The Research Of Two-Step Sintering And Selective Laser Sintering Froming Of Alumina Ceramics

Two-step sintering is an effective method for preparing high-performance Al₂O₃ ceramic materials.It has a significantly advantage in reducing the sintering temperature,controling the grain size,enhancing the density and improving the microstructure. Selective laser sintering process,a moldless and near-net-shaping method for any type of shape,can be used to make the manufacture processing of Al₂O₃ more easily.In this paper,high purity Al₂O₃ is used as raw material,and the Al₂O₃ceramic body is obtained by the two step forming process combined with compression molding and cold isostatic pressing?CIP?.Sintering is done by two step sintering process.That is to say, firstly,the green body is preliminarily sintered under the conditions of normal pressure and temperature range of 1400°C-1500°C,then treat the pre-sintered body with hot isostatic pressing?HIP?at a pressure of 120MPa and a temperature range of 1250°C-1350°C.The mechanical properties and microstructure of Al₂O₃ ceramic were tested and analyzed.The influence of process parameters on the flexural strength and fracture toughness of Al₂O₃ceramic in two-step sintering was analyzed by variance analysis.The results showed that the three main process parameters influencing the mechanical properties of ceramics were as followed:the normal pressure sintering temperature,the HIP post-treatment temperature and the atmospheric pressure holding time.The two-step sintering method could be used to prepare dense and fine-grained Al₂O₃ ceramics with comprehensive properties.The optimal program of two-step sintering process of Al₂O₃ ceramic is to sinter the ceramics at1450?for 1.5h in atmospheric followed with HIP processing at 1350?for 1h under the pressure of 120MPa.After processed at the above condition,Al₂O₃ ceramics with grain size of 1.2-1.7?m were obtained,of which the flexural strength is 637MPa,the hardness is2133HV10,and the fracture toughness is 5.27MPa·m^1/2.The mixed powders of epoxy resin E12 and spray granulating Al₂O₃ ceramic powder were used to form Al₂O₃ ceramic body by the selective laser sintering?SLS?process.The shape of the Al₂O₃/EP can be gotten body accuracily if the range of laser energy density varies between 0.171J/mm³ and 0.102J/mm³.The subsequent cold isostatic pressing?CIP?on the SLS formed Al₂O₃ ceramic body can improve the sintering process of the green body.The optimal processed concedure included CIP after SLS,following the removal of forming agent and secondary CIP process.Based on the experimental results above,the artificial acetabulum composed of dense Al₂O₃ ceramics with fine grain was successfully prepared by SLS multi-step forming process and the two-step sintering process.the acquaintable density was 3.927g/cm³?The results of EDS and XRD analysis revealed that silicon-based inorganic filler existed in the commercially available epoxy resins used for SLS forming in this paper,made the obvious difference in microstructure and densification of the sample shaped by SLS compared with the processing by molding.