Comparison of interphase removal and oxidation embrittlement mechanisms of subcritical crack growth in SiC/SiC composites
- Pacific Northwest National Lab., Richland, WA (United States)
Ceramic matrix composites are being developed to operate at elevated temperatures and in oxidizing environments. Considerable improvements are being made in the creep resistance of SiC fibers and hence in the high-temperature properties of SiC/SiC composites; however, more needs to be known about the stability of these materials in oxidizing environments before they become widely accepted. Experimental weight loss and crack growth data supports the conclusion that O{sub 2} enhanced crack growth of SiC/SiC occurs by more than one mechanism depending on the experimental conditions. An oxidation embrittlement mechanism (OEM) operates at temperatures below about 1,073--1,223 K and at O{sub 2} pressures of 2 x 10{sup 4} Pa and above while an interface removal mechanism (IRM) operates at temperatures exceeding 1,073 K and O{sub 2} pressure of 2 x 10{sup 3} Pa and below. The OEM, as proposed by Evans et al. (1), results from the reaction of O{sub 2} with SiC to form a glass layer on the fiber. The fracture stress of the fiber is reduced if this layer is thicker than a critical value (d > d{sub c}) and the temperature is below a critical value (T < T{sub g}) such that a sharp crack can be sustained in the layer. The IRM, as proposed by Henager et al. (8), results from the oxidation of the interfacial layer and the resulting relaxation of the bridging fibers. Interphase removal contributes to the stress relaxation of the fiber that occurs by creep. IRM occurs at T > T{sub g} or d < d{sub c}. This paper summarizes the evidence for these two mechanisms and attempts to define the conditions for their operation.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- OSTI ID:
- 350080
- Report Number(s):
- CONF-980316-; TRN: IM9925%%428
- Resource Relation:
- Conference: Corrosion `98, San Diego, CA (United States), 22-27 Mar 1998; Other Information: PBD: 1998; Related Information: Is Part Of Corrosion `98: 53. annual conference and exposition, proceedings; PB: [6600] p.
- Country of Publication:
- United States
- Language:
- English
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