% compared to that formed by the single-step sintering process. Furthermore, the nucleation, growth, and densification behaviors of Al 2 O 3 -ZrO 2 fibers during the two-step sintering process were discussed.