Threshold Stress Intensity for Crack Growth in Silicon Carbide Ceramics |
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Authors: | Bulent O. Yavuz Richard E. Tressler |
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Affiliation: | Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 |
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Abstract: | Measurements of threshold stress intensities for crack growth, K h, of three polycrystalline SiC materials were attempted using interrupted static fatigue tests at 1200°–1400°C. Weibull statistics were used to calculate conservative Kth values from test results. The K th of a chemically vapor deposited β-SiC could not be determined, as a result of its wide variations in strength. The Kth ≥ 3.3,2.2, and 1.7 MPa·m1/2 for an Al-doped sintered α-SiC; and Kth ≥ 3.1, 2.7, and 2.2 MPa·m1/2 for a hot isostatically pressed α-SiC, both at 1200°, 1300°, and 1400°C, respectively. A damage process concurrent with subcritical crack growth was apparent for the sintered SiC at 1400°C. The larger Kth 's for the HIPed SiC (compared to the sintered SiC) may be a result of enhanced viscous stress relaxation caused by the higher silica content and smaller grain size of this material. Values measured at 1300° and 1400°C were in good agreement with the Kth's predicted by a diffusive crack growth model, while the measured Kth 's were greater than the predicted ones at 1200°C. |
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