Tadashi Sasa

Potential application of ceramic matrix composites to aero-engine components

Abstract The present paper describes the potential application of ceramic matrix composites to aero-engine components by reviewing the related published papers and our experience in this field. It contains the material requirements for aero-engines, trends in aero-engine materials use, Japanese projects related to ceramic matrix composites (CMCs) and potential application of CMCs to aero-engines, such as combustors, nozzle flaps, bladed disks and others. From the point of application to aero-engines, the remaining research and development issues are discussed to some extent. Material developments, particularly of the interface and fibers for high temperature, are still required and stressed.

9.1 High-Temperature High-Strength Ceramics

This chapter discusses the developments in science and technology of high–temperature, high-strength ceramics for heat-engine applications, especially those related with silicon nitride and silicon carbide materials. The characteristics of silicon nitride and silicon carbide as high-temperature, high-strength ceramics are summarized. The application of mechanical and gas pressure during sintering is effective in increasing density and controlling the microstructure. Many ceramic materials show time-dependent mechanical behavior. Glasses are known to show subcritical crack growth (SCG) in the presence of humidity. Silicon nitrides with metal oxide additives also show SCG at elevated temperatures where the crack growth occurs along the grain boundaries. Si-based ceramics have a remarkable potential for various structural applications. The applications of structural materials to various utilizations such as heat engines require the forming technology developments of the materials to desired size and geometry as the components at high temperatures. Further improvements in the technologies and developments of newer applications are expected to precede steadily hereafter in the world of engineering ceramics.

Fabrication of Advanced C/C Composites by a Hybrid Process of CVI/Liquid Precursor Impregnation

Fabrication processing of advanced C/C composites was developed by combining the CVI and liquid impregnation-pyrolysis processes. Time-controlled temperature-gradient (TC-TG) CVI processing was developed to accelerate the carbon matrix deposition in the C-fiber preform within relatively short process-time. The temperature gradient in the perform was changed according to a controlled program. The present TC-TG-CVI process gave twice as much weight gain as that of the conventional steady TG-CVI process. The CVI process, however, showed a limitation to fill up the large pores between the bundles. Liquid impregnation-pyrolysis was, therefore, carried out after the TC-TG-CVI process to improve the infiltration of these pores. Polycarbosilane (PCS) with the yield of about 50 wt% was used as the liquid precursor to form a SiC-rich matrix to improve the oxidation-resistance. SiC matrix was observed in the pores between bundles after pyrolysis of PCS. The weight gain after pyrolysis was found to be nearly saturated after 10 cycles of the impregnation-pyrolysis process.