Study On The Properties Of Human Implants With Irregular Porous Structure Based On SLM Titanium Alloy

Human bone is a heterogeneous composite material with an irregular pore structure inside;even in the same part,the mechanical properties are very different in all directions,which is caused by the mismatch between the elastic modulus of the implanted substitute and the original bone"Stress shielding".Although,in response to this problem,some studies have proposed that the use of selective laser melting SLM to prepare titanium alloy irregular porous structure human implants is a very effective method,which can reduce the Young's modulus of the solid structure implant to that of human bone tissue.Within the range of modulus,it can reduce the difference in mechanical properties between bone tissue and titanium implants,and solve the"stress shielding"problem to a certain extent;however,SLM prepares a porous structure,and residues will accumulate inside the sample during the molding process.Stress leads to poor plasticity of the sample,poor fatigue performance,and brittle fracture.Therefore,in this thesis,titanium alloy material Ti6Al4V is selected,based on orthogonal analysis with density as the goal,the SLM molding process parameters are optimized,and the human body implant with irregular porous structure is prepared.At the same time,according to the material characteristics,the annealing heat treatment process is used to eliminate the sample The residual stress generated during the molding process improves the mechanical properties and fatigue properties of the sample.The specific research content of this article is as follows:Firstly,based on the Voronoi-tessellation principle,the Grasshopper plug-in is used for parametric design to realize the modeling of irregular porous structures.Through orthogonal test analysis,with the goal of optimizing the density,the best molding process parameters are determined.Secondly,according to the characteristics of SLM samples,two groups of annealing processes are selected to eliminate stress annealing and complete annealing.The effect of two annealing processes on microstructure and microhardness is different.Stress Relief annealing mainly eliminates the residual stress of porous structure in the process of forming SLM,and the change of microstructure is not obvious The microstructure was changed by complete annealing heat treatment while the residual stress was eliminated,and the microstructure was transformed from the metastable?'phase to the stable?+?phase.Thirdly,the quasi-static compressive mechanical properties of the porous structure designed in this thesis are tested.The young's Modulus of porous structure in the range of0.1-30GPA can meet the requirement of the mechanical properties of bone and improve the compressive strength.At the same time,it is verified that the young's Modulus and compressive strength of irregular porous structure decrease with the increase of porosity,which is consistent with Gibson-Ashby model.Finally,the fatigue mechanical performance test,fatigue test at 0.2?_y stress level.The fatigue properties of the porous structure were compared before and after annealing.It was found that the fatigue properties of the porous structure increased with the decrease of porosity.At the same time,annealing heat treatment greatly improves the fatigue property of the porous structure.The number of cycles of the porous structure after complete annealing is more than 4 times that of the unannealed porous structure.