Study Of Preparation, Sintering And Mechanical Properties Of Medical Zirconia Molding Body

Yttrium oxide stabilized zirconia ceramic(Y-TZP) with excellent biological biocompatibility and high transparency can take martensitic transformation through stress induced, thus, it has high mechanical properties showing an ideal dental ceramic material. However, the hardness of dense zirconia ceramic is very high, therefore hard to be machined, which has limited its further applications. At present, dental CAD / CAM(computer aided design / computer aided manufacturing) systems are adopted to manufacturing zirconia denture. At initial stage, zirconia powder was used to mold to get molding body. Then, the molding body was heated at low sintering temperature to get pre sintered body, followed by processing to get pre sintered crown. Finally, compact zirconia denture was obtained by higher sintering temperature through precise controlling the shrinkage rate. This method improves the processing efficiency of the zirconia denture, which promotes its practical application as a dental restorative material.In this paper, 3mol% yttrium oxide stabilized zirconia ceramic powder were used as raw materials, the effect of molding parameters on the properties of zirconia ceramics was analyzed by combing molding compression and cold isostatic pressing based on the formation process of zirconia ceramics. Moreover, effects of pre sintering/second sintering processes on the mechanical properties and machinability of zirconia ceramics were studied. The research results are as follows:(1) The molding parameters have great impact on the structure and properties evolution of zirconia ceramics. With the increase of molding pressure, the density of 3Y-TZP ceramics showed a significant upward trend. However, the density of zirconia ceramics increased slowly by loading to 3.5 MPa. When the holding time was over 30 s, the growth rate of the sample density was significantly reduced. But the holding time was too small. it was difficult to get an ideal ceramic body. The efficiency would decrease effectively applied by slower pressure and longer time. Therefore, the optimal molding parameters were selected as follows: the molding pressure was 3.5 MPa, and the holding time was 30 s.(2) The density of the sample can be much more improved by increasing the cold isostatic pressure, which can advance the uniformity of the ceramic powders and reduce the sintering resistance. It was found that the density of the ceramic increased slowly when the pressure was over 200 MPa, hence 200 MPa was chosen as the optimal molding pressure.(3) Effects of pre sintering temperature on physical properties, mechanical properties and machinability of the pre sintered bodies were studied. Results showed that with the increase of pre sintering temperature, the density and mechanical properties of pre sintered body were improved, however,the machinability increased at first and then decreased. When pre sintered at 1050 oC, the zirconia body has a small linear shrinkage and a good machinability after second sintered.(4) The effects of the second sintering processing on the mechanical properties, such as the linear shrinkage, density and mechanical properties of the zirconia ceramic were studied. Results indicated that with the increase of sintering temperature, the shrinkage rate and the density of the samples after second sintering temperature reached to the maximum value and remained stable. Vickers hardness, flexural strength and fracture toughness climbed to the maximum value of 12.5 GPa, 970 MPa, 5.0 MPa·m1/2 at 1500 oC, espectively. The mechanical properties of zirconia ceramics can meet the requirements of dental ceramic materials.