Effect of Soaking Time and Molding Pressure on in-situ Synthesis of β-SiC Whiskers in Reaction-bonded SiC Ceramics

Abstract

To enhance the high-temperature strength of SiC ceramics, β-SiC nanowhiskers were successfully in-situ synthesized to bond with α-SiC aggregates by using a reaction-bonded sintering method, and the effects of soaking time and molding pressure on the in-situ synthesis of β-SiC nanowhiskers were studied. The optimized processing parameters were obtained from the aspects of whisker morphology and properties. The results showed that short soaking time of < 2 h resulted in the insufficient carbothermal reduction of SiO₂ and the low partial pressure of SiO gas, which suppressed the growth of β-SiC whiskers. Excess soaking time of > 2 h led to the active oxidation of the SiC aggregates and the seriously loosened structure. The density as the result of molding pressure had significant influences on the features of β-SiC whiskers, and the yield of SiC whiskers decreased with the increasing molding pressure. When the soaking time and molding pressure were set as 2 h and 20 MPa, respectively, the obtained SiC whiskers exhibited the highest aspect ratio of 130 ~ 200 and the as-prepared sample possessed the optimal properties: 17.5% for porosity, 2.46 g/cm³ for bulk density, 45.8 MPa for cold modulus of rupture (CMOR), 57 MPa for hot modulus of rupture (HMOR).