Ingot to Stent Part I – Microstructural and Corrosion Evaluation of Modern Nitinol Grades

Abstract For producers and end-users of high-performance Nitinol, a material that functionally depends on everything that is done to it, it is critical to keep pace documenting the connection between producer-evolved grades and critical subcomponent performance. In Nitinol, the latitude of the industrial standard material specification ASTM F2063 should be continuously plied, and performance outcomes weighed against end-use demands as an aid to relevant use recommendations and requirements development. The current standard specification for wrought NiTi requires maximum oxygen and carbon levels of 400 ppm and maximum observed contiguous particle- void-assembly (PVA) lengths not exceeding 39.0 microns measured in longitudinally mounted specimens. Performance variation across impurity- and PVA length-compliant nitinol grades, especially with respect to structural fatigue, is well documented where each new study gives a snapshot in time that depends on initial chemistry and PVA distributions, processing history, test coupon geometry, fatigue test boundary conditions, and other factors. This study is a small step toward keeping pace with the connection between nitinol grades and tubing performance.