HIGH-TEMPERATURE REACTIONS OF C/C-SiC COMPOSITES WITH PRECURSOR-DERIVED CERAMIC COATINGS

摘要

The dip-coating process with boron-containing organosilicon polymers and the subsequent thermolysis allows the production of protective ceramic coatings, e.g., for carbon fiber-reinforced composites. In order to avoid cracking of the coatings, active (titanium), inert (SiC), or a mixture of inert and active (SiC and silicon) fillers are applied. The CALPHAD (CALculation of PHAse Diagrams) method is used to determine the phase equilibria of the derived ceramics in the Si-B-C-N system and their reaction with filler materials during processing and high temperature application. Phase fraction diagrams for the various ceramics and for the filler-free polymer-derived ceramic are presented and compared with experimental results. The combination of thermodynamic calculations and experimental investigations simplifies a proper selection of starting materials. Scanning Electron Microscopy images of the coatings prepared by the method designated earlier are shown. Reentry simulations of coated C/C-SiC specimens are carried out in a low-pressure atmosphere of airlike composition in a plasma wind tunnel test facility.