| With the continuous development of laser selective melting(SLM)technology and the increasing demand for biological implant materials,the application of SLM has aroused wide attention of researchers at domestic and overseas in the field of medical implantation.The most important characteristics of SLM is that it can directly form parts of arbitrary shape and structure,It has shown great advantages in forming medical implants.TC4(Ti6Al4V)alloy has become an outstanding biomedical metal material because of its low density,high specific strength,excellent corrosion resistance and biocompatibility.However,because of the high melting point(1678?)and hardness,the traditional processing can not meet the processing requirements of TC4 alloy.The SLM technology is directly melting metal powder through high energy laser beam because its focusing temperature can reach more than 2000?.It is very suitable for the processing of TC4 the medical implant material.In the forming of artificial bones,joints and other different medical implants,it can give full play to the advantages of processing arbitrary shape and complex structure.Therefore,SLM is an effective and promising way to form medical implant materials.SLM to form TC4 biological implants requires the following characteristics.Firstly,the formed medical implant is required to meet the mechanical performance in the human environment;secondly,the implants generally need to have a certain wear resistance and corrosion resistance.Based on the above characteristics,mainly completed works are as follows.(1)The effect of laser power and scanning speed on the density,microstructure and mechanical properties by SLM were studied.The reasonable parameters were determined according to the microstructure and tensile fracture morphology.The experimental results show that the tensile strength,plasticity and fracture toughness of the prepared TC4 partsare best in the vicinity of the laser power of 300 W and the scanning speed of 1.5m/s.The tensile strength reaches 1227.13 MPa,the elongation reaches 8.2%,and the fracture morphology is characterized by toughness and para cleavage fracture.(2)In order to reduce the internal defects caused by high temperature gradient in the process of SLM,three heat treatment processes,ordinary annealing,recrystallization annealing and solid solution aging,were carry out on the formed samples.The results show that the annealing process of 800? recrystallization is the best to improve the performance of forming parts,the tensile strength is 862.96 MPa and the elongation is more than 10%,which is equal to the performance of the cast TC4.(3)The wear tests on the cast TC4 and TC4 formed by SLM samples were carried out.The wear morphology of the two parts was observed by SEM scanning electron microscope,and the influence of SLM process on the wear resistance of TC4 material was analyzed.The results show that the wear resistance of cast TC4 is not as good as the deposited samples.The wear mechanism of the two samples is abrasive wear and adhesive wear coexisting.The difference is that the hardness of the deposited TC4 is higher,and the wear process is more stable.(4)Electrochemical corrosion test of TC4 specimen by SLM in Hank 's human biomimetic solution.The effect of different heat treatment processes on corrosion resistance of TC4 by SLM is studied.The results show that the corrosion resistance of the deposited TC4 is not as good as cast TC4,and the corrosion rate of cast TC4 is slow,and the passivation range is wide,and the corrosion resistance is better.On the other hand,annealing treatment can improve the corrosion resistance of TC4 specimens formed by SLM.The reason is that heat treatment promotes the transformation of anatase to rutile,while rutile six side crystal system has more stable structure and stronger chemical resistance. |
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