Assessing the corrosion behaviour of Nitinol for minimally-invasive device design

Abstract

SummaryNitinol is a very attractive material for manufacturing minimally-invasive therapy devices and tools because of its unique superelasticity and shape-memory properties. While several studies have shown it to possess good biocompatibility, its high nickel content and possible dissolution during corrosion still remain a concern . However, passivation and electropolishing can significantly decrease nickel dissolution from Nitinol by forming a corrosion-resistant titanium oxide surface layer. In general, passivated and electropolished Nitinol exhibits equivalent, if not better, static corrosion behaviour and ability to resist and repassivate (repair) surface damage when compared with 316L stainless steel (SS). Combining Nitinol with SS, titanium and tantalum does not significantly affect its corrosion behaviour. However, combining Nitinol with gold, platinum and platinum-iridium alloy can result in an order of magnitude increase in corrosion rate. Nickel release from Niti nol decreases from well below dietary levels to nearly non-detectable levels in the first few days following immersion in a physiological medium. Finally, in vivo studies indicate minimal corrosion of Nitinol during im plantation, with released nickel concentration in surround ing tissues or organs being equivalent to that released by 316L SS.

Influence of surface layer on mechanical and corrosion properties of nickel-titanium orthodontic wires

“…It is common to perform in vitro studies of corrosion processes using electrochemical methods [5][6][7]17,18,21,22 because the release of metal ions within the oral cavity occurs over a long period and is associated with discoloration of adjacent structures and teeth as well as allergic and toxic reactions. 14,15 Electrochemical impedance spectroscopy (EIS) testing determines the polarization resistance, a direct measure of corrosion resistance; cyclic polarization testing helps in the observation of the pitting tendencies of the alloy; and in vitro anodic polarization studies simulate the natural corrosion mechanism that usually happens over a protracted duration of time.…”

Effect of chemical etching and aging in boiling water on the corrosion resistance of nitinol wires with black oxide resulting from manufacturing process

“…It should be pointed out that treated wires exhibited a Ti-like behavior in both potentiodynamic and potentiostatic tests, but behavior inferior to titanium and similar to that of stainless steel in scratch tests. 24,25 The well-known reactivity of titanium is probably the major cause of its high scratch repassivation capacity, though microstructural homogeneity is also a factor of great importance. If the possibility of the removal of precipitates from the surface of Nitinol is real due to the series of surface treatments and exposure to corrosion tests, a microstructurally homogeneous Nitinol surface may result.…”

Formation of Ni-Ti intermetallics during reactive sintering at 800–900 °C

“…[6][7][8] The most commonly applied techniques in the industrial production of nitinol alloy are melting metallurgy processes -vacuum induction melting (VIM) and vacuum arc remelting (VAR). 9,10 In the VIM of Ti-containing alloys there is a serious danger of a strong contamination of the melt due to the high reactivity of molten titanium. 11 The VAR technique makes it possible to prepare alloys of higher purity, but there is a problem with homogeneity.…”