and matrix combinations, such as matrices of alpha-2 and gamma-based titanium alloys with fibers of titanium diboride or titanium carbide. This has resulted in a whole new set of fiber-matrix compatibility studies and development efforts that will require considerable time to carry out.

While there are many technical challenges to be overcome for MMC applications, the economic and managerial challenges are also very significant. Some measure of the problem is provided by the following comparison: sales of titanium-matrix composites in 1989 were only a few thousand pounds, while nearly 50 million pounds of titanium and several billion pounds of aluminum were produced. Therefore, a comprehensive plan to develop the basic science and production capabilities must come from something other than natural market forces.

Conclusion: Metal-matrix commercial industrial composites have the potential for large-scale applications that require a low-cost reinforcement.

Recommendation: Fibers compatible with low-cost metal-casting processes should be developed.

The addition of fibers and whiskers to ceramic matrices can result in structural composite materials that retain the important advantages of ceramics (i.e., high-temperature resistance, environmental stability, and low density) while also overcoming the drawback of brittle behavior.

A list of some of the more prominent fibers currently available for use in ceramic matrix composites (CMCs) is given in Table 2.6. In the United States CMCs have experienced serious and concentrated development only in the past 5 years. Their application as structural materials is thus, still in its infancy. Nevertheless, CMCs have many potential performance advantages that clearly indicate that within the next decade or so they will begin to see major use.

Although the brittle nature of monolithic ceramic materials has severely limited their application, it is possible to substantially increase both strength and toughness by incorporating second-phase constituents. These properties are illustrated in Figure 2.3, which compares simple flexural test load-deflection curves for unreinforced and carbon-fiber-reinforced cement composites¹

The superior thermal stability of many ceramics relative to polymers and metals makes CMCs unique for high-temperature applications. This fact, combined with the relative low density and chemical inertness of ceramics, (see Figure 2.4) make CMCs very attractive for many potential applications.

One of the major reasons that ceramics are the largest single class of materials used, despite their brittleness, is their low cost. The prospect of

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)