Optimization of a pyrolysis procedure for obtaining SiC-SiCf CMC by PIP for thermostructural applications

For most thermostructural applications, fragility of ceramics is a major disadvantage, so fiber-reinforced ceramics, with higher fracture toughness and pseudoplastic behaviour, need to be developed. Polymer Impregnation Pyrolysis (PIP) is a cost effective technique for obtaining SiC-fiber-reinforced Ceramic Matrix Composites (CMC). A commercial UBE polymeric precursor of a SiC ceramic matrix was used to infiltrate SiC felts, applying different pyrolysis procedures. In particular, pyrolysis was performed in two conditions: at 1000 °C for 60 min and at 900 °C for 120 min. A pyrolysis at 900 °C could be more convenient since it can be easily performed in a steel furnace. Thermogravimetric TG-DTA analysis were used to establish pyrolysis efficiency and pyrolysis temperature, and XRD to investigate ceramic phase formation and phase purity. SEM-VP was used to study morphology and microstructure of the CMCs. There were not unfavorable consequences of a pyrolysis temperature of 900°C, but the relative density and the mechanical properties of the produced CMC were lower than the expected, probably because of the procedure of vacuum impregnation adopted and because of matrix microcracking induced by a too high pyrolysis rate.