No abstract

No abstract

No 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 SiO 2 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/cm 3 for bulk density, 45.8 MPa for cold modulus of rupture (CMOR), 57 MPa for hot modulus of rupture (HMOR).

The WC composite powder was synthesized by a new specific chemical activation technique. A large number of lattice defects such as surface humps, dislocations and stacking fault exist in the surface of the WC powder after chemical activation technique. By using such activated WC powder, the binderless WC cemented carbide with high density (15.54 g/cm3), super hardness (average 26.29 GPa) and excellent fracture toughness (8.9 MPa.m1/2) can be fabricated by SPS at 1700 °C and 50 MPa pressure. The improvement in density, hardness and fracture toughness are respectively 4.5%, 15.3% and 17.1% compared to when using the original WC powder. This improvement is because microscopic defects on the surface of the WC powder can greatly improve surface free energy of the powder, which improves the sintering activity and reduces the sintering temperature of the WC powder.