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A tough SiAlON ceramic based on α-Si3N4 with a whisker-like microstructure

Nature volume 389, pages 701–704 (1997)Cite this article

Abstract

Silicon nitride (Si3N4) is a light, hard and strong engineering ceramic1,2. It can withstand harsh environments and support heavy loads at temperatures beyond those at which metals and polymers fail. It can also be manufactured reliably at a reasonable cost and in large quantities. There are two forms of silicon nitride3: α-Si3N4 and β-Si3N4. The former is harder, but only the latter is currently used in engineering applications, because only this form can be given a microstructure resembling a whisker-reinforced composite1,2,4, which gives it the necessary toughness and strength. Here we report the synthesis of a tough α-Si3N4 solid solution with this kind of microstructure. This material is 40% harder than β-Si3N4 and is equally strong and tough. Its hardness (22 GPa) is exceeded only by boron carbide and diamond (which are both brittle). These properties mean that this form of α-Si3N4 should be preferred over β-Si3N4 for all engineering applications, and it should open up new potential areas in which the ceramic can be applied.

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Figure 1: Properties of an Nd0.4Si9.9Al2.1O0.9N15.1 sample.
Figure 2: Fracture toughness ( K 1c) and hardness ( H V) of Nd0.4Si9.9Al2.1O0.9N15.1 (known as Nd-1209) samples with different amounts of α′-SiAlON; the remainder is untransformed β-Si3N4.
Figure 3: Fracture toughness ( K 1c) and amount of elongated grains of seven α′-SiAlONs stabilized by cations of different ionic radii for an overall composition of R0.4Si9.6Al2.4O1.2N14.8 (m = 1.2, n = 1.2; see text).
Figure 4: α′ phase region in the Si3N4 corner of the phase diagram of (Si, Al, R) (N, O) system at 1,95.0 °C (ref. 21).

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Acknowledgements

This work was supported by the US Air Force Office of Scientific Research.

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  1. I-Wei Chen & Anatoly Rosenflanz

    Present address: Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, Pennsylvania, 19104-6272, USA

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  1. Department of Materials Science and Engineering, University of Michigan, Ann Arbor, 48109-2136, Michigan, USA

    I-Wei Chen & Anatoly Rosenflanz

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Chen, IW., Rosenflanz, A. A tough SiAlON ceramic based on α-Si3N4 with a whisker-like microstructure. Nature 389, 701–704 (1997). https://doi.org/10.1038/39542

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