New Processing technologies for high radial-force stents by Ti-50Ni alloys
Kiyoshi Yamauchi
Tohoku University, 6-3 aoba Aramaiki Aoba-ku, Sendai, Japan
yamauchi@material.tohoku.ac.jp
Masahiro Yamamoto Seiichi Takamura
JAROC CO., LTD , 22-1 Simokogita-cho, Fukui, Japan
yamamoto@jaroc.co.jp takamura@jaroc.co.jp
Keywords: shape memory alloy, super-elasticity, Ti-50Ni alloy’s stents
Abstract: Ti-Ni alloys show shape memory effect(SME) and super-elasticity(SE) with the thermoelastic martensitic transformation, and are used in a wide range of fields such as automobiles, home appliances and medical devices. Its property depend on Ni contents and Ni rich Ti-51at% Ni alloy having SE at shape recovery temperature (Af) ≤ 37 ºC are used for interventional Radiology( IVR) devices such as stents and guide wires. Ti-50Ni alloy with Af > 37 ºC are difficult to obtain SE at body temperature, so that’s are considered unsuitable for IVR and used mainly for industrial actuator application.
Stents are used to prevent vascular restenosis after operation, and SE type application have been expanding to peripheral. Here, the problem of SE stent is its downsizing, and the solution is the development of high stiffness core. The commercially available Ti-51Ni alloy is subjected to 500 ºC treatment for straightening. Since this treatment temperature is near the recrystallization temperature of Ti-Ni alloys, the stiffness of stent is decreased. The Ni-rich precipitates such as Ti3Ni4 phase which are considered to be breakage factor are inevitably decomposed in the parent phase matrix of the Ti-51Ni alloy.