Nitinol Microstructural Characteristics Analyzed by Combined Focused Ion Beam and Scanning Electron Microscopy

Nitinol, being the most established shape memory engineering material, has been subject to a number of different improvements during its use in industry – particularly with respect to material microcleanliness and surface quality. Various process developments have led to improved semi-finished Nitinol product, like wire, tube or sheet, and to finished components that are more durable, for example with respect to fatigue or corrosion.

In parallel to material development, instrumentation for materials analysis has also seen significant progress over the decades of Nitinol industrial use. This work shall illustrate the possibilities of state-of-the-art materials analysis of Nitinol employing combined focused ion beam (FIB) / scanning electron microscopy (SEM) together with sophisticated signal detection techniques, like electron beam backscatter diffraction (EBSD).

Using a Zeiss Crossbeam 540 FIB/SEM with field emission source, combined in-lens secondary/backscattered electron detector and EBSD detector, various Nitinol microstructural characteristics are analyzed using simultaneous FIB preparation and SEM visualization: assemblies of nonmetallic inclusions and voids (“stringers”) are visualized for various Nitinol material qualities; local interaction of inclusions with different surface oxide qualities is investigated; heat-affected zone (HAZ) from laser cutting is analyzed using EBSD and Nitinol/metal composite materials, like drawn filled tube (DFT) wires are studied with respect to Nitinol microcleanliness.