| Zirconia ceramic materials have shown good application prospects in various fields due to their excellent mechanical properties.As a kind of additive manufacturing(3D printing)technology,zirconia parts with porous structures and complicated curved surface structures can be fabricated via the DLP processing which can overcome the deficiencies of the conventional ceramic fabricating process.In this paper,the zirconia ceramics were formed by DLP processing.The DLP equipment suitable for zirconia ceramic was designed and optimized.The processes of slurry preparation,DLP processing,thermal debinding and sintering were studied and optimized.(1)In this paper,according to the high viscosity and low fluidity of ceramic slurry and based on the photosensitive resin DLP equipment,the design is improved:The slurry heating system was added;The porous platform structure was proposed;The inclined stripping system was adopted;The zirconia ceramic slurry was well flattened by a jumping scrapping system.(2)The effects of various parameters on the rheological properties of the slurry during the slurry preparation were studied.The experiment showed that when the amount of dispersant added was 2wt.%,the zirconia powder with the particle size of 200nm and the added amount of 40vol.%were selected.A slurry suitable for photocuring is obtained.During the fabrication process,heating can effectively reduce the viscosity of the slurry.In order to avoid rapid sedimentation in the slurry,the heating temperature should not exceed 60℃;(3)Based on Beer-Lambert’s law,the relationship between exposure time and exposure power on the layer thickness was studied.The exposure time suitable for zirconia slurry exposure time was 5s and the exposure power of 10mW/cm~2 were determined.Source of deviation during the process was analyzed;(4)According to the test results of TG-FTIR and the removal rule of resin binder components at each temperature stage,the debinding is divided into low temperature section(230℃-300℃),medium temperature section(300℃-500℃)and high temperature section(500℃-600℃).If debinding parameters in the low and the medium temperature sections are improperly controlled,cracks will occur.In the high temperature stage,lack of support of the binder will cause the ceramic parts to collapse.Debinding in the low temperature section is mainly caused by the melting of the low melting point binder,which is driven to the outside of the green part by the thermal expansion force.The optimum holding temperature of the stage is 267℃by the dichotomy and SEM observation.In the medium temperature section,large amount of binder removal led to cracks.The holding temperature is required to reduce the release rate of the heat to avoid transitional expansion.Combined with TG-FTIR results and process experiments,the optimum insulation holding temperature were 350℃and 440℃.According to the TG/DTG results,the holding temperature of the high temperature section was 550℃.The parts are half buried in the 0.5 mm zirconia ball to prevent the parts from collapsing due to lack of binder.The dimensional shrinkage during the debinding process was studied.The shrinkage rates in the Z direction and the XY direction were 7.50%and 7.12%,respectively.The shrinkage was mainly caused by the large removal of the binder,which mainly occurred in the medium temperature section.Sintering was carried out with optimum sintering process parameters at the sintering temperature of 1480℃and the sintering time of 3h.The toughness of the sintered part was 13.91GPa.The sintering dimensional shrinkage was 24.8%,and the bending strength of the corresponding specimen was 442.0 MPa.The parts were free of cracks and had a relatively uniform shrinkage. |
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