readily justified for rather modest increases in temperature capability. But cost alone has not kept ceramic fibers or CMCs from entering the market. Significant efforts must still be directed towards increasing the performance capabilities of these materials. The following guidelines can help reduce development and manufacturing costs.

Using capital non-intensive equipment for fiber production will lower fixed costs, thus lowering cost per unit. Processes that leverage past investments can further reduce fixed costs. The development and use of less expensive fiber precursors also offer a potential reduction in variable costs. Finally, because applying coatings to fibers via CVD adds considerably to the final cost of CMCs, liquid precursor coatings or coatings developed on the fiber in-situ (without a separate processing step) can also lower costs.

Recommendation 5. Efforts to reduce the costs of fiber and coating processing should be directed toward using capital non-intensive equipment; developing less expensive fiber precursors; using processes that leverage past investments; and developing in-situ and liquid precursor coatings.

A broader, more stable vendor base for fibers and coatings could probably be established if costs could be reduced. Lower costs for fibers and coatings would make CMCs more attractive to a larger variety of end-users.

The five recommendations above fall into three categories. Recommendation 1 addresses increasing confidence in existing CMC technology. By providing engineering designers with the information they need to make materials selection decisions, it is anticipated that applications for CMCs will increase. Thus the committee places a high priority on this recommendation.

Recommendations 2, 3, and 4 fall into the second category, performance. As a group, these recommendations, which are also considered to be of high priority, are listed in the order of decreasing priority. The committee found that fiber coatings and other interface technologies for both non-oxide and oxide systems are the major technical limitation to CMC development. That is, improved fiber coatings are needed to enable CMCs to meet the higher temperature performance requirements for many applications. Recommendation 2 has the highest priority in this category because even though the oxidation resistance of oxide fibers is attractive the creep resistance of these fibers must be improved. Recommendation 3 addresses this priority. Recommendation 4 (regarding non-oxide fibers) has a lower priority because for many applications adequate properties have already been attained in non-oxide fibers. Therefore, the committee concluded that resources directed toward improving the properties of fiber coatings, and oxide fibers was more important. However, the committee is satisfied that the preliminary properties reported for Si-B-N-C amorphous fibers are sufficiently attractive to stimulate the work needed to verify them.

Although cost is an important issue, Recommendation 5 is considered lower in priority. The committee concluded that at the current stage of technology performance rather than costs have limited many CMC applications, making improved properties a higher priority than lower costs.

Front Matter (R1-R16)

Executive Summary (1-5)

1 Introduction (6-11)

2 Current and Future Needs (12-19)

3 State of the Art in Ceramic Fiber Performance (20-36)

4 Ceramic Fiber Processing (37-48)

5 Materials and Microstructures (49-53)

6 Interfacial Coatings (54-74)

7 Cost Issues (75-82)

8 Recommendations and Future Directions (83-86)

References (87-92)

Biographical Sketches of Committee Members (93-95)