| ? titanium alloy has become a new generation of biomedical metal materials due to its lower Young's modulus,better biomechanical properties,biocompatibility and corrosion resistance.Ti-15Mo alloy was prepared by vacuum consumable arc melting.The aging precipitation behavior and deformation aging mechanism of Ti-15Mo alloy were studied by optical microscope(OM),X-ray diffraction(XRD),electron backscatter diffraction(EBSD),transmission electron microscopy(TEM)and highresolution transmission electron microscopy(HRTEM).Combined with the microstructure evolution,the tensile properties,springback properties and corrosion resistance mechanism of the alloy were tested and analyzed.The main conclusions are as follows:(1)After solution treatment at 800? for 1h,the alloy consists of supercooled ?phase and a small amount of athermal ? phase(?ath).At the beginning of aging,the ?athphase clusters and grows to the isothermal ? phase(?iso);The supercooled ? phase was decomposed in the form of ???rich+?poor??rich+???+?.During the decomposition,ellipsoidal ?iso phase was precipitated.With the extension of aging time,?iso phase grew up and transformed to ? phase.The nucleation and growth of ? phase are controlled by long-range diffusion of solute atoms and the growth rate is controlled by diffusion rate.(2)The nucleation of ? phase occurs preferentially at the ?/? interface.There is a concentration gradient difference between ? phase and ? phase,which causes the diffusion of solute atoms,leading to the indirect influence of ? phase on the precipitation of ? phase through the composition gap with low Mo content.Due to the adaptive regulation of ? variants,(0001)?1,2,3 and(0110)?1,2,3 variants were observed in the samples aged at 450? for 180h.The orientation relationship between ? variant and? matrix is:<111>?//<2110>?,{110}?//{0001}?.(3)Isoaxial ? phase microstructure was obtained after solution treatment at 800?for 1h,the ultimate tensile strength was 725MPa and the elongation was 44%.When the alloy aged below 450?,the precipitation of ? phase causes a significant increase in strength and a sharp decrease in plasticity.When the alloy is aged at 550?,the strength increases first and then decreases with the extension of aging time,the Young's modulus increases,and the elongation decreases.Excessive aging time will lead to stress concentration and crack initiation due to grain boundary coarsening.The alloy aged at 550? for 1h has the best comprehensive mechanical properties.(4)The microstructure evolution as well its effect on the mechanical properties of Ti-15Mo alloys after solution treatment(ST),cold rolling(CR),aging(STA)and aging after cold rolling(CRA)were investigated.The Young's modulus of the alloys after ST,CR,STA and CRA are all less than 60GPa.Compared with the ST sample,the plasticity of the alloy after CR,STA and CRA treatment is within the scope of application(>10%),and the strength is significantly improved,which is attributed to the strengthening effect of twins,dislocations,deformation-induced ? phase and isothermal ? phase.The springback of Ti-15Mo alloy is lower than that of new metastable Ti-30Zr-3Cr-3Mo and Ti-29Nb-13Ta-4.6Zr alloys.Therefore,from the Young's modulus,tensile and springback properties,Ti-15Mo alloy is more easily used as a spinal fixation device in clinical applications.(5)Ti-15Mo alloy exhibits lower corrosion tendency than Ti-6AI-4V ELI alloy in Ringer's simulated body fluid.Due to the influence of the second phase particles,the corrosion tendency of the alloy increases with the increase of aging temperature and aging time.After deformation and aging,stress induces ? phase transformation and isothermal ? phase precipitation,which hinders dislocation slip.The formation of highdensity dislocation provides a channel for local corrosion of the alloy and increases the corrosion tendency. |
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