Effect of SiC addition on mechanical properties of hot-pressed Al2O3-GdAlO3 ceramics with eutectic composition

In the present work, Al2O3-GdAlO3 oxide nanopowders with eutectic composition of 77:23 (in molar ratio) were prepared via a chemical co-precipitation method. alpha-SiC particles were then incorporated with different volume fractions of 10, 15 and 20 vol% into the oxide powders. Al2O3-GdAlO3-SiC ceramics were hot-pressed at different sintering temperatures to obtain fully densified bulk ceramics. The as-sintered composites consist mainly of alpha-Al2O3, GdAlO3 and alpha-SiC phases, and exhibit a dense and uniform microstructure. The GdAlO3 grains are entangled with alpha-Al2O3 grains as indicated by SEM observations. SiC nanoparticles are found within the interior of both alpha-Al2O3 and GdAlO3 grains or at the interfaces between entangled alpha-Al2O3 and GdAlO3. With increasing the SiC content from 10 to 20 vol%, the high-temperature flexural strength of Al2O3-GdAlO3-SiC ceramics increases from 567 to 616 MPa, and the Vickers hardness increases from 17.5 to 19.5 GPa, while the fracture toughness of Al2O3-GdAlO3-SiC ceramics increases from 8.20 to 9.28 MPa m(1/2), which is significantly improved with respect to that (7.5 MPa m(1/2)) of unmodified Al2O3-GdAlO3 ceramic. The toughening mechanisms of Al2O3-GdAlO3-SiC ceramics are attributed to crack deflection, pinning and bridging, and bifurcation due to the presence of SiC nanophases observed from the indentation.