Research On The Fabrication Of Zirconia Ceramics Via Stereolithography

Ceramic materials,because of their striking performance such as good mechanical strength,high hardness,high temperature resistance,excellent wear resistance and corrosion resistance,have been widely used in many fields ranging from aerospace and medical to energy and chemical industry.Nevertheless,due to the inherent high hardness and brittleness,the machinability of ceramic materials is difficult.Ceramic parts with complex structure are mostly manufactured via colloidal processing with the aid of mold.However,owing to the long manufacturing cycle and the high cost of the complex mold,it is difficult to meet the rapid manufacturing requirements of personalized,refined,and complicated high-end products.Among all kinds of rapid prototyping technologies,stereolithography shows the advantage of high precision,and has broad application prospects.The basic process of ceramic stereolithography is to prepare slurry by mixing the ceramic powders with the photosensitive resin at first,then to selectively irradiate the surface of the slurry by controlling a laser or a projector to initiate photopolymerization of the photosensitive resin in situ for binding the ceramic powders together.Subsequently,the curing of the ceramic body is achieved layer-by-layer by moving up and down the lifting platform.The as-formed green body is then debinded and sintered to obtain a ceramic part having a complicated structure.In this study,two parts of work were carried out for the manufacturing of ZrO₂ceramics based on the SLA technology.One is the optimized preparation of zirconia ceramic slurry for stereolithography,including the dispersion of zirconia ceramic powder in photosensitive resin,and the research on the surface modification mechanism of the dispersant to the powder.It was found that the specific surface area of the powder is the most important factor affecting the viscosity of the slurry.The TZ-3YSE powder produced by Tosoh Corporation of Japan showed low specific surface area and close to spherical shape,is suitable for the preparation of slurries with high solid content and low.viscosity.The relationship between solid content and viscosity of the slurry was studied and found to be consistent with the Krieger-Dougherty model.It was found that the carbonyl and ether groups in DISPERBYK-103 can be anchored to the surface of the zirconia powder and improve the affinity of the photosensitive resin to the powder.The optimal addition amount of dispersing agent DISPERBYK-103 was 3.5 wt.%.Finally 42 vol.%ZrO₂ suspension was successfully prepared with a suitable viscosity(4.88 Pa·s at 30 s^-1)below the maximum allowable viscosity value（5 Pa·s）for stereolithography applications.The second part of the work is to explore the factors affecting the cure depth,dimensional accuracy,three-dimensional sintering shrinkage and density among stereolithography and sintering.It was found that as the exposure time prolonged,the thickness of the single curing layer increased,and the interlayer bonding force of the green body was strengthened.But the excess width in the lateral direction also increased,and the printing precision decreased.The exposure time does not affect the shrinkage and density during sintering.When the solid content of the slurry increased from 36vol.%to 44 vol.%,the growing trend can be found in cure depth.But the transverse excess width of the green body was not affected.The sintering shrinkage decreased from about 26%to about 21.5%,but the density was not affected by the solid content and is higher than 98%.As the concentration of photoinitiator increased,the cure depth increased first and then decreased,and the lateral excess width of the specimen increased.But the photoinitiator concentration does not affect the sintering shrinkage and density.With the increase of the plasticizer content,the cure depth and the lateral excess width first increased and then decreased.The plasticizer does not affect the sintering shrinkage,but it might help to increase the relative density of the sintered body to some extent.The parameters were optimized as the following:the exposure time as1.75 s,solid loading as 40 vol.%,photoinitiator concentration as 1 vol.%,and plasticizer content as 25 vol.%,respectively.