| Bioceramic materials, which can be applied in producing dental implants, crowns, artificial joints, heart valves, performs very well both mechanical properties under compression and biocompatibility in the human body. Bioceramic materials characteristic is that can maintain a long time physical and chemical stability properties:not or only slight corrosion, degradation and other chemical and biochemical reactions. So in recent years the biocomposite ceramic materials reseach becomes one of the most active directions. However, ceramic material is brittle, hard to processing and poor reliability and reproducibility. Traditional sintering method only can work out a standard simple geometric shape compound biological ceramic products and cannot meet the personalized needs as medical materials so as to greatly limit its clinical application. This paper studied the experimental of composite biological ceramic on the basis of the selective laser sintering technology.The specific introductions are:(1) Raw materials were prepared and the best milling time and the sintering powders mechanism were studied. Four different ratios of Al2O3/ZrO2/SiO2 powder as raw material was mixed by using high-energy ball mill. The balling time influenced on the grain size and phase transition induced by different ball milling time was discussed. Through the analysis of microstructure and X-ray diffraction(XRD), the best time was 6h and no reunion,0.8um～1um particle size, nearly spherical Al2O3/ZrO2/SiO2 particles were obtained. The powders after ballmilling were prepared for a foundation for excellent performance complex biological ceramic layer. At the same time according to SLS mechanism studing intering driving force and the powder with the laser action mechanism can get the relationship between laser processing parameters and temperature, the powders surface temperature rised on inversely to laser scanning speed v1/2.(2) The research was focused on the forming ceramic layers without any binders and post-processing. The laser processing parameters played an important role in the ceramic layer quality. Nd:YAG selective laser sintering system was built based on homemading powders feeding equipment. It was first time to form ceramic layer which had less porosity and density of 3.72gcm-3 without adding binders and any postprocessing. By using SEM, XRD the composition, microstructures and microareas were analysed and the main processing parameters influenced on the laser sintering quality were also discussed. A better range of scanning speed and laser power achieved, laser power 40W, scanning speed 15～25 mm/s, laser power 20W, scanning speed 5-25mm/s. According to the orthogonal experiment, the results showed the influence and relationship between main process parameters and ceramic layers surface morphology:scanning speed> amount of overlap> laser power, and the best sintering condition was:scanning speed 15mm/s, laser power 40W, amount of overlap 0.4mm. The causes of spheroidizing were analysed on the grounds of spheroidization mechanism by studying the influence of scanning speed. The balling phenomenon can be avoided when the scanning speed greater than or equal to 15 mm/s.(3) Different ratios composit creamic layers surface, the fracture microstructures and mircoareas point and surface energy spectrum was studied. By using Nd:YAG laser selective sintering system, four ratios ceramic layers were formed. By SEM, XRD, EDS, Mapping and other testing means, and in analysis four ratios ceramic layers surface, the fracture surface micro structure, point and surface in mirco-areas and in comparison to four ratios ceramic layer’s microstructure, phase structure, and internal material distribution status, the best proportion can be got that was ASZ3:40%Al2O3,30%ZrO2 and 30%SiO2 (wt%). ASZ3 ceramic layer was more smooth and dense than the other ceramic layers. ASZ3 had uniform element distribution with less cracks and fractures along crystal small cracks suppressed the main cracks extension which improved the fracture toughness of ceramic layers. By studying the different proportions SiO2 influenced on ceramic layers, appropriate proportion of glass phase SiO2 can combine large, fine crystal and form eutectic mullite with A12O3, which improved the performance of the composite biological ceramic layers.(4) Three-dimensional temperature continuously moving temperature field finite element model for analyzing the single-pass and multi-pass sintering powders temperature field was systematically established. CO2 selective laser sintering system in the SLS process the temperature field and the thermal stress field were simulated based on ANSYS. During the selective laser sintering process the law of temperature varied with time was obtained. By means of orthogonal experimental design method, ceramic layers sizes were obtained from indirect selective laser sintering temperature field numerical simulation. In comprison of test results and numerical simulation results, the average errors of the sintering width and depth were 5.19% and 0.39% respectively. This verified the validity of the numerical simulation and provided the process of selective laser sintering temperature field analysis method. Stress field and residual stress in the SLS process were analyzed, and the law of stress variation with the time in the SLS stress field during the cooling process. In view of the ceramic layer crack formation mechanism, the influence factor of crack formation was analyzed and the preventing methods of ceramic layer crack were proposed.(5) The optimal sintering condition and the optimal formula of composite biological ceramic were studied by using selective laser sintering system. Four ratios biological composite ceramic layers were formed according to selective laser sintering technology. By analyzing microstructure and X-ray diffraction (XRD), main SLS processing parameters influenced on the ASZ3 ceramic layer microhardness was studied and the optimum sintering condition was sured:laser power 1000W, the scanning speed 400mm/min and amount of overlap 0.6mm. With this conditon it can be achieved the highest microhardness value. In comparison with ASZO, ASZ1 and ASZ3 microstructures and phase constitutions, microhardness and elastic modulus improved along with the increase of ZrO2 content and the optimal proportion was ASZ3. The result also verified the test result prepared by Nd:YAG laser. By experiment tests and theoretical calculation, the average microhardness of ASZ3 was about 2100HV and the average elastic modulus was 200 GPa, which were better than the current widespread clinical use ZTA mechanics performance. The effect of ZrO2 phase has changed in the sintering process and phase variable was 8.1%, which increased fracture toughness and improved the wear resistance.(6) ASZ1, ASZ2, ASZ3 phase transition during selective laser sintering process was analyzed by using the method of thermogravimetric and differential scanning calorimetry. In comparison of DSC-TG tests before and after laser sintering, there were no new substances before sintering and quality showed the tendency of decrease. After sintering mullite phase occurred, which can improve the service life and reliability. |
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