Effect of RE2O3 addition on the microstructure and thermal stability of continuous alumina fibers

Abstract Continuous alumina fibers with excellent thermal stability are essential in high-temperature applications. In this study, 0~1 wt% RE2O3 (RE = Y, Er, Yb, and Ho) were added to the alumina fibers to enhance thermal stability. The impact of RE2O3 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 RE2O3 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% RE2O3 exhibited a remarkable strength retention rate of up to 93% after exposure to 1200 °C for 10 h. The TEM analysis revealed that RE 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.