Processing and properties of Al₂O₃/SiC nanocomposites

Abstract

high-temperature mechanical behaviour. The strength is Alumina/SiC nanocomposites were produced by mechanical mixture of commercial powders. The preparation steps involved the vigorous mixing of the powders and drying under conditions where the homogeneous mixture was kept stable. Pressureless sintering of die-pressed powders achieved reasonable densities (~9 7 % theoretical density) for 2.5wt% of Sic on sintering at 2073 K. Higher Sic contents strongly reduced the sintered density. The use of a more reactive alumina (finer matrix powder) gave similar results. Hot pressing at 19 73 K / 1 h/25 MPa produced highdensity materials for Sic contents as high as 20 wt%. Transmission and scanning electron microscopy analysis showed that the Sic particles were well distributed and were situated both inside the grains and on the grain boundaries of the alumina matrix. The Sic strongly inhibited grain growth in the matrix in keeping with the Zener model. The bend strength increased as the Sic content increased, a result partly explained by the grain size refinement. The strength improvement of 20% over monolithic was explained in terms of the change to an intergranular fracture mode.

Electron microscopy of crack/particle interactions in Al2O3/SiC nanocomposites

“…Niihara (1991) and Zhao et al (1993) have both reported an increase of about 20-40% in the toughness of alumina/ SiC nanocomposites, as measured by means of SENB (singleedge-notched-beam) and indentation-strength methods. In contrast, Borsa et al (1995) and Carroll et al (1996) found no toughness increases in similar composites by the indentation method. This may be due to the limited accuracy of the indentation method.…”

Direct evidence for compressive elastic strain at ground surfaces of nanocomposite ceramics

“…Since the first report of significant strength and toughness improvements in polycrystalline alumina by incorporating a dispersion of 5 % -10% submicron silicon carbide particles, 1 some but not all subsequent studies have shown enhanced fracture strength and all have found only small, if any, increases in fracture toughness. [2][3][4][5][6] The differences in fracture strength between the "nanocomposite" and alumina have been found to depend strongly on the surface finish of the materials. 7 Although Zhao et al 2 suggested that strengthening might result from a compressive surface residual stress introduced by the machining, the evidence for this has been limited.…”

Sintering of Al2O3–SiC composite from sol–gel method with MgO, TiO2 and Y2O3 addition

“…The addition of small volumes (5-10 vol.%) of a nano sized reinforcing SiC agent causes a significant improvement in the inherent mechanical properties of monolithic ceramics [8][9][10][11][12][13][14][15][16]. The mechanisms behind these observed improvements with these small additive volumes are not completely explained.…”