MICROSTRUCTURAL CHARACTERIZATION OF NITINOL STENTS
 

A. Toro¹, W. Van Geertruyden², W.Z. Misiolek³, X.D. Han⁴ and M.H. Wu⁵

 

1. National University of Colombia, Medellin, Colombia
2. EMV Technologies, LLC, Bethlehem, PA, USA
3. Institute for Metal Forming, Lehigh University, Bethlehem, PA, USA
4. Solid Microstructure & Property Research Institute, Beijing University of Technology, Beijing, P.R. China
5. Memry Corporation, Bethel, CT, USA

 

Abstract

 
Nitinol self-expanding stents are widely used in peripheral vascular interventions.  These stents are generally manufactured from Nitinol tubing by laser micro-machining, followed by shape setting and electropolishing. A detailed study of the microstructural features in NiTi stents was performed, which included crystallographic texture analysis as well as TEM examination to determine the grain structure and precipitation kinetics. The samples were extracted from vascular stents, as well as from the parent tubes. Care was taken to avoid changes in the microstructure derived from mechanical polishing during the specimen’s preparation for EBSD observation, while the Focused Ion Beam (FIB) equipment was used for preparation of TEM discs. The specimens were analyzed at different stages of the stent production process, and correlations between the microstructure and the manufacturing process were established. Characterization of the main morphologic features of various phases was based on TEM imaging, and the effect of the different processing steps on the crystallographic texture was determined by adequate selection of samples location.
 
 
Key Words:  Nitinol stent, stent manufacturing, laser cutting, texture, microstructures.