Innovative Technology for Preparation of Seamless Nitinol Tubes Using SHS Without Forming
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Ni-Ti alloys known as Nitinol with properties like superelasticity and pseudoplasticity find their use in medical applications,[1–3] stents for unblocking of body conduits, orthopedic implants, and in dentistry, biomedical, and surgical instruments.[4–6] Other applications are sensors, actuators, structural connectors, and vibration dampers in technical area.[2] In many applications, Ni-Ti alloys are used in forms of thin wires, helical springs, thin walled tubes, ribbon, thin films,[7] surgical stents,[1] perforated plates,[8] or holed structures.[9,10] These forms are achieved by forging, rolling, drawing, hot and/or cold plastic deformation, and other final machining processes.[11] Melting metallurgy, cold/hot working, and following machining are the most often used production processes nowadays. The machining is difficult due to specific properties of the material and surface oxide layer. Nitinol can be machined using conventional techniques such as milling, turning, and drilling. Laser cutting, electric discharge machining (EDM), photo-chemical etching, and water jet cutting seem to be good machining processes.[9,12] Laser cutting and PAVEL SALVETR, ZUZANA PECENOVA´, ANDREA SˇKOLA´KOVA´, and PAVEL NOVA´K are with the Department of Metals and Corrosion Engineering, University of Chemistry and Technology, Technicka´ 5, 166 28, Prague 6, Czech Republic. Contact e-mail: [email protected] Manuscript submitted September 10, 2016. Article published online January 25, 2017 1524—VOLUME 48A, APRIL 2017
machining is the preferred method for creating stents from Nitinol tube.[13] Self-propagating high-temperature synthesis (SHS) is one of powder metallurgy methods, which produces Ni-Ti alloys or other materials reliably.[14–21] It enables to eliminate problems during melting and casting of alloy such as high reactivity of melt, contamination of crucible material during vacuum induction melting. In this work, we developed a process using SHS, which enables easy and fast production of seamless shape memory Ni-Ti tubes. In this process, there is no need for forming and the machining operations are reduced at the same time. The process for production of Ni-Ti tubes with shape memory effect by SHS uses elemental nickel (99.99 wt pct purity, particle size
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