Study On Fabrication And Properties Of Biomedical Near β-type TLM Titanium Tubes

Vascular stent has become one of the most effective ways to cure the cardiovascular and cerebro vascular diseases with the widely application and development of the minimally invasive treatment. At the same time, the β-type titanium alloy is becoming a focus of percutaneous transluminal coronary angioplastry research due to its excellent biocompatibility and the lower elastic modulus. Therefore, preparation α β-type titanium alloy tube used for cardiocascular stent is particularly important. However, besides the requirements of good biocompatibility, excellent mechanical compatibility and elastic properties are also needed to ensure its function in the lesion positions. The excellent mechanical is reflected mainly in sufficient radial strength and excellent axial flexibility, the matching between which lead to better accommodate to the environment.Near P-type TLM (Ti-25Nb-3Zr-3Mo-2Sn, wt%) alloy is a new biomedical titanium alloy which designed based on d-electron alloy theory and the principle of equivalence Mo. TLM alloy tubes with Φ8.0×1.0mm were rolled by cold-roll, and Φ4.0×0.3mm tubes with small diameter and thin-wall were successfully prepared by the process in this paper. The microstructure evolution, phase composition and mechanical properties were analyzed in this study. Cold-rolled Φ4.0×0.3mm tubes were solution treated (ST) in different temperature of660-750℃. Moreover, the samples solution treated at660and720℃were selected for subsequent aging treatment (AT) at510℃with different time. The effect of heat treatment on microstructure, mechanical properties and elastic properties of tubes were analysied. The main results are summarized as follows:TLM titanium tubes of Φ4.0×0.3mm can be fabricated by the cold-rolling and intermidate annealing, under a controlled small deformation rate. The microstructure of the cold-rolled tubes are equiaxed β grains and small amount of stress induced a"(SIMa"), the stress-strain curve shows a grandual strain hardening with the larger elastic range of3%. The microstructures of annealed tubes are singleβ phase with equiaxed grains, the stress-strain curve of which showes a clear "double yielding". The first yielding corresponding to the beginning of β→SIMa" transformation. Because of the reversible transformation of SIMa", the annealed tubes have excellent super-elasticity. At the same time, both states show ductile fracture characteristics. The texture component for cold-rolled and annealed tubes are all {111}<110> and {223}<110> in the rolling direction.The microstructures of ST-states are equiaxed β grains. The average grain size increases with the increased solution temperature. ST-states obtained from solution treatment above the transus temperature is composed of β+α", while that of ST-state at660℃contains a small amount of a-phase. Comprehensive analysis shows that Rpo.2:443MPa, Rm:626MPa, A50mm:27.5%, E:72.5GPa, therefore, the tube obtained from720℃-ST has a good overall mechanical performance.During the aging, needle-like a-phase mainly precipitates at the grain boundaries. The precipitation rate of a is higher after660℃-ST, As the aging longer than3h, a-phase precipitation leads to "double yield" feature disappearing. The tensile strength and elastic modulus increased but the elongation decrease with the delayed aging.The total recovery strain ratio (R) and the recovered strain ratio (S) were decreased with the amount of pre-strain increased. The AT-state has the higher R value, cold-rolled state follows, and the ST-states are relatively poor. The order of S is AT-state, ST-states and cold-rolled state, while the difference between ST-states is relatively small. In contrast,690℃ST-state has a relatively good R and S values; Short time(1h) aging can improve R and S value for the720℃ST-state, and the R and S value will decrease when aging at the longer time (3h,6h). Aging time (1h) has an adverse effect on the value of R and S for660℃ST-state. Elastic modulus of the three states will decline with the increased pre-strain, among which the largest drop up to20GPa.