Effect Of Topology On The Mechanical Properties And Permeability Of 3D Printed Porous Titanium Alloy

The orthopedic implants with a porous structure can effectively avoid the stress shielding,facilitate bone ingrowth,and improve the success rate of implantation.However,the bone tissues have different mechanical properties and permeability in human body,so the requirements of porous implants are also different.It is necessary to further study the differences in mechanical properties and permeability of different porous implants to provide the theoretical basis for designing new porous bone implants.In this thesis,different porous titanium alloys?Ti6Al4V?were manufactured by selective laser melting?SLM?,and the heat treatment process of as-built samples was studied.The mechanical properties and permeability of porous samples with variable porosity were researched.The finite element analysis?FE?was used to study the deformation behavior and permeability of the porous structures.The conclusions of the full text are as follows:?1?In this thesis,three kinds of porous structures Primitive,Gyroid and BCC with a porosity of 65%were designed,heat-treated at 850?and 950?,and the mechanical properties of porous Ti6Al4V samples were tested.The results showed that heat treatment made the microstructure of porous samples more uniform,and transformed the needle-like?'phase in as-built samples into?lath and?+?microstructure,improved the plasticity of porous samples.When the as-built samples heat-treated at 950?for 2 hours and following by furnace cooling,the samples had excellent microstructural and mechanical stability.The porous samples with different topologies had different mechanical properties at the same porosity.Among them,BCC samples had the lowest compressive and tensile strengths of 216.0±5.1MPa and143.0±1.3MPa,respectively,and Gyroid samples the highest compressive and tensile strength of 321.3±17.2MPa and 321.3±17.2MPa respectively,while the compressive and tensile strength of Primitive was 295.4±1.8MPa and 261.2±16.2MPa respectively.It can be seen that the strength of porous samples differed by nearly 180MPa even though they had the same porosity?65%?,and the pore cell topology had a huge influence on the strength of porous materials except the porosity of samples.It can be seen that in addition to the parameter of porosity,the topology of the pore unit has a huge influence on the strength of the porous samples.?2?Four porous structures were designed and fabricated in this work,which were Primitive,Gyroid,Diamond,and IW-P,respectively.And each of them had four different porosities,55%,65%,75%,and 85%.The as-built samples were heat-treated at 950?for 2 hours,and then the mechanical properties of the samples were tested.At the same time,the compressive deformation behaviors of four porous structures were simulated by FE.The results showed that the compressive strength of Primitive was not as good as the other three porous samples,and the compressive strength of IW-P was the best,but IW-P was prone to fracture in compression.The Gyroid structure had better stress conductivity,and its compressive stress-strain curve was smoother.In the relationship between the relative density of porous samples and the relative mechanical strength and relative elastic modulus,the experimental values were well fitted with the predicted curves.It was found that the interior of the porous structure unit yielded and bended firstly when simulated the compressive deformation behaviors of porous structures by FE.?3?The permeability simulation of the above four porous structures was conducted by FE in this work.The results indicated that the permeability of the porous structure was mainly related to its topological morphology at the same porosity.The simpler the topological morphology of the porous structure,the larger the pore size,the greater the permeability coefficient of porous structures would have.And the Primitive structure had the largest permeability,and its maximum permeability was 10.6×10^-9 m².