Prototype silicon nitride vanes for industrial and aircraft engines were constructed and tested. Relevant material properties were determined for hot pressed silicon nitride and silicon carbide. The capability of these ceramics was compared to vane superalloys in tests relating to high pressure and temperature gas turbine environments.
Ceramics in current favor are superior to those which failed in decades past. However, they probably need further improvement if they are to replace cooled superalloys in long life cyclic applications. In more advanced engines, cooling may be required to keep ceramic vanes within their useful temperature range.
The primary limitations revealed were a propensity for sudden thermal fatigue crack propagation and low impact damage resistance. Nonetheless, ceramics still offer great potential benefit in improving performance and efficiency. To achieve success in the use of ceramics it will be necessary to attack their limitations directly. Required work will include establishing specialized performance criteria, careful design analysis, and goal-oriented material development.