Grain size effect on creep deformation of alumina-silicon carbide composites
- Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.
A study of the flexural creep response of aluminas reinforced with 10 vol% SiC whiskers was conducted at 1,200 and 1,300 C at stresses from 50 to 230 MPa in air to evaluate the effect of matrix grain size. The average matrix grain size was varied from 1.2 to 8.0 {micro}m by controlling the hot-pressing conditions. At 1,200 C, the creep resistance of alumina composites increases with an increase in matrix grain size, and the creep rate (at constant applied stress) exhibits a grain size exponent of approximately 1. The stress exponent of the creep rate at 1,200 C is approximately 2, consistent with a grain boundary sliding mechanism. On the other hand, the creep deformation rate of 1,300 C was not sensitive to the alumina grain size. This was seen to be a result of enhanced nucleation and coalescence of creep cavities and the development of macroscopic cracks as the grain size increases. Observations also indicated that the prevalent site for nucleation and growth of creep cavities in coarse-grained materials is at two-grain junctions (grain faces), whereas in fine-grained materials cavities nucleate primarily at triple-grain junctions (grain edges). Electron microscopy studies revealed that the content of any amorphous phase present at whisker-alumina interfaces is independent of alumina grain size (and hot-pressing conditions). In addition, the alumina grain boundaries are quite devoid of amorphous phase(s). This variation in amorphous phase content does not appear to be a factor in the present creep results.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 271667
- Journal Information:
- Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Journal Issue: 6 Vol. 79; ISSN 0002-7820; ISSN JACTAW
- Country of Publication:
- United States
- Language:
- English
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