Chapter 31. Matrix Density Effects on the Mechanical Properties of SiC Fiber-Reinforced Silicon Nitride Matrix Properties
- John B. Wachtman Jr.
Published Online: 26 MAR 2008
Copyright © 1990 The American Ceramic Society, Inc.
A Collection of Papers Presented at the 14th Annual Conference on Composites and Advanced Ceramic Materials, Part 1 of 2: Ceramic Engineering and Science Proceedings, Volume 11, Issue 7/8
How to Cite
Bhatt, R. T. and Kiser, J. D. (1990) Matrix Density Effects on the Mechanical Properties of SiC Fiber-Reinforced Silicon Nitride Matrix Properties, in A Collection of Papers Presented at the 14th Annual Conference on Composites and Advanced Ceramic Materials, Part 1 of 2: Ceramic Engineering and Science Proceedings, Volume 11, Issue 7/8 (ed J. B. Wachtman), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470313008.ch31
- Published Online: 26 MAR 2008
- Published Print: 1 JAN 1990
Print ISBN: 9780470374924
Online ISBN: 9780470313008
- tensile strength;
The room-temperature mechanical properties were measured for SiC fiber-reinforced reaction-bonded silicon nitride composites (SiC/RBSN) of different densities. The composites consisted of ∼30 vol% uniaxically aligned 142 μm diameter SiC fibers (Textron SCS-6) in a reaction-bonded Si3N4 matrix. The composite density was varied by changing the consolidation pressure during RBSN processing and hot isostatically pressing the SiC/RBSN composites. Results indicate that as the consolidation pressure was increased from 27–138 MPa the average pore size of the nitrided composites decreased from 0.04–0.02 μm, and the composite density increased from 2.07–2.45 gm/cc. Nonetheless, these improvements resulted in only small increases in the first matrix cracking stress, primary elastic modulus, and ultimate tensile strength values of the composites. In contrast, HIP consolidation of SiC/RBSN resulted in a fully dense material whose first matrix cracking stress and elastic modulus value were ∼15% and ∼50% higher, respectively, and ultimate tensile strength values were ∼40% lower than those for unHIP'd SiC/RBSN composites. The modulus behavior for all specimens can be explained by simple rule-of-mixture theory. Also, the loss in ultimate strength for the HIP'd composites appears to be related to a degradation in fiber strength at the HIP temperature. However, the density effect on matrix fracture strength was much less than would be expected based on typical monolithic Si3N4 behavior, suggesting that composite theory is indeed operating. Possible practical implications of these observations are discussed.