Study On Injection Molding Of Sialon Ceramics

Silion Nitride(Si₃N₄)is one of the structural ceramics with excellent properties applied at high temperature.Si and N in Si₃N₄ structure can be replaced by Al and O to form a new ceramic called Sialon,which has the same crystal structure as Si₃N₄ and also keeps the perfect properties.Consequently,Sialon has been applied to fabricating small parts of engine as an optimum material.However,the molding method is the key problem which blocks the development because of the complex shaped parts of the engine.Ceramic Injection Molding is a near-net-shape forming process for fabricating ceramic components,which is a promising method for fabricating samples with high precision and complex shape.It receives great attention now.In this paper,the injection molding process of Sialon ceramic injection molding was studied.The preparation of the powder and the binders,and the rheology of feedstock were investigated,as well as the binder removal and sintered technology etc.,in order to find out the key factor and obtain defect-free ceramic samples in the end.In this paper,two kinds of Si₃N₄ powders were used for the preparation of Sialon powders.Sialon powder was mixed with the wax-based binder systems.And feedstocks of different powder loadings were prepared.The capillary rheometer was used to obtain the viscosity of feedstock at different temperatures and share rates,and test the rheology. Then feedstock showing best rhelogy was chosen to be the final feedstock.Molding process is one of the key steps.Based on the researching experience on self-design injection molding equipment,molding process was accomplished using CJ80-E Plastic injection machine.The effects of different injection parameters on the quality of molded bodies were studied.Then suitable injection parameters were determined.Meanwhile,the causes of the defects in molded bodies during injecting were investigated and analyzed.The methods for optimizing the parameters to avoid the defects were developed.The binder was removed through thermal debinding process.Thermal degradation behavior of organic binders was studied,and the melting point and degradation temperature were determined.Combined with thermogravimetry of feedstock and the characteristic of parts,the reasonable heating system of binder removal was determined. The defect-free samples were successfully obtained. The pressless sintering and ageing process had been studied.The density and shrinkage rate of the samples were measured after heat treatment.The mechanical properties were also tested.The results showed that the samples fabricated by injection molding have the similar properties as those by mould pressing.