| Reaction-bonded silicon carbide ceramic, which is widely applied in high temperature valves, heat exchangers, and radiant tubes, has excellent properties of anti-oxidation, thermal shock resistance, wear resistance, high thermal conductivity, high strength, low sintering temperature and low cost. At present, parts industry is developing toward the characteristics of precision, miniaturization, complication and automation, while the traditional ceramic molding technology is difficult to conform to this trendency. Based on polymer injection molding and traditional ceramic process, ceramic injection molding technology makes it possible to form the product with near net size and complex shapes, making use of the excellent rheological properties of organic system. Due to the advantages of high automatic degree and high consistency quality in mass-production, ceramic injection moulding becomes a booming molding technology for precise ceramic components.The effects of SiC powder loading, particle size distribution, carbon black content and the ratios among the organic compositions on the feedstock rheological property and performances of body were investigated. The influnence of injection parameters, debinding and sintering process on the properties of reation-bonded SiC samples was also studied. Results indicated that the viscosity of feedstock could meet the requirements of injection molding process and the SiC body exhibited high dimensional accuracy and high strength when the ceramic powders were composed of 93 wt.% SiC (SC1:SC2=2:1) and 7 wt.% C, meanwhile, the optimal loading ceramic powder was 70 vol.%, the organic system was 30 vol.% with the composition of 60 wt.% PW,20 wt.% HDPE and 20 wt.% EVA, and SA content was 1.5 wt.% of the ceramic powder. The reasonable mixing conditions and the optimal molding parameters for the feedstock with above composition were as following:mixing time 60 min, mixing temperature 140℃, injection temperature 175℃, injection pressure 100 MPa and injection speed 5 g/cm3. The combination of solvent debinding and thermal debinding was more efficient and the optimal debinding conditions were as below. Firstly, solvent debinding was implemented in trichlorethylene at 40℃ for 6 h, and then immersed at 50℃ for 4 h. Secondly, thermal debinding was performed in N2 atmosphere and the highest temperature was 450℃. The successively sintering process was implemented in a vacuum furnace at 1720℃ for 2 h with heating rates of 1-5℃/min. The density, hardness, bending strength and fracture toughness of the reaction-bonded SiC sample reached 3.01 g/cm3,26.2 GPa,321.59 MPa and 4.16 MPa·m1/2, respectively.Then this paper studied the ceramic injection moulding process of reaction-bonded B4C/SiC composites. Results showed that the feedstock had proper viscosity, good fluidity in moulding process and high strength for green body when the loading capacity was 65 vol.%, ceramic powder consisted of 63 wt.% SiC,30 wt.%B4C (BC1:BC2=3:2) and 7 wt.% C, organic content was 35 vol.% with the composition of 60 wt.% PW, 20 wt.% HDPE and 20 wt.% EVA, SA content was 1.5 wt.% of the ceramic powders, and PVP accouted for 4 wt.‰ of the weigtht of B4C and C. The influence of B4C content on the properties of sintered was studied. As B4C contents increased from 20 wt.% to 35 wt.%, the density of reaction-bonded B4C/SiC was decreased, whereas the hardness was enhanced, the sample with density of 2.88 g/cm3, hardness of 34.3 GPa could be obtained when B4C content was 35 wt.%. The bending strength and fracture toughness of samples were increased initially and then decreased, and the bending strength and fracture toughness could be reached 308.74 MPa and 4.67 MPa·m1/2 respectively, when B4C content was 30 wt.%. Compared to reaction-bonded SiC samples, reaction-bonded B4C/SiC composite had lower density, higher hardness and toughness, which could be used as the light personal armors. |
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