Injection Molding Research Of Silicon Nitride Materials

As a net size forming method,ceramic injection molding process has the advantages of short molding cycle,uniform green density and excellent performance of sintered products,especially for the preparation of ceramic products with small size,complex shape and high dimensional accuracy.In this thesis,industrial grade silicon nitride powder was selected as raw material.The effects of different binders on injection molding feed and the change of non-Newtonian index of feed at 140～160℃ were studied.The binder system and feed preparation process were determined.The influence of injection molding parameters on the green body was analyzed.The thermal decomposition curves of the main components of the binder system and the green body were measured,and a suitable thermal degreasing curve was developed.The sintering kinetics test and microstructure analysis were carried out.The main results are as follows:（1）The binder system of EVA and LDPE has good fluidity and uniform dispersion in the process of slurry preparation.（2）By changing the influence of the composition of the binder system on the feeding and forming body,it is concluded that when the ratio of paraffin to macromolecular binder is 0.9,the strength of the green body is higher,and the optimum powder solid content of the feeding under this system is 52.42 vol.%.（3）The feedstock with a loading of 52.42 vol.%is a non-Newtonian pseudoplastic fluid at 140～160℃,and the rheological properties are the best at 160℃.When the shear rate is 200.00 s^-1,the viscous flow activation energy is 12.57 KJ/mol,indicating that the change of temperature has little effect on the feed.（4）In the ceramic injection molding process,the injection temperature,injection pressure,mold temperature,packing pressure and cooling time and other parameters have an impact on the products.The products are prone to under-injection,flash,deformation,holes,fracture and other defects.The recommended process parameters of ceramic injection molding are as follows:injection temperature 165℃,injection pressure 85 MPa,holding pressure 75 MPa,cooling time 5 s,mold temperature 45℃.（5）The thermal decomposition curves of the main components of the binder system were analyzed,the thermal decomposition range of each component was determined,and the thermal weight loss curve of the green body was integrated to develop a suitable thermal degreasing heating system.（6）The sintering kinetics of the degreased samples was tested by a multi-function furnace（TOM-AC）.The results show that the key control temperature point of silicon nitride ceramics is 1400℃.The sintering temperature was 1790℃ and the atmosphere pressure was 4 MPa.The density of the prepared ceramic products is 3.23 g/cm³,the Vickers hardness is 15.24 GPa,the fracture toughness is 5.98 MPa·m^1/2,and the shrinkage of the body is about 19.9%.