Microstructure and Properties of Porous CMCs Prepared by HIPing the Pyrolyzed ZrO₂/ Si / Phenol Resin Composite

Abstract

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 oC in vacuum. And, then the pyrolyzed preforms were HIPed at 1400 oC 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 β-SiC in the composites below the melting point of silicon. SEM photographs showed that spherical pores of several μm in diameter were uniformly distributed in the matrices of composites and crystals of β-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).