Applications of CMCs Made via the Liquid Silicon Infiltration (LSI) Technique

Abstract

IntroductionFibre reinforced ceramics can be defined as composite materials, which on the one hand demonstrate the typical material characteristics of high temperature ceramics, and on the other open up the technical manufacturing possibilities for the construction of large, thin walled, complex structures feasible with polymer based composites. Ceramic matrix composites (CMC) are very promising materials for use in structural applications when one considers their low mass (~ 2 g/cm 3 ), excellent thermal shock stability and strength at high temperatures. Different processing techniques are currently in use for the manufacture of complex shaped CMC components based on a fibre architecture of continuous carbon or silicon carbide fibres. A novel technology to produce CMC structures with lower costs and shorter manufacturing times has been developed at DLR [1]. The Liquid Silicon Infiltration (LSI) process is based on the infiltration of economically manufactured carbon / carbon with molten silicon and leads to so-called C/C-SiC materials. The LSI process allows the fabrication of thin walled, extremely lightweight C/C-SiC structures. It is a three step process starting with carbon fibre reinforced polymer (CFRP) manufacture followed by carbonization and concluding with liquid silicon infiltration. The advantage of the LSI process is that it is a near net shape process without reinfiltration steps. Moreover, the LSI process enables the joining of substructures in-situ. An homogeneous, and therefore strong, joint can be produced by implementing molten silicon as a joining material which reacts with carbon, either from the joining specimen or introduced as a paste to the joining surfaces, to form silicon carbide so the joint is as strong and thermally stable as the basis C/C-SiC material.The typical field of application for CMC lies where metals, or superalloys, due to their insufficient mechanical strength at elevated temperatures, can no longer be considered and encompasses all areas of lightweight construction. Thus, all projects concerning future space transportation systems and hypersonic aircraft foresee the extensive use of these materials, in particular for engine intake flaps, nozzles, thermal protection systems (TPS) or so-called hot, load bearing structures in the wings and fuselage, in order to fulfill the extreme lightweight construction demands. However, if the application is in an oxidising atmosphere carbon burnout of both the fibres and the matrix will start at temperatures as low as 450 °C. For these applications, carbon based CMCs can only be utilised for a limited lifetime. Even oxidation protective coatings will only reduce material degradation rather than to prevent oxidation completely.This paper discusses the LSI process and presents examples of CMC applications. Successful applications for the high temperature regime are space reentry structures. Commercially attractive applications within the medium temperature regime take advantage of the excellent High Temperature Ceramic Matrix Composites....

Creep of monolithic and fibre-reinforced silicon carbide

“…38,39 However, if SiC fibre reinforcement is preferred, a study has been made of the room temperature mechanical properties of four BN/SiC-coated SiC fibre performs before and after different time-temperature exposures in 0.1 MPa argon atmospheres. 40 The four types of SiC fibre were Hi-Nicalon TM and Hi-Nicalon-S TM from Nippon Carbon Co., as well as Sylramic TM from the Dow Corning Co. and in situ BN-coated Sylramic TM produced by a NASA process.…”

High temperature C/C–SiC composite by liquid silicon infiltration: a literature review

“…TPS panel is one of the crucial elements for space application (Kochendorfer and Lutzenburger 2001;Krenkel et al 2004). It needs to have low mass and high temperature stability along with low coefficient of expansion.…”

“…The C/C-SiC composites have all these properties. Some of the components for the heat exchangers are given in figure 21 (Kochendorfer and Lutzenburger 2001).…”

“…Also, the optical system has high demand on precision and stability. Figure 22 shows some of the high precision components, which are made of C/C-SiC composites (Kochendorfer and Lutzenburger 2001).…”

“…(a) Thermal protection systems and (b) threaded fastener of C/C-SiC composite(Kochendorfer et al 2001;Krenkel 2004).…”