Surface Treatment Dependent Corrosion Resistance Of Nitinol Wires After Deformation

The widespread application of Nitinol for medical implants implies a comprehensive understanding of potential damage mechanisms in vivo. Regarding corrosion, the surface composition and integrity are expected to have a major influence on the chemical resistance of the implants in situ and consequently on their mechanical functionality. The aim of this work is to analyze the corrosion resistance of different Nitinol surfaces for medical implants after plastic deformation. The results help to estimate how deformation as it might occur during manufacturing or implantation, affects the corrosion resistance of respective implants.

For our investigations, Nitinol wires of medical quality with different surface treatments were manufactured and plastically deformed under tension. We applied scanning electron microscopy and transmission electron microscopy for determining plastic deformation and visualizing remaining cracks after unloading. The composition of the different surfaces was analyzed by means of glow discharge optical emission spectroscopy using similarly treated Nitinol sheets.

Finally, the corrosion resistance with respect to each surface treatment was determined by means of cyclic potentiodynamic polarization tests according to ASTM F2129. We chose the total surface area being corrosion tested according to suitable implants manufactured by ADMEDES GmbH.