Microstructure, growth mechanism and mechanical property of Al2O3-based eutectic ceramic in situ composites

Directionally solidified Al2O3-based eutectic ceramic in situ composites with inherently high melting point, low density, excellent microstructure stability, outstanding resistance to creep, corrosion and oxidation at elevated temperature, have attracted significant interest as promising candidate for high-temperature application. This paper reviews the recent research progress on Al2O3-based eutectic ceramic in situ composites in State Key Laboratory of Solidification Processing. Al2O3/YAG binary eutectic and Al2O3/YAG/ZrO2 ternary eutectic ceramics are prepared by laser zone melting, electron beam floating zone melting and laser direct forming, respectively. The processing control, solidification characteristic, microstructure evolution, eutectic growth mechanism, phase interface structure, mechanical property and toughening mechanism are investigated. The high thermal gradient and cooling rate during solidification lead to the refined microstructure with minimum eutectic spacing of 100 nm. Besides the typical faceted/faceted eutectic growth manner, the faceted to non-faceted growth transition is found. The room-temperature hardness HV and fracture toughness KIC are measured with micro-indentation method. For Al2O3/YAG/ZrO2, KIC = 8.0 ± 2.0 MPa m1/2 while for Al2O3/YAG, KIC = 3.6 ± 0.4 MPa m1/2. It is expectable that directionally solidified Al2O3-based eutectic ceramics are approaching practical application with the advancement of processing theory, technique and apparatus.