The Investigation Of Microstructure And Properties Of Titanium Alloys With Low Elastic Modulus For Biomedical Applications

Titanium alloys for biomedical applications have been widely used as hard tissue repairing and replacing materials,such as human body skeletons and teeth,due to its excellent combination of mechanical properties and corrosion resistance.However,there are many shortages in titanium alloys used in clinical applications,high elastic modulus,and toxicity of alloying elements such as Al and V etc.In the article,to get low elastic modulus titanium alloy biomaterials,selecting Nb and Zr as additional elements for their good biocompatibility, the compositons of Ti-Nb-Zr alloys are designed by means of cluster line criterion method and component matching method respectively.Studies on phase constitutions and microstructure under different processing technologies and heat treatment conditions are completed by optical microscope(OM),scanning electron microscope(SEM)and X-ray diffraction(XRD);elastic modulus of the alloys are measured by supersonic method and tensile method respectively,and effects of different chemical compositions and heat treatments on elastic modulus are studied mainly,and basic mechanical properties are also investigated.The X-ray diffraction analyses of Ti_14-xNb₁Zr_x(at.)series skull casting and suction-casting alloys designed by cluster line criterion method revealβ+α' microstucture,the dynamic elastic modulus are from 71 to 76GPa,and increase with increasing content of Zr. The method of suction-casting fails to retain the bcc structure with Nb as centeral atom in liquid alloys from high temperatue to room temperature,not getting the alloys with onlyβphase.Ti-xNb-7Zr(wt.%)series alloys designed by component matching method made up ofβ, acicularα" and tenticularα' phases after solution treatment lead to low dynamic elastic modulus,which are the 60～70%of the modulus of Ti-6Al-4V alloy(about 110GPa). Ti-18Nb-7Zr alloy has the lowest modulus,about 67.2GPa.The microstucture of Ti-18Nb-7Zr alloy after aging treatment consists ofβ+αphases,and shows lamellar pattern aged at 350～450℃,growing up with the increase of aging temperature;shows needle pattern aged at 500℃.The elastic modulus and compressive strength increase with increased aging temperature.Ti-27Nb-8Zr(wt.%)alloy subjected to solution treatment at 800℃after hot rolling is comprised ofβand acicularα" phases,and has occurred recrystallization with average grain size about 55μm.The alloy has lower elastic modulus(72GPa),tensile strength and better plasticity.The yield strength is 348MPa,tensile strength is 505MPa,elongation is 58%and reduction of area is 69%.The metastableα" andβphases have decomposed after aging treatment,the microstmcture of the alloys are comprised of free dispersed precipitatedωandβphase aged at 350～400℃,and comprised of granularω,a few thin-needleαandβphases aged at 450℃.When aging temperature is 500℃,the microstructure of the alloy is made up of free dispersed distributed thin-needleαandβphases.While the micostucture of the alloys include the hard and brittleωprecipitation phase,the elastic modulus and tensile strength of the alloys are higher,but the plasticity is lower,a better combined mechanical properties could be obtained aged at 500℃.Meanwhile,the alloy possesses preferable fatigue resistance under 500℃aging temperature,its fatigue limitσ_max≥400MPa,as high as twice than fatigue limit of commercially pure titanium.