Development Of Injection Molding Process Of 3YSZ Powder With High Specific Surface Area And Study On Mechanical Properties Of The Products

With the application of advanced ceramic materials in mechanical structural parts,intelligent wearable device,aerospace,and other fields closely related to people’s production and life,people put forward higher requirements for the complexity of the shape of ceramic products.Among many ceramic material molding processes,ceramic powder injection molding（CIM）is a common process for continuous preparation of advanced ceramic products with complex shapes.However,in order to reduce powder agglomeration,control feedstock uniformity and reduce molding and debinding defects,the specific surface area of raw material powder used in CIM process is usually less than 12 m²/g,which not only limits the selection range of raw material powder,but also abandons the advantages of high specific surface area,such as high sintering activity and good product performance.Therefore,improving the specific surface area of raw material powder in CIM process and successfully obtaining products with excellent mechanical properties will provide an effective supplement to the current CIM industry.Based on this,this thesis selects 3YSZ as raw material,develops a set of injection molding process suitable for 3YSZ powder with high specific surface area（18 m²/g）and obtain products with excellent mechanical properties.Taking the process flow of CIM process as the main line,it is carried out in sequence:optimize the feedstock preparation and molding process,the feedstock with uniform mixing of binder and powder is obtained,and the green body with high dimensional accuracy is successfully injected;By optimizing the debinding and sintering process,the degreased body with complete binder removal and no deformation and cracking was obtained,and the sintered compact products were obtained at different temperatures;Test the mechanical properties of different products,and explore the effect of grain size on the mechanical properties of products and its mechanism.The main research contents are as follows:（1）The binder system of 50%paraffin+30%high density polyethylene+12%microcrystalline paraffin+5%polymethacrylic acid+1.5%dioctyl phthalate+1.5%stearic acid was selected.By observing the torque change of feedstocks with different solid loding,it is determined that the optimal solid loding is 85 wt.%.Combined with the TG-DSC curve of the binder system,after internal mixing at 195℃and granulation at 130℃,The feedstock with uniform powder dispersion and good fluidity under heating conditions was obtained.Combined with the actual production environment and orthogonal test method,the appropriate injection parameters were determined.Holding the temperature of the fixed mold at 30℃and the cooling time at 12 s,the best injection parameters are:the injection temperature is 165℃,the injection pressure is 110 kg,the injection speed is 85%,and the holding pressure is 70 kg for 1 s.Under these injection parameters,the green body with complete mold filling,smooth surface and no crack was obtained.（2）Using the two-step debinding process of solvent debinding and thermal debinding,the degreased body with no binder and no new defects was obtained and sintered at different temperatures.When kerosene is used as debinding solvent,the soluble components with low melting point can be completely removed by soaking in 50℃for 4h.Combined with the TG-DSC curve of solvent degreased body,the thermal debinding process was optimized.The degreased body has no obvious shape change.No obvious defects were found through its microstructure.Due to the high sintering activity brought by high specific surface area powder,sintered products with relative density of more than 98%can be obtained by holding at 1350℃～1550℃for 3 hours;（3）The phase composition of the samples obtained at different sintering temperatures was analyzed,their mechanical properties were tested,and their surfaces’and sections’microstructure were characterized.The main crystalline phase of all samples is tetragonal phase.When the sintering temperature is 1350℃,the Vickers hardness of the samples is the highest,which is 13.42 GPa;When the sintering temperature is 1550℃,the fracture toughness of the sample is the highest,which is 7.85 MPa·m^1/2.With the increase of sintering temperature,the Vickers hardness of the sample gradually decreases and the fracture toughness gradually increases.Through the microstructure,fracture mode and phase change at the indentation of the sample,it is determined that for the ceramic sample prepared by this3YSZ powder,the Vickers hardness is mainly controlled by the fine grain strengthening mechanism and the fracture toughness is mainly controlled by the phase transformation toughening mechanism.When the sintering temperature reaches 1550℃,there will be a certain amount of microcrack toughening.In summary,through the research of this thesis,based on the selection of a suitable binder system,the difficulty that high specific surface area ceramic powder is not easy to be formed and degreased was overcome,and a set of injection molding process applicable to3YSZ powder with specific surface area of 18 m²/g was successfully developed and optimized.Meanwhile,the sintering temperature is reduced,and the dense 3YSZ ceramic products with excellent mechanical properties can be obtained by sintering at 1350℃.The mechanical properties of the samples can be controlled directionally by adjusting the sintering temperature,which can meet the needs of applications in different situations.The results of this thesis provide a certain complement to the current CIM industry.