| Silicon nitride?Si3N4?ceramic has excellent comprehensive properties such as high hardness,good wear resistance,high temperature resistance and corrosion resistance,and have been widely used in aerospace,mechanical production and other fields.However,ceramic have high strength,high hardness and poor toughness,and it is difficult to process ceramic part with complicated structure.Additive manufacturing technology of ceramic provides a new opportunity to fabricate complex-shaped ceramic parts.In this work,the rheological properties and photocuring properties of Si3N4 slurry which is used in stereolithography,the sintering performance of Si3N4 ceramic fabricated by stereolithography and the effect of oxidation of Si3N4 powder on the photocuring properties and rheological properties of the slurry were studied.Finally,Si3N4 ceramic part with complex-shaped was fabricated by this technology.The effects of ceramic powder,powder concentration and sintering aid on the rheological properties and photocuring properties of ceramic slurry were studied.The results showed that reducing the particle size,increasing the powder concentration and increasing the concentration of sintering aid increased the viscosity of the ceramic slurry and influenced the fluidity of the slurry.The photoinitiator content influenced the critical energy dose of the slurry.When the photoinitiator content was 1.5 wt%,the lowest critical energy dose and the largest cure depth were obtained.The ceramic powder absorbed part of the light energy,thereby increasing the critical energy dose of the slurry.When the absorbance of Si3N4 powder increased from 0.229 to 0.393,the critical energy dose increased sharply from 5.42 mJ/cm2 to13.33 mJ/cm2.The ceramic powder consumed part of light energy,thereby increasing the critical exposure enrgy of Si3N4 slurry.When the solid content of the Si3N4 slurry increased from 5 vol%to 24 vol%,the penetration depth decreased from 47.37?m to 8.40?m,and the critical energy dose decreased from 14.43 mJ/cm2 to 4.99 mJ/cm2.With the solid content increasing,scattering increased and photoinitiator content decreased,resulting in a decrease in penetration depth and critical exposure energy.When the sintering aid content increased from 0 vol%to 20 vol%,the penetration depth increased from 10.40?m to 13.19?m,and the critical energy dose increased from 8.16 mJ/cm2 to 10.35 mJ/cm2.The increase of the sintering aid reduced the refractive index of the powder so that the penetration depth of the light increased,but the addition of the sintering aid increased the scattering center,resulting in an increase in the critical exposure energy.Based on the above research results,Si3N4 ceramic parts with complex-shaped were fabricated by stereolithigraphy.The sintering behavior and mechanical property of Si3N4ceramic were also studied.The effects of cold isostatic pressing and gas pressure sintering on processing Si3N4 ceramic were further studied.The results showed that as the powder concentration increased,the cracks and gaps appeared in the brown bodies and the relative density of the brown bodies was about 38%.The density of Si3N4 ceramic was 93.19%TD at1800 oC,and its hardness and fracture toughness were 13.26±0.53 GPa and 6.68±0.71MPa·m1/2,respectively.The sintering shrinkage ratio of sintered body was about 30%in all directions.After cold isostatic pressing,the relative density of the brown body was increased to 44.58%TD and the density of the sintered body was increased to 95.36%TD.The hardness and fracture toughness are 14.78±0.43 GPa and 7.73±0.51 MPa·m1/2,respectively.The relative density of Si3N4 ceramic after gas pressure sintering reached 97.84%TD,and the hardness and fracture toughness were 14.99±0.30 GPa and 7.46±0.81 MPa·m1/2,respectively.In this work,the cure depth of slurry was improved by surface oxidation of Si3N4 powder and the effects of oxidation treatment on the photocuring properties and rheological properties were also studied.The results showed that the"core-shell"structure was formed whereas Si3N4as the core and SiO2 as the shell by means of surface oxidation.The SiO2 layer on the surface of the oxidized powder can reduce the absorbance of the powder,thereby reducing the critical energy dose of the ceramic slurry.After the powder was oxidized at 1200°C for 60 min,the absorbance decreased from 0.255 to 0.207,and the critical energy dose of the slurry decreased to 7.80 mJ/cm2 to 2.76 mJ/cm2.The SiO2 layer decreased the refractive index of the Si3N4powder,thereby increasing the penetration depth of the incident light.After Si3N4 powder was oxidized at 1350°C for 60 min,and the penetration depth of the light increased from 8.04?m to 17.04?m.The cure depth of the ceramic slurry was improved by the combination of the powder absorbance and the refractive index.After the powder was oxidized at 1350°C for 60min,and the cure depth increased from 22?m to 48?m when the exposure energy was 125mJ/cm2.In addition,the oxidation treatment can effectively improve the fluidity of the Si3N4slurry,and is a feasible way for preparing Si3N4 slurry with high solid content and low viscosity. |
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