Oxide CMC Components Manufactured via PIP Processing Based on Polysiloxanes

Abstract

For a long time polysiloxanes have been used to build up an oxidation and corrosion resistant matrix (SiOC) in damage tolerant ceramic matrix composites (CMC) using polymer infiltration and pyrolysis (PIP) processing. These oxide CMCs are reliable candidates for aeronautics applications, such as turbine inlets for future jet engines. Another interesting feature of these materials is the transparency for radar waves in front structures of air vehicles (e.g. radomes). State of the art is the infiltration of fibre preforms with polysiloxanes and pressure less curing. At DLR, pressure-assisted infiltration and curing via resin transfer moulding (RTM) as well as warm-press technique was developed further in order to use systems curing via polycondensation. In a second process step, the pyrolysis, the “dense” polymer matrix is transferred into a porous ceramic matrix due to shrinkage. Further densification of the matrix to an open porosity < 10 vol-% can be efficiently performed by RTM route or near-vacuum infiltration in a resin bath. In this contribution the variety of manufacturing methods of oxide CMC components based on OXIPOL (oxide CMC based on polymers) is described. Therefore, oxide fibres (Nitivy or Nextel) and commercial polysiloxanes were chosen. In order to obtain high damage tolerance, based on weak fibre/matrix bonding, a fugitive coating was used. Therefore, a phenolic resin solution was applied on fabrics with a Foulard machine prior to composite manufacture. After the last pyrolysis step the carbon (ex-phenolic resin layer) on the fabrics was removed via oxidation at 700 °C in air for 20 h. Depending on the design and application needs of the component, several industrial processes, such as RTM, pressing of fibre performs as well as wet filament winding of rovings, were applied. Moreover, different kind of fibre types, fibre orientation, liquid or solid polymers and coating thicknesses were used. In addition, some first application tests are presented.