Lifetime-applied stress response in air of a SiC-based Nicalon-fiber-reinforced composite with a carbon interfacial layer: Effects of temperature (300 to 1150 C)
- Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.
The lifetimes in air as a function of applied flexure stress and temperature (300--1,150 C) are described for a Si-O-C based (Nicalon) fiber plain-weave cloth reinforced SiC-matrix composite ({approximately}7% closed porosity) with an {approximately}0.3 {micro}m thick carbon interfacial layer. The measured lifetimes of both samples with and without an external SiC seal coating were similar and decreased with applied flexural stress (for stresses greater than {approximately}90 MPa) and with temperature. At temperatures of {ge}600 C, the external CVD SiC coating had negligible effect on the lifetimes; however, at 425 C, a detectable improvement in the lifetime was observed with an external SiC coating. When the applied stress was decreased below an apparent threshold stress (e.g., {approximately}90 MPa) for tests conducted at temperatures {le}950 C, no failures were observed for times of {ge}1,000 H. Electron microscopy observations show that the interfacial carbon layer is progressively removed during tests at 425 and 600 C. In these cases, failure is associated with fiber failure and pull-out. At 950 and 1,150 C, the carbon interface layer is eliminated and replaced by a thick silica layer due to the oxidation of the Nicalon fiber and the SiC matrix. This results in embrittling the composite.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 638371
- Journal Information:
- Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Journal Issue: 7 Vol. 81; ISSN 0002-7820; ISSN JACTAW
- Country of Publication:
- United States
- Language:
- English
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