Ceramics for Aero-Engine Applications

Abstract

In the general aero-engine development effort to significantly improve specific fuel consumption as well as thrust-to-weight ratios, ceramics have been under investigation since the mid-Seventies. Their great potential for increasing gas-turbine performance has resulted in a number of research programs worldwide to assess their desirability for static or rotating components. There has been remarkable progress in the drive to improve material strength by especially process control and the clean room approach. This development has been assisted by revised design and lifing methods. Thus static components like hybrid vanes and combustor rings have withstood temperatures of up to 1650 °C for several hundred hours and some ten cycles. But for ceramics, one essential property required of all aero-engine materials — defect tolerance, or the ability to reduce stresses in a controlled manner — still falls short of the standard commonly associated with other materials. Attention is therefore focused on methods of controlling the inherently poor defect tolerance of ceramic materials by appropriate design concepts (small volumes, simple shapes, constant wall thickness, compression stress state) and by strengthening the material proper through fiber reinforcement. Apart from the ambitious application of monolithic or fibrereinforced ceramics as structural components in the hot gas path in extremely high temperature environments, some applications, such as thermal barrier coatings, bearings and flaps, have already reached the production stage.