Abstract
Silicon carbide (SiC) ceramics show excellent performance at high temperatures. Due to the high covalence of Si-C bonds, these ceramics are produced successfully only via liquid phase sintering (LPS). In this work, SiC ceramics were sintered via LPS using eutectic mixtures of Al2O3+Y2O3, which served as a standard for comparison, Al2O3+Yb2O3 and Al2O3+Dy2O3. The oxides mixtures were used to form liquid phase during the SiC sintering. Mixtures of SiC and additives were ground, pressed at 300 MPa and sintered at 1950oC for 2 hours. All mixtures showed similar hardness, fracture toughness and flexural strength slightly different. Also the microstructure and crystalline phase were similar, showing that the ytterbium's and dysprosium's oxides can be also used as additive as well the most used oxide, yttrium oxide.
Highlights
Silicon carbide (SiC) ceramics have many applications because they allow the combination of important properties such as low density, high elastic and rupture modulus, high thermal shock resistance, and high resistance to corrosion and oxidation at high temperatures[1,2,3,4,5,6,7,8,9,10,11,12,13].One of the properties of SiC ceramics that limits many applications is their low fracture toughness
Where KIC,SEVNB is the mode I fracture toughness (MPa.m1/2) determined by the SEVNB method, F is the fracture load (MN) at the instant of rupture, B is the sample thickness, W is the height of the sample, S1 is the distance between the two rollers, α is the ratio between notch size and height of the sample, and Y is the shape factor
A comparison of the ALY, ALYB and ALD mixtures indicates that the densification of the ALD ceramics was slightly greater than the ALYB mixture, which was similar to the ALY mixture
Summary
SiC ceramics have many applications because they allow the combination of important properties such as low density, high elastic and rupture modulus, high thermal shock resistance, and high resistance to corrosion and oxidation at high temperatures[1,2,3,4,5,6,7,8,9,10,11,12,13]. Various additives have been studied for the formation of this liquid phase in order to improve sintering and promote the formation of favorable microstructures with higher fracture toughness values than the existing ones. Among the aforementioned rare earth oxides, the one best known for production of the liquid phase during sintering is Y2O3, which appears in numerous publications[1,2,3,4,5,6,7,8,9,10,11,12,13]. This article evaluates the properties of compactability, densification, rupture modulus, fracture toughness and hardness
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