Microstructure and properties of porous CMCs prepared by HIPing the pyrolyzed ZrO2/Si/Phenol Resin composite

A novel two-step process was used to investigate the microstructure and properties of porous CMCs prepared by HIPing the pyrolyzed composites of commercially available ZrO2 (TZ-3YS), silicon powders and phenolic resin. In the first step, preforms with 70, 80 and 90 mass % of ZrO2 powders were prepared by the pyrolysis of ZrO2 / Si / Phenol Resin composites at 850 degrees C in vacuum. And, then the pyrolyzed preforms were HIPed at 1400 degrees C for 30 minutes in Argon atmosphere under a pressure of 50 MPa to fabricate the porous CMCs, in the second step. XRD analyses suggested the formation of beta-SiC in the composites below the melting point of silicon. SEM photographs showed that spherical pores of several mu m in diameter were uniformly distributed in the matrices of composites and crystals of beta-SiC with facets were observed in the pores. EDS analyses showed that the crystals were composed of Si and C with 1 : 1 atomic ratio suggesting that crystal are SiC. The maximum hardness (13.78 GPa) was achieved from the composite with 90 mass % ZrO2, which is more than that of bulk hardness of ZrO2 (10-12 GPa).