Fiber coatings for brittle matrix composites. Ph.D. Thesis
The current interest in tough, high-temperature materials has motivated fiber coatings development for ceramic matrix composites. Such coatings are needed for controlled interface debonding and frictional sliding. The composite investigated in this study was sapphire fiber-reinforced alumina. This system is thermochemically stable for severe use conditions, exhibits little thermal expansion mismatch, and utilizes the excellent strength and creep resistance of sapphire reinforcements. A variety of coating materials was investigated with respect to their ability to satisfy thermochemical and thermomechanical properties criteria as needed for toughness improvement. Few suitable materials were found. The most promising coatings included porous oxides, a few refractory metals, and carbon. These were identified by employing a variety of analytical and mechanical testing techniques to determine the interface chemistry and structure as well as the interfacial fracture energy and sliding resistance. The results indicate that the interfacial properties can be controlled with coatings which can be eliminated from the interface subsequent to composite consolidation. However, these fugitive coatings also contribute to the high temperature strength degradation of sapphire fibers. Such degradation can be minimized by selecting appropriate composite processing conditions, but overcoming fiber strength loss remains an important issue for the use of these composites.
- Research Organization:
- California Univ., Santa Barbara, CA (United States)
- OSTI ID:
- 121805
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: 1993
- Country of Publication:
- United States
- Language:
- English
Similar Records
Fiber coating concepts for brittle-matrix composites
Whisker-reinforced ceramic matrix composites with modified interfaces. Ph.D. Thesis