Study On Composition Design And Properties Of TiZr-Based Alloys For Biomedical Applications

The most widely used medical materials in clinical practice are metal biomaterials.Among of all metal biomaterials,titanium alloys have attracted more attention due to their non-toxicity,good biocompatibility,high specific strength,and low elastic modulus.In present,CP-Ti,Ti-6Al-4V and Ti-5A1-2.5Fe etc.have been widely used in biomedical field as the implant materials.However,their elastic modulus is higher than that of human bone,which will produce a"stress shielding effect"after implantation into the human body.Additionally,elements such as Al and V are toxic and will penetrate into the surrounding of the implant,causing human poisoning and even carcinogenicity and teratogenicity.Therefore,non-toxic,corrosion resistant and biocompatible biomedical titanium alloy has become a research hotspot.Based on this,the thesis aims at developing new biomedical materials,and a series of Ti-25Zr-xNb(x=0,5,10,15,20,25 wt.%)and Ti-20Zr-10Nb-xMo(x=0,3,6,9 wt.%)alloys compositions are designed by molybdenum equivalent method and d-electron alloy design theory in this paper.In order to explore the rolling deformation and heat treatment process parameters,the biomedical alloy system with low elastic modulus and good biocompatibility was designed,and the phase transformation,microstructure evolution and corrosion behavior of the alloy system were systematically studied.First,the effect of Nb additon on the microstructure,mechanical properties and corrosion resistance behavior of Ti-25Zr-xNb prepared via non-consumable vacuum arc melting furnace.The results show that with the increase of Nb content,the phase structure of the alloys change from???????+?????+???.The addition of Nb element improves the maximum compressive strength and compressive plasticity of Ti-25Zr-xNb alloys.When the Nb content is 25 wt.%,the compressive plasticity of the alloy is the best.When the Nb content is 15 wt.%,the self-corrosion current density i_corr value of the alloy in the 37?SBF is the minimum 94.3n A·cm^-2,and the maximum R_p value is 652.4 k?·cm~2,which indicates the best corrosion resistance.Secondly,Ti-25Zr-xNb alloy casted was hot rolled at 750?,and the rolling deformation was more than 80%.The microstructure and properties of hot-rolled Ti-25Zr-xNb alloys were studied.The results show that with the increase of Nb content in the alloys,the phase structure of the alloys change from?????+?????+???.The corrosion resistance of Ti-25Zr-xNb alloy in the 37?SBF is better than that of Ti-6Al-4V alloy.When the Nb content is 5 wt.%,the minimum self-corrosion current density i_corr value and the maximum R_p value of the alloy are 25.5 n A·cm^-2 and 2152.7 k?·cm~2,which indicate that the alloy has the best corrosion resistance.Thirdly,Ti-25Zr-15Nb alloy was heated into the single-phase region and the dual-phase region and hold for 1 h,and then cooled with the different rates,to study the effect of the cooling rate on the microstructure,mechanical properties and corrosion resistance behavior of the specimens.The results show that the Ti-25Zr-15Nb alloy after heat treatment is mainly composed of hexagonal?/??phase,orthorhombic???phase and body-centered cubic?phase.The phase region rises to the?unidirectional region,and the phase structure of the alloys undergoe a transformation of??+??????+???+?.After holding at 600?for 1 h and then cooling in the furnace,the maximum compressive strength,compressive yield strength,compressive plastic strain and maximum hardness of the alloy are 1300 MPa,780 MPa,27.3%and 307 HV0.2,respectively.The self-corrosion current density i_corr value of the alloy sample in the SBF at 37?is the minimum 22.2 n A·cm^-2,and the maximum R_p value is 2030.5 k?·cm~2.The alloy has the best corrosion resistance in this state.Finally,the effect of Mo content on the microstructure,mechanical properties and corrosion resistance of as-cast Ti-20Zr-10Nb-xMo alloys were studied.The results show that the phase structure of Ti-20Zr-10Nb-xMo alloys change from??+?????+???with the increase of Mo content;the average grain size increases with the increase of Mo content.increase and gradually decrease.After adding Mo element into the alloys,the maximum compressive strength and yield strength of the alloy show a trend of decreasing first and then increasing,while the microhardness first increases and then decreases.The self-corrosion current density i_corr value of Ti-20Zr-10Nb alloy in the SBF at 37?is the smallest 33.19n A·cm^-2,and the maximum polarization resistance R_p value is 1531.52 k?·cm~2,which has the best corrosion resistance.