density values, may provide useful properties for special applications. Other processes are expected to be discovered or exploited as the markets for high-performance synthetic fibers evolve.

As composite material systems become increasingly sophisticated to meet ever-increasing performance requirements, it has become necessary to develop more advanced methods for controlling the manner in which the reinforcing fibers interact with the matrix material. This is especially important in the ongoing efforts to develop high-strength, damage-tolerant ceramic-matrix composite materials⁵⁴ that have higher-temperature capabilities, such as for use in high-temperature regions of turbine engines. Since there are a limited number of available types of fibers that have the requisite properties for high-temperature applications, it has become necessary to develop coatings and surface treatments that facilitate the use of these fibers in an ever-widening selection of matrix systems. The application of a coating to the fiber surface is one of the most versatile methods^55,56 for controlling the fiber-matrix interaction. Other methods include providing additional elements to the matrix that will either form precipitates that segregate at or react with the fiber surface during fabrication and in situ modification of the fiber surface during fiber manufacturing. In this section fiber coatings will be emphasized.

Coatings offer the possibility of tailoring the fiber-matrix interfacial properties so that optimum composite properties can be achieved. Fiber coatings can have a profound effect on the composite material at all stages of its existence from fabrication to in-service use. Fiber coatings perform the following general functions:

• Control fiber-matrix bond strength.

• Improve strength by reduction of surface stress concentrations.

• Alter the wettability of fibers by the matrix.

• Improve the chemical compatibility with the matrix.

• Provide diffusion barriers.

• Protect fibers from damage during consolidation and fabrication.

• Protect the fiber and fiber-matrix interface from environmental degradation during service.

There are many different methods for applying coatings to fibers. The most frequently used techniques include electrodeposition, CVD, metallorganic coating, polymer precursor coating, and line-of-sight vacuum deposition techniques. Each of these coating methods is discussed in the next section.

Front Matter (R1-R16)

Executive Summary, Conclusions, and Recommendations (1-8)

1 High-Performance Synthetic Fibers for Composites (9-20)

2 High-Performance Fiber Materials: Applications, Needs, and Opportunities (21-48)

3 Fiber-Forming Processes: Current and Potential Methods (49-102)

4 Important Issues in Fiber Science/Technology (103-108)

5 Important Policy Issues (109-118)

Glossary of Terms (119-126)

Appendix (127-129)