| Injection molding of ceramics (CIM) is considered as a promising shaping technique. An investigation was started to test whether injection molding of yttrium oxide stabilized tetragonal zirconia can result in products with good mechanical properties. The results have shown as the following:An oil-wax-based binder system with 50vol% zirconia was injection-molded. The binder system can meet the demand of the zirconia powder (the average size of 0.8lμm ) selected in the experiment. The binder has good wetting qualities with the powder and the feedstock has favorable rheological behavior. The binder can be removed by the step-by-step debinding.For the samples injected, the molding temperature and molding pressure are the key process parameters of the molding process of feedstock. The optimal molding parameters for the feedstock are as following: temperature for molding 155 ±5 ℃, molding pressure 60-70%. Other parameters are as following: temperature of mould 55±5℃, holding pressure about 55%.The next step, solvent debinding was done in water bath equipment. The particle shape and its size, character of solvent, shape of the green parts and temperature has strong influence to the solvent debinding results. The thermal decomposition behaviors of binders and feedstock are also studied to find process conditions during which the binder can be completely removed from the products without damage or dimensional change. After investigating carefully, the best debinding process of different samples have been obtained respectively.After that, by series of experiments, the author of the dissertation has got the optimal sintering process. The sintering of the green products was done in a superkanthal furnace with air atmosphere. A temperature-time profile was determined in which full densification occurred, but no excessive grain growth took place.The main limitation of CIM is the control of defects, however, these can arise in any of the processing stages. The causes of the defects in injection-moulded ceramic samples during injecting, debinding and sintering process were investigated. The mostAbstractsignificant defects that occur during injection molding are voids and cracks, modulated molding pressure and temperature have been used to diminish voids formation. The causes of defects during debinding and sintering are far more complicated and difficult to isolate. However, it has been observed that the defects, which develop during debinding and sintering, may originate from the injection stage. The mechanical properties and other properties of the sintered parts produced compare favorably to those of commercially available zirconia materials. It appears very dependent on the shape and size of the samples. Comparing with the traditional method of P/M of manufacturing ceramics, the advantage of CIM is the fabrication of complex shapes for small section components and the problems of preparing large components continue to be explored. Finally, the effects of defects on the strength of samples were investigated. The strength diagram of materials with crack was calculated and was also compared with experimental results. |
