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Using Microstructure to Attack the Brittle Nature of Silicon Nitride Ceramics

Published online by Cambridge University Press:  29 November 2013

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Extract

The evolution of silicon nitride ceramics over the last two decades has brought about the advancement of materials which were first fabricated by the application of mechanical pressure and temperature (i.e., hot pressing) resulting in high flexure strengths (e.g., 700–800 MPa) but rather poor resistance to creep at temperatures of ~1200°C. At the same time, these ceramics remained quite brittle with fracture-toughness values of 4–5 MPa m½, such that strengths were very sensitive to flaw or crack sizes. As a result, measured strengths exhibited considerable scatter, as reflected by a low Weibull modulus. In the ensuing years, approaches were sought to develop more economical methods of fabricating silicon nitride components by densifying to near-net shape. Methods were also sought for increasing the elevated-temperature reliability by minimizing the additives employed to promote densification and by utilizing additives that produced more stable and refractory grain boundary phases. The application of gas-pressure sintering methods, utilizing gaseous environments of 10–100 atmospheres, led to the ability to produce dense near-net shaped components with very high fracture strengths (e.g., ≥1000 MPa). At the same time, advances in processing and additive chemistry, sometimes combined with additional fabrication methods (e.g., hot isostatic pressing), have resulted in ceramics with excellent creep resistances at temperatures in excess of 1300°C. Some of these silicon nitride ceramics exceed the elevated-temperature capability of superalloys by 200°C. The initial desire for light-weight ceramic components that could sustain tensile loads for high-temperature applications is, indeed, beginning to bear fruit. One of the most impressive examples of the development of a complexly shaped lightweight component is the silicon nitride turbocharger rotor used in a number of Japanese automobiles, which is currently manufactured at a cost approaching that of the opposing superalloy rotor and provides exceptionally high mechanical reliability and production yields. Currently, there are also earnest efforts to incorporate silicon nitride valves for engines, as well as in a variety of other components (e.g., combustion swirl chambers, valve-lifter pads, etc.). The acceptance and use of this class of brittle materials, which were once considered prohibitively expensive for fabrication into complex shapes and not suited for such applications, is a remarkable testimony of the progress that has been made.

Type
Silicon-Based Ceramics
Copyright
Copyright © Materials Research Society 1995

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References

1.Lange, F.F., J. Am. Ceram. Soc. 62 (7–8) (1979) p. 428.CrossRefGoogle Scholar
2.Himsolt, G., Knoch, H., Huebner, H., and Kleinlein, F.W., J. Am. Ceram. Soc. 62 (1) p. 29.CrossRefGoogle Scholar
3.Becher, P.F. and Wei, G.C., J. Am. Ceram. Soc. 67 (12) (1984) p. C267.CrossRefGoogle Scholar
4.Becher, P.F. and Hsueh, C-H., “The Influence of Reinforcement Content and Diameter on the R-Curve Response in SiC Whisker-Reinforced Alumina,” submitted to J. Am. Ceram. Soc.Google Scholar
5.Becher, P.F., J. Am. Ceram. Soc. 74 (2) (1991) p. 255.CrossRefGoogle Scholar
6.Li, C.W. and Yamanis, J., Ceram. Eng. Sci. Proc. 10 (7–8) (1989) p. 632.CrossRefGoogle Scholar
7.Kawashima, T., Okamoto, H., Yamamoto, H., and Kitamura, A., J. Ceram. Soc. Jpn. 99 (1991) p. 1.CrossRefGoogle Scholar
8.Mitomo, M., in Proc. 1st Int. Symp. Sci. Eng. Ceram., edited by Kimura, S. and Niihara, K. (Ceramic Society of Japan, Tokyo, 1991) p. 101.Google Scholar
9.Han, S-M. and Kang, S-J.L., this issue.Google Scholar
10.Mitomo, M. and Hirosaki, N., this issue.Google Scholar
11.He, M.Y. and Hutchinson, J.W., Int. J. Solids Struct 25 (9) (1989) p. 1053.Google Scholar
12.Becher, P.F., Hwang, S-L., Lin, H.T., and Tiegs, T.N., in Tailoring of Mechanical Properties of Si3N4 Ceramics, edited by Hoffmann, M.J. and Petzow, G. (NATO ASI Series, Kluwer Academic Publishers, Dordrecht, 1994) p. 87.CrossRefGoogle Scholar
13.Krämer, M., Hoffmann, M.J., and Petzow, G., J. Am. Ceram. Soc. 76 (11) (1993) p. 2778.CrossRefGoogle Scholar
14.Peterson, I.M. and Tien, T-Y., “Effect of Grain Boundary Thermal Expansion Coefficient on Fracture Toughness of Silicon Nitride,” J. Am. Ceram. Soc., submitted.Google Scholar
15.Hoffmann, M.J., in Reference 12, p. 59.Google Scholar
16.Tajima, Y. and Urashima, K., in Reference 12, p. 101.Google Scholar