Research On Microstucture And Mechanical Properties Of Biomedical Near ?-type TLM Titanium Alloy Thin Strip

The near P-type Ti-3Zr-2Sn-3Mo-25Nb(TLM) titanium alloy has low elastic modulus and good biocompatibility, which make it has a good prospect in dental implant, joint replacement, intravascular stents and other biomedical application. Its thin strip can be processed into various medical equipments, such as active implantable medical device's casing, operation equipments and so on.The phase transformation and microstructure changes of near ?-titanium alloy in the process of plastic deformation and heat treatment enable its performance to vary in a wide range. This article makes a research on the different states before and after plastic deformation and heat treatment process of the titanium alloy by cold rolling and heat treatment of its thin strip. The micro structrue, phase composition, mechanical properties and forming performance of the alloys are analyzed and researched by means of OM, TEM, XRD analysis and tensile test, bending test, cupping test. The main conclusions are as follow:The original annealed TLM alloy thin strip is mainly composed of a single ? phase. The strength, hardness of the alloy increase significantly, and the ductility decreases after 67% cold rolling deformation. At the same time, after a large amount of plastic deformation, a fine grain structure can be obtained. In the process of cold rolling deformation, deformation martensitic phase transformation happens which generates the martensite phase a".The deformation martensite phase a" disappears after solution treatment of the cold-rolled alloy and the new quenched martensite phase a" forms. With the increase of the solution temperature, the grain size of the alloy increases. The strength and hardness of the alloy decrease and the ductility increases.750? achieves a better match of strength and ductility.The mechanical properties of TLM alloy can be regulated by aging treatment. The TLM alloy solution treated at 750? generates highly dispersed ?-phase after with 350? and 400? aging treatments. The strength, hardness of the alloy increase, while the ductility decreases; After with 450? and 510? aging treatments, the ?-phase gradually disappears, and a huge amount of a-phase generates which leads decrease of the strength and hardness and a increase of the ductility.By observance of micro structure of the fracture on the specimen after tensile test, the characters of the deformation martensite's phase transformation in different states are analyzed as:A large number of lath deformation martensite appears in 750? solutioned tensile specimens; The deformation martensite is less in the tensile specimens when aging at low temperature; while it takes more contents when aging at high temperature than that when at low, but it is still less than when in the solution state.Bending and Cupping test results show that:The bending and forming abilities of TLM alloy thin strip is a bit worse after cold rolling; The bending and forming abilities of TLM alloy thin strip is excellent after solution treatment; Aging treatment reduces the bending angle and cupping value of the alloy thin strip and has a great effect on the formability of the alloy, the formability parameters increase with the rise of aging temperature.