Effect of Y_0.5Er_0.5Ho_0.5Yb_0.5O₃ addition on the microstructure and thermal stability of continuous alumina fibers

Continuous alumina fibers with excellent thermal stability are essential in high-temperature applications. In this study, 0~1 wt% Y_0.5Er_0.5Ho_0.5Yb_0.5O₃ were added to the alumina fibers to enhance thermal stability. The impact of Y_0.5Er_0.5Ho_0.5Yb_0.5O₃ addition on alumina fibers’ transformation and microstructure evolution of during the sintering process was systematically studied. The influence of single- and two-step sintering processes on the fiber microstructures was elucidated. The results suggested that adding Y_0.5Er_0.5Ho_0.5Yb_0.5O₃ impeded fiber densification, inhibited alumina grain growth, and enhanced the thermal stability of fibers. Using a two-step sintering process facilitated the achievement of fully dense alumina fibers with fine grains. The alumina fibers added with 1.0 wt% Y_0.5Er_0.5Ho_0.5Yb_0.5O₃ exhibited a remarkable strength retention rate of up to 93% after exposure to 1200 °C for 10 h. The TEM analysis revealed that rare earth elements segregation at α-Al₂O₃ grain boundaries due to their larger radius than the Al element contributed to stabilizing the microstructures of α-Al₂O₃ fibers at high service temperature.