The Production of a Thin Wire of Ti-Nb-Ta-Zr Shape Memory Alloy for Medical Devices

Alloys possessing a shape memory effect and mechanical characteristics similar to the behavior of living tissues have been already used for years as the material for production of medical devices, including implants, for example stents, without the need for additional devices except catheter-carrier. However, most of these alloys contain elements (including on its surface) which is toxic for organism. To satisfy the requirements of biochemical compatibility, the alloy should contain only safe elements as alloy components, which include: Ti, Nb, Ta, Zr. The possibility of obtaining of Ti-Nb-Ta-Zr thin wire was investigated. The structure was determined with the use of the optical microscope, X-ray diffractometer, scanning electron microscope (SEM) and Auger spectrometer. Optimal conditions for smelting were chosen. It was noted that a uniform structure was obtained for all compositions, before and after homogenizing annealing. The ingots have a dendritic structure. Niobium and zirconium were uniformly distributed throughout the sample, tantalum was concentrated in the dendrites themselves, titanium was predominantly in the regions between the dendritic axes, but is also found in it. X-ray diffractometry indicates that the elements of the alloy were not distributed in it by separate fragments, but were united in a single structure. The optimal annealing temperature of Ti-(20-30)Nb- (10-13)Ta-5Zr alloys was noted in the range from 600 to 900°C. The grain boundaries after plastic deformation and heat treatment were not identified in a microstructural analysis, which indicates that there was no recrystallization. It is possible that nanostructure was formed. The morphology of wires of any composition after drawing shows a high heterogeneity, two types of surfaces of different composition alternate - areas with a high content of carbon and with a high content of oxygen were observed. After mechanical treatment the surface, its uniformity increases.