Study On The Preparation, Thermal-mechanical Processing Technique And Surface Bioactivity Of Novel Titanium Alloy For Biomedical Applications

This paper studied the preparation, thermal-mechanical processing technique and surface bioactivity of Ti-25Nb-2Zr (at %) alloy. The influence of small amount of Zr element to phase transformation, microstructure, mechanical properties and shape memory effect were examined by means of DCS, optical microscopy, XRD, tensile test, microhardness test, shape memory effect and superelasticity test. The relationship between microstructure, mechanical properties of Ti-25Nb-2Zr alloy and heat treatment and cold work technique was further studied. Meahwhile, the surface of Ti-25Nb-2Zr alloy was modified by oxidization in air. The surface of modified and subsequently immersed in Ca-P solution alloy were characterized by SEM, EDS, XRD, XPS and FTIR. After experiment and theoretical study, the following results are listed as follows:The addition of small amount of Zr element in Ti-25Nb alloy could lowerβtransus, prohibit precipitation of phase and refine its microstructure. Especially, the phase transformation temperature could be lowered by 10 K with addition of 1at% Zr element. The strength of Ti-25Nb alloy initially increased with increasing Zr content, and then it decreased with further addition of Zr element; while the migration trends of elastic modulus and microhardness with increasing Zr content are the opposite of that of the strength. The highest ultimate strength was obtained with 3at% Zr addition while the lowest elastic modulus was get by 2at% Zr addition. The addition of Zr element could influence the Ms of Ti-25Nb alloy. The alloys with 2at% Zr content could precipitate martensite when deformed in room temperature, so the shape memory effect of this alloy is more evident than other alloys.When Ti-25Nb-2Zr alloy was solution treated aboveβtransus, its phase structure retained fullyβphase with low strength and superior plasticity. As solution temperature rised, the microstructure get coarser which lead to the decrease of its strength and plasticity. When aged at 350℃,ωphase appeared in the the alloy; when aged at 450℃, phase emerged in the alloy. When the alloy was cold rolled, stress induced martensite transformation emerged in the alloy. Because of the co-work of martensite transformation and work hardening, the harden effect of the alloy was not obvious when the amount of cold work was small. When Ti-25Nb-2Zr alloy was oxidized in air, the surface oxide of the alloy transform first from metastable titania to anatase, then to stable rutile. When the alloy was oxided in air at 500℃for 2h, SEM and AFM observation showed that the surface roughness of the alloy increased evidently. When the specimen oxidized at 500℃for 2h was immersed in Ca-P solution, Ca-P layer was successfully prepared in the surface of the alloy. XRD analysis showed that the main content of the Ca-P layer was hydroxyapatite. XPS and FTIR analysis showed that CO32- ion existed in the Ca-P layer.