| Titanium and titanium alloy has excellent corrosion resistance and biocompatibility. Due to theincreasing concern over the allergic and carcinogenic effects of Ni element on the human body,the βtitanium alloys composed of non-toxic and non-allergic elements, are highly attractive for biomedical devices.Among all the Ptitanium alloy systems, Ti-Nb-Zr alloy system has many distinctive properties such as low Young's modulus, relatively higher strength, superelasticity and shape memory effect. Therefore, Ti-Nb-Zr system alloy is considered to be a good candidate for hard tissue replacement materials and biomedical superelastic alloys.Almost all the published research work about the Ti-Nb-Zr system alloy is based on the result of laboratory scale button ingot with very low interstitial elements content. However, the titanium ingot for largescale application is produced by VAR melting process, which could introduce relativelyhigher interstitial elements content into the ingot. Interstitial elements have significiant effect on the phase transformation, mechanical property and workability of the Ti-Nb-Zr system alloy. In this paper, the microstructure, phase transformation and mechanical property of the Ti-Nb-Zr system alloys for hard tissue replacement and superelasticity application,respectively, are studied based on the VAR prepared ingots.For the purpose of getting low Young's modulus, the Ti-26Nb-4Zr(at.%) alloy design for hard tissue replacement application is resorted by Bo-Md map based on the DV Xa theory.Tested Young's modulus of the Ti-26Nb-4Zr alloyin solution condition, which is not larger than60GPa, is in good agreement with predicted value given by Bo-Md map. Aging response of the Ti-26Nb-4Zr alloy is sluggish because of the very high Nb content in this alloy. Tensile strength of the Ti-26Nb-4Zr alloy in STA condition is up to700MPa, while the Young's modulus is about70GPa. Ti-26Nb-4Zr alloy has excellent cold workability, the maxium cold rolling reduction without intermediate annealing is up to93%. Interstitial elements introduced by VAR melting process have little negative effect on the Young's modulus and cold workability of the Ti-26Nb-4Zr alloy.Aimed at obtaining relatively larger recovery strain, the Ti-18Nb-9Zr(at.%) for superelastic application is selected. Effect of Zr content on the martensitic transformation of the Ti-18Nb-XZr(X=0,3,6,9) alloy is characterized. Microstructure of the as water quenched Ti-18Nb-9Zr alloy after800℃for0.5h solution treated is composed of retained β matrix and a certain amount of a"martensite, while the other three Ti-18Nb-XZr (X=0,3and6)alloys have a single a"martensite microstructure. No trace of athermal ω phase is found in any of the as-quenched alloys. Ms of the Ti-18Nb-XZr (X=0,3,6and9)alloys decreases nonlinearly as the Zr addition increased from3%to9%. Ms of Ti-18Nb-9Zr alloy is determined to be around room temperature.Effect of cold rolling and subsequent heat treatments, including solution and annealing, on phase constitution and superelastic behavior of Ti-18Nb-9Zr alloy is characterized at room temperature. As-quenched Ti-18Nb-9Zr alloy shows superelastic behavior, however the recovery strain is less than1%. Isothermal ω phase precipitated during low temperature annealing could not improve the superelasticity. Superelastic behavior is observed in some intermediate temperature annealed specimens. Annealed at550℃for10minutes, the superelastic behavior is perfect in the second cyclic loading-unloading tensile test and the maximum recovery strain of2.8%is obtained at the third cyclic tensile test at the loading strain of3%.(3phase stability is the decisive factor influences the superelasticity of the Ti-18Nb-9Zr alloy at room temperature.
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