Recent advances in whisker-reinforced ceramics
- Metals and Ceramics Div., Oak Ridge National Lab., Oak Ridge, TN (US)
A complication in the application and development of ceramic materials has been their low fracture toughness/resistance as compared to metallic systems. Thus while quite high flexure strengths can be achieved in ceramics by careful processing and machining, the strengths are quite flaw size sensitive, and the materials can lose a substantial fraction of their strength because of damage introduced curing service, e.g., static load slow crack growth, cyclic fatigue, creep damage, thermal gradients and/or shock, and impact or contact damage. As a result, material design approaches are actively sought that can impart a substantial degree of roughness to ceramics. Studies conducted earlier in this decade showed that incorporating 20 vol% of very strong microscopic SiC whiskers into a fine-grained ({lt}2 {mu}m) polycrystalline alumina matrix can result in a 3-fold increase in fracture resistance. This is achieved by using SiC whiskers, which themselves have a fracture toughness of only {approx}3 MPa m{sup 1/2}; a value that is comparable to that of the fine-grained aluminas. Micromechanic models are being developed to describe the toughening response of whisker-reinforced ceramics and include the influence of material parameters so that they can be used to design advanced composites. This paper describes these whisker-reinforced composites now constitute an important new class of toughened ceramics with improved mechanical properties over a wide temperature range. The paper will first describe the mechanics of the toughening process, then the effects of material parameters on the toughness observed, and finally the improvements obtained in other mechanical properties including thermal shock, elevated temperature strength, and delayed failure and creep resistances.
- OSTI ID:
- 5481087
- Journal Information:
- Annual Review of Materials Science; (United States), Vol. 20; ISSN 0084-6600
- Country of Publication:
- United States
- Language:
- English
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