Alumina is one of the most attractive oxide ceramics for structural, electrical, optical, and biomedical applications due to its high hardness, wear resistance, electrical resistivity, and chemical stability. On the other hand, low toughness under thermal and mechanical stresses is the main drawback of alumina ceramics. The common approach to improve its fracture toughness is the introduction of secondary phases which give high fracture resistance to the brittle matrix. A commercial Al2O3-SiCw cutting tool is a well-known example for this approach. Nevertheless, expensive raw materials and high equipment costs result in a strong demand for the development of alternative fracture resistant alumina-based ceramics. At that point, reinforcing of brittle alumina matrix by in-situ formed rod-like rare-earth aluminate ((RE)Al11O18) phases has a high potential to improve fracture toughness. In this study, it was aimed to develop Al2O3 ceramics toughened by well-dispersed RE-aluminate phase by direct mixing of different rare earth element oxides such as La2O3, Y2O3, Yb2O3, CeO2, Sm2O3 and Er2O3 into compositions. Spark plasma sintering (SPS) and gas pressure sintering (GPS) methods were performed comparatively to densify the samples. The results revealed that the formation of REAl11O18 phase strongly depend on the type of the RE element and require larger cations like La+3 and Ce+2. While SPS allowed efficient densification, the growth of aluminate phase in high aspect ratio was insufficient to activate the toughening mechanisms. On the other hand, despite the high sintering temperature and gas pressure, full densification could not be achieved with GPS, indicating that sintering additives are required for further densification.
Acknowledgements: The financial support for this study by Eskişehir Technical University Scientific Research Projects Commission (under the Project No. 21GAP068) is gratefully acknowledged. ORCID ID: 0000-0001-6206-1587
Anahtar Kelimeler: Alumina, Fracture toughness, Rare-earth aluminate, Sintering