Influence of pyrolysis and Silicon infiltration on the properties of CMC parts shaped by composite flow molding

Abstract This paper investigates the influence of thermal process parameters on the mechanical properties and final microstructure of SiC‐based ceramic matrix composites parts shaped by composite flow molding, and converted into ceramics by pyrolysis and reactive silicon melt infiltration. Green composite parts consisted of a thermoplastic matrix (PEEK) reinforced with continuous carbon fibers. Parts were pyrolyzed between 960°C and 2000°C and subsequently Si infiltrated between 1600°C and 1800°C, with a dwell time of 1 to 3 h. An experimental plan was defined following a design of experiment (DOE) approach. At high pyrolysis and infiltration temperatures, samples show higher modulus of rupture (280 MPa) and flexural modulus (158 GPa). A qualitative image analysis was adopted to estimate the CMC composition. A predictive model allowing the estimation of the composite toughness as a function of the significant process parameters was derived by applying the DOE methodology and the analysis of variances. The model is based on the observed correlations between the process parameters and their influence on the material property of interest. The most influential parameters are the silicon infiltration temperature and the dwell time. This is due to their control over the reaction kinetics between C and Si to obtain SiC.