Research On Metal Injection Molding Of Biomedical Titanium Alloys

Titanium and titanium alloys are the most promising biomedical materials due to their high specific strength,low elastic modulus,excellent corrosion resistance and bio-compatibility.Compared with other processing methods,powder injection molding can achieve mass production of biomedical titanium alloy components of complex shape and structure with higher material utilization ratio.However,the commonly used wax-based feedstock can not meet the production requirements of micro titanium alloy biomedical components.In this paper water-soluble titanium alloy feedstock with good formability and high removal of binder was developed.After that,the production process of high performance biomedical titanium alloy small / micro component injection molding was studied.The characteristics of binder system being thermodynamically incompatible and process compatible were determined by thermodynamic calculation and micro-morphology analysis,which provided a theoretical basis for binder removal by two-step debinding process.According to the viscosity,strength and rheological properties of the feedstock and the microcosmic morphology analysis,the best binder component of PEG:PMMA:SA=86:12:2 was determined.The best powder loading quantity of 66% of the feedstock was determined with the characteristic analysis of feedstock with different powder loading.The debinding mechanism and debinding process were studied.The mathematical model of PEG component dissolution and removal was established by using Fick's diffusion law,and the relationship between PEG component removal rate and debinding time was determined.Based on the oxygen and carbon content of the thermal debinding samples,the influence of the process parameters on the debinding efficiency was studied,and the optimum process parameters were determined to realize the low residual removal of the binder in the samples.The effects of sintering process parameters on the relative density and chemical composition of sintered parts were studied experimentally.Increasing the sintering temperature,decreasing the heating rate and prolonging the holding time can increase the relative density of the sintered part,but increasing the impurity content and grain size of the sintered part at the same time.Vacuum sintering,metal sintering substrate and oxygen absorbent can reduce the impurity content in the sample.Based on the optimized process parameters of debinding and sintering,the titanium alloy products with proper relative density,mechanical properties and impurity content can meet the standard of ASTM for surgical implants,and the shape preservation of the sintered products is good as well.The sintering process of titanium alloy injection molding was simulated using an elasticthermal-viscoplastic model.The model parameters were calibrated and coupled with Matlab software through bending beam sintering experiment.Then the sintering process was simulated using Abaqus software.The simulation results were in good agreement with the experimental results.Finally,the artificial ossicular prosthesis conforming to the standard of ASTM F2989-13 was successfully prepared by using the fine powder pure titanium feedstock.The results of acoustic performance test showed that the temporal bone structure of the prosthesis was consistent with that of the normal middle ear chain.The feasibility of produce titanium alloy small/micro components for surgical implantation by injection molding is proved by the example.