Direct Inject Printing Of SiOC Ceramics And Mechanical Properties

Ceramic materials have many advantages such as high strength,high hardness and excellent high temperature stability,and are considered as the first choice for the materials of aero engines.However,its high hardness results in the traditional（Computerized Numerical Control Machine）molding process can only shape simple components with low precision molding but high cost.Thus there is a big limitation in the formation of complex structural ceramic components,making its application restricted.Therefore,in this paper,SiO₂-HPSO/DVB ceramic precursors were used as the raw material system,and several kinds of structural ceramic precursors were prepared by DIP molding.Dense SiO_C ceramic components were prepared by pressureless pyrolysis reaction.The effect of DIP molding process and pyrolysis temperature on the size shrinkage behavior,microstructure and mechanical properties of SiO_C ceramics was studied.The results showed that the the system with SiO₂ solids content of 19.35% had a viscosity of 1448.88（Pa·s）at a shear rate of r=0.13（1/s）,and there was a yield point for solid and liquid state.Thus it was suitable as a DIP molding material system.The SiO_C ceramic components prepared by DIP molding were well connected at the interface where the ink was connected parallelly and vertically.The analysis of the linear shrinkage rate for the pyrolysis showed that the linear shrinkage rate in the Z direction was only related to the pyrolysis temperature and the thickness of the slice.As the pyrolysis temperature or the thickness of the slice increased,the linear shrinkage rate in the Z direction increased.In addition,through actual measurement and theoretical analysis,it was proved that the linear shrinkage of the plane is related to the pore structure but not the pore size of the model.The cross-linking process of the 19.35%SiO₂-HPSO/DVB ceramic precursor produced a hydrosilylation reaction between Si-H and C=C to form a three-dimensional network macromolecular structure.When the pyrolysis temperature reached 800°C,the system became an inorganic phase and as the temperature increased,the content of Xhigh-value of [SiO₄-XCX] structure increased,and the macroscopic appearance was that the SiO_C ceramic system gradually changed from amorphous to β-Si C phase.In the process of component transformation with temperature,graphite C underwent carbothermal reduction reaction with SiO₂ at high temperature.In addition,the presence of graphite C prevented the short-range diffusion of crystal grains and inhibited the crystallization of β-Si C and t-SiO₂.Due to the lubricating effect of graphite on the surface of ceramic particles,the reduction of the size of ceramic particles and the growth of fibrous substances,the hardness,compressive strength,and bending strength of the SiO_C ceramics prepared by DIP molding reduced with the increasement of the pyrolysis temperature.As the slice thickness of the slice increased,the width of the bearing surface decreased,and the mechanical stability of the ceramic decreased.When the ratio of Vprint/Vinject is large,the ink could not be uniformly elongated and the intermittent thinning behavior occured.The tapering became a structural defect,and the stress concentration occured during the stress and the destruction,in turn,reduced the mechanical properties of SiO_C ceramics.The measured flexural performance of the 80% filled parts was not significantly different from the 100% fullness,but as the filling level was further reduced,the insufficient internal support material resulted in a decrease in flexural performance.In addition,non-100% filled ceramic components could fill part of air inside,which easily reacted with the ceramic itself and cause changes in ceramic composition and microstructure in the high temperature conditions,this change directly affected the mechanical properties of the ceramics.