SiC Platelet-reinforced Al₂O₃ Composites by Free Sintering of Coated Inclusions


Todd, R. I.


SiC platelets were coated with a fine-grained Al2O3 precursor powder by controlled heterogeneous precipitation from solution. After calcination, the coated platelets were compacted and sintered at a constant heating rate of 5 °C min−1 in a helium atmosphere. The parameters that control the coating process and the sintering behaviour of the coated powders were investigated. For given reactant and platelet concentrations, pH and temperature, the presence of a small amount of poly(vinylpyrrolidone) (PVP) produced a more homogeneous coating which, in turn, produced an improvement in the sinterability of the coated platelets. Composites formed from the coated platelets, with an initial matrix density of 40-45% of the theoretical and containing ≈ 20 vol% platelets, reached nearly full density after sintering at 1800 °C for min. By comparison, similar composites formed by mechanical mixing of the SiC platelets and freely precipitated Al2O3 powder reached a density of only ≈ 70% of the theoretical under identical sintering conditions. The strength and fracture toughness of the sintered composites formed from the coated platelets were measured in three-point loading at room temperature. For the composite containing 20 vol% platelets, the strength and fracture toughness values were MPa and 5.4 MPa , respectively. They are comparable to the highest values reported for similar composites produced by hot-pressing of mechanically mixed systems.


Materials Science and Engineering

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Article - Journal

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© 1996 Elsevier, All rights reserved.

Publication Date

01 Jan 1996