Study On The Fabrication Of Sic Structural Ceramics Parts With Large Size

SiC structural ceramic parts with large size were urgent required in many special operating conditions. So, considering the industry requirement, we carried out our studies based on an exemplification of SiC impeller with large size and complex shape, which is expected to be used in the special centrifugal pump for corrosive liquid and slurry. The main research works for the disseration focused on the follow three aspects:Granulation were adopted for the first time in gelcasting process to fabricate pressureless-sintering SiC. Granulations enlarged average particle sizes from0.51μm of raw SMP to40μm and8.2μm of compact granulated powders and spray granulated powders. The granulated powders in slurry decreased the viscosity of the slurry. Respectively, the viscosities of slurry prepared from spray-granulated powders and compact-granulated powders were1/2.5and1/3.5to that from submicron powder at a shear rate of100s-1due to the increased particle size, and the former slurry viscosity was58mPa·s-1higher than the later for the hollow particle structure. The lower viscosities benefited to leaded to a dense microstructure and bending strengths in green and sintered bodies. The bending strengths of spray-granulated powders and compact-granulated powders green bodies were approximately3times and3.5times to that of submicron powder respectively. The granulated particles were observed in the green body but disappeared during the sintering process, leading to a homogeneous microstructure and performances of sintered body; the bending strengths of spray-granulated powders and compact-granulated powders sintered bodies were approximately2.2times to that of submicron powder.Solid-phase-sintered SiC-based composites with short carbon fibers (Csf/SiC) were prepared by gelcasting. The relative densities of Csf/SiC composites decreased with increasing Csf content, while the bending strength and fracture toughness first increased and then decreased with increasing Csf content. In the case of the composite containing5.0wt%Csf, the bending strength reached its maximum value of420MPa, which was80MPa greater than that of pure SiC and30MPa greater than that of the composite by colding pressing containing the same amount of Csf. In the case of the composite containing7.5wt%Csf, the fracture toughness reached its maximum value of4.61MPa·m1/2, which was0.88MPa·m1/2greater than that of pure SiC and0.88MPa·m1/2greater than the maximum value of composite by colding pressing containing5.0wt%Csf. The main strengthening and toughening mechanisms were pull-out and frature of Csf occurred in the composite, the pyrocarbon, derived from the organics in gelcasting, wrapped around the Csf benefited to the strengthening and toughening effects.CsffSiC impeller green body were prepared by gelcasting with low viscosity slurry from spray-granulated powders, reasonable mold was designed by the optimized structural feature of impeller. Cracks during drying were hindered by balanced stress states design and drying process with controled humidity and temperature. While proper supports and temperature field control overcomed the distortion in sintering period. Final the Csf/SiC impeller with complex shape and large size upto160mm in diameter were fabricated, The relative density of the impeller was96%with a minor variation not more than0.5%and a good bending strength upto420MPa. Furthermore, this ceramics impeller displayed a lower wear rate as be expected, which was only1/10of the wear rate of the ultra-high-molecular-weight polyethylene (UHMWPE) impeller. So far, It has not yet been reported about this ceramics imeller with solid-sintered SiC.