Ceramic fibers development issues

Continuous-length ceramic fibers used to reinforce CMCs must have optimal mechanical, physical, and chemical properties (described in Chapter 2). This chapter reviews the characteristics of fibers that are commercially available and fibers that are at an advanced stage of development. The performance characteristics of interest include stiffness (i.e.. Young s modulus), strength, thermal and electrical conductivity, creep and rupture resistance, oxidation resistance, all as a function of temperature, and strength and stiffness retention as a fimetion of serviee history. The critical issue of chemical compatibility with prospective interface coatings and the eeramie matrix is addressed in Chapter 4 and Chapter 6. 

Elevated temperature applications require materials that can maintain good mechanical properties such as strength and hardness. Ceramics have good mechanical properties at high temperature and, thus, appear to be good candidates for elevated temperature applications. However, due to their brittle nature, monolithic ceramics are unsuitable for many applications where reliability is a critical issue. In the last few years, a new class of ceramic materials has been developed and studied. It is understood that two brittle materials can show non-brittle behavior if they are properly mixed. Fiber-reinforced ceramic matrix composites (CMCs) exhibit pseudo-plastic behavior at room temperature, as well as in an elevated temperature environment. Since the fiber and the matrix are made of ceramic material, creep behavior and hazardous emissions are reduced considerably. 

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