Study On Process And Properties Of Medical Porous Ti6Al4V(ELI)Alloy Formed By SLM

Bone defect is a common orthopaedic disease and surgical repair is often needed for large bone defect.However,the use of natural bone substitutes such as autogenous bone and allogeneic bone cannot meets the needs of personalized repair.Therefore,there is an urgent need for customized orthopaedic implants according to different repair needs.Selective Laser Melting(SLM)technology,the most promising aspect of Additive Manufacturing technology,is featured by high precision and density of shaping,and can produce parts with complex structure.Ti6Al4V(ELI)alloy is widely used in medical implants due to its high strength,good corrosion resistance,good biocompatibility,as well as low elastic modulus.And the introduction of porous structure into the implant can eliminate mismatch between the mechanical properties of traditional dense implants and human bones.Based on different demand for bone repair,the processing parameters were discussed from single tracks to dense bulk and then porous structure using SLM technology;octahedral and dodecahedron structure with different porosity/relative density and strut thickness were designed and precisely fabricated;the effect of porosity/relative density and strut thickness on mechanical response and properties were analyzed;and the effect of different heat treatment on compressive deformation behavior and mechanical properties of porous Ti6Al4V(ELI)alloy were studied.The main contents and results are as follows:(1)The process parameters of Ti6Al4V(ELI)alloy were optimized.The relationship between track width and energy density were developed based on the single-track experiments;The Ti6Al4V(ELI)alloy with different densities was formed by adjusting the hatch distance using the smooth and continuous track,and density,surface roughness,tensile properties and corrosion resistance were analyzed.The results show that the width of track grew up with the increase of energy density.And with the increase of hatch distance,the density,tensile strength and side surface roughness of bulk material first stabilized and then gradually decreased;the roughness of upper surface,electrochemical corrosion potential and current density continued to decrease.(2)The influence factors of mechanical properties of porous Ti6Al4V(ELI)alloy formed by SLM were studied.According to the requirements of biomechanical properties,the porous structures of octahedron and dodecahedron structure were designed and precisely manufactured.Porosity,strut thickness,compressive properties and dynamic elastic modulus of formed porous Ti6Al4V(ELI)alloy were measured.Results show that,SLM technique can fabricated the designed high-porosity porous Ti6Al4V(ELI)alloy accurately and the error between the actual porosity and the designed one is within 0.3%.The compressive strain response of regular octahedral porous Ti6Al4V(ELI)alloy conforms to the characteristics of porous materials.The compressive strength and energy absorption of porous Ti6Al4V(ELI)alloy increases with the increase of relative density,and the relationship with relative density is exponential.Compared with dodecahedral structure,porous Ti6Al4V(ELI)alloy with octahedral structure has higher compressive strength and strain behavior are more stable,which is more suitable for implant structure.The dynamic elastic modulus of porous Ti6Al4V(ELI)alloy also increases with the increase of relative density,which conforms to Gibson-Ashby model.(3)The effect of heat treatment on the properties of SLM-ed octahedral porous Ti6Al4V(ELI)alloy was studied.And heat treatment was carried out near the phase transition temperature of titanium alloy.The results showed that the compressive stress-strain curves of porous Ti6Al4V(ELI)alloy after heat treatment was smoother and more suitable for the energy absorption of the implant.The phase composition of Ti6Al4V(ELI)alloy did not change obviously before and after heat treatment,but the microstructure of Ti6Al4V(ELI)alloy grew gradually with the increase of heat treatment temperature.The effect of different heat treatment on dynamic elastic modulus of porous Ti6Al4V(ELI)alloy is not obvious.There was enough time for the diffusion of alloying elements in the heat treatment process,and obvious element segregation occurred in the Ti6Al4V(ELI)alloy after heat treatment.