| At present,the preparation of irregular ceramic parts depends on mould,which can’t realize rapid and free forming.While stereolithography additive manufacturing(SL-3D printing)has the advantages of high precision and fast forming speed.In this paper,aiming at the development of complex shaped Al2O3,ZrO2 and their related composite ceramic parts,a preparation method of high solid ceramic paste suitable for SL-3D printing process is proposed.The general idea of this paper is as follows:Firstly,the design methods and principles of polymer component,ceramic component and additive component in ceramic paste system are summarized,and the composition of each component is determined.Secondly,a new dispersing and mixing technology of UV curable ceramic paste was proposed and optimized to realize the uniform dispersion of high solid content micro and nano particles in organic polymer system.According to the UV curable and rheological properties of paste,the 3D printing process of each group of paste was optimized,and the blank with better dimensional accuracy and surface roughness was prepared.Finally,it is verified that the sintered ceramic parts have good mechanical properties and formability,and have the value of application and popularization.It can be seen that this study has a wide range of application prospects and important theoretical and practical significanceAccording to the requirements of the service performance of UV curable ceramic paste,the design principle of paste suitable for SL-3D printing was proposed.The composition and dosage of polymer,ceramic particles and additive components were analyzed,and the preparation method of each component was determined.HDDA and NPG2PODA were selected as diluent of prepolymer Di-TMPTA,and the optimized amount of initiator PI 651 was 3-4wt%of the total resin.The prediction formula of the most dense packing void ratio of composite powder particles is established,which is suitable for discrete and multi-size grading characteristics.According to the above formula,the viscosity equation and the photosensitive parameter Dp prediction equation of UV curable pastes are optimized.The method of ceramic powder modification and the amount of reagents were determined.KH560 was selected as the surface modifier,and the modification time and temperature were 90℃ and 60 min respectively.KH560-Al2O3 has a good compatibility with polymer components,and the contact angle of modified KH560-Al2O3 decreases from 35°to 19°.A kind of dispersing and mixing technology of photosensitive ceramic paste was put forward and optimized to realize the uniform dispersion of micro and nano particles with high solid content in viscous solid-liquid fluid.Filter process is used instead of drying and sieving process to avoid agglomeration after particle modification.Ethanol/Butanone azeotropic solvent was selected to reduce the viscosity of the solid-liquid mixture system,and 70℃ agitation was used to evaporate the solvent to concentrate the paste,which reduced the difficulty of particle dispersion in the organic matter and made the uniform paste.The ceramic paste with solid content of 45-50vol%,Al2O3,ZrO2,ZTA and SiCw/Al2O3 system was prepared.The polymer component was optimized to be 45vol%HDDA+55vol%Di-TMPTA,and polyethylene glycol PEG200 was selected as viscosity reducing dispersant.And the dispersant dosage was 1.2-1.8wt%of ceramic powder.The relationship between solidification thickness,line width,laser power and scanning speed of paste with different ZrO2 and SiCw contents was established,which is of great significance to optimize 3D printing process.The UV curing process and paste paving process parameters of SL-3D printing were optimized.When the scanning distance Hs is Lw/2 and the layer thickness T is between 2/5 and 3/5 of thescanning line thickness Cd,the warpage of the 3D printing greenbody can be effectively avoided.Based on the prediction formula of scanning line width and thickness of Al2O3,ZrO2 and other pastes,6-component ZTA gradient green body with length,width and height of 32×3×6 mm was prepared under the condition of 40 μm layered thickness with different laser power and scanning speed.The overall warpage of the gradient body is less than 0.1 mm,and then the optimal curing parameters of each paste are obtained.Moreover,the simulation model of flow solid coupling was established,and the distribution of paste flow field and part blank pressure field under different scraper speed and layer thickness were analyzed.Combined with the experimental verification,the optimal speed of scraper is 3.5 mm/s,which can ensure that there is no defect in the vertical plane of the billet manufacturing within the range of 25-100 μm delamination thickness.The precision of printing size and surface quality are analyzed by testing parts.The printable minimum aperture is 0.1 mm,and the corresponding size shrinkage is about 4.5%.In order to ensure the manufacturing accuracy,the SL-3D printing layer thickness is limited to 50 μm.The corresponding debinding and sintering processes were designed by analyzing the thermal decomposition temperature range of polymer components in the green body.The formability of parts is evaluated from three aspects,mechanical properties,microstructure,forming accuracy and surface quality.In view of mechanical properties,porous Al2O3 ceramics with porosity of 20.5%were sintered at 1350℃,and their bending strength and fracture toughness were 100 ± 22 MPa and 3.75 ± 0.50 MPa·m1/2,respectively.Dense ZrO2 ceramics were sintered at 1500℃,and their bending strength,fracture toughness and hardness were 754 ± 62 MPa,5.30 ± 0.80 MPa·m1/2 and 15.30±0.81 GPa,respectively.The strengthening and toughening mechanism of ZrO2 and SiCw on Al2O3 ceramics was analyzed by means of micro morphology.For example,ZrO2 can refine the particle size of the matrix,and 20vol%ZrO2 can increase the bending strength of A1203 from 410±71 MPa to 575±87 MPa at 1500℃.And at 1600℃,the fracture toughness of Al2O3 was increased from 5.5 ± 0.95 MPa·m1/2 to 6.6±0.60 MPa·m1/2 by the whisker drawing mechanism.In terms of shape accuracy,the warpage rate of ZTA parts treated at 1600℃ is lower than 0.188‰.Then in terms of surface quality,the layer thickness is less than 50 μm,and the surface roughness Ra of sintered Al2O3 ceramic core is less than 3 μm,which basically meets the surface quality requirements of the parts. |
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