Industrial computed tomography (CT) enables the non-destructive three-dimensional representation and measurement of workpieces. Due to its high flexibility, this measurement and analysis method is used both in research and development as well as in production. Applying CT technology, internal structures or shape deviations can be measured and material defects can be detected.

Nitinol is an important material for medical implants due to its super elastic behaviour and since its mechanical properties mimic biological materials. The surface of nitinol implants is commonly covered with a thin titanium dioxide (TiO 2 ) layer which acts both as a passivating layer to increase the corrosion resistance and as a barrier layer to address the toxicological concerns of long-term nickel release into the biological tissue. Even though nitinol undergoes a natural passivation when exposed to air, various thermal, chemical, and electrochemical surface finishing techniques are applied during manufacturing to replace the native oxide layer by uniform TiO 2 layers of controlled thickness. The properties of these oxide layers depend on the surface finishing technique and the process parameters.

Ultrashort pulse (USP) lasers are an established technology to manufacture nitinol medical devices. USP lasers offer a great variety of processing parameters which can be utilized for fine cutting, laser lathe and ablation of nitinol. Usually, several hundreds of kHz are used to penetrate the material with pulses of fixed energy and frequency. New USP laser sources are offering a so-called burst mode which can be used to precisely control the energy deposition into the material by adjusting the temporal pulse distribution. Depending on the applied process parameters, this leads to a cut through or ablation of some material besides a modification of the irradiated surface. Previous work showed that the bulk material is not affected by such laser light whereas the laser-matter interface is changed. The perpendicular irradiated surfaces are dominated by laser-induced periodic surface structures (LIPSS) which are oriented to the direction of polarization of the laser beam and by cone-like protrusions (CLPs). These modified surfaces allow, e.g., different roughness, wetting, corrosion, bioactivity, and ultimately tribological properties. The effect of such femtosecond laser-generated structures was shown for stainless steel and titanium. Complex medical devices might benefit from locally adjusted surface properties e.g. reduced frictional force between tissue and device or improved adhesion due to an increased surface area through microstructures.

Advanced micromachining processes like laser micromachining, electric discharge machining (EDM) and milling are key processes when fabricating Nitinol medical devices. Unfortunately, each machining process alters the thermomechanical properties of Nitinol - especially around the processing zone. To judge how much this affects the functionality of Nitinol devices, precise knowledge about the micromachining processes applied is crucial. Performance of a medical device from a manufacturer point of view is governed by its geometry. Attainable geometries are linked to the respective machining technology. Lastly the process itself might be limited concerning surface roughness, contour accuracy, and aspect ratio. Ecological aspects include the achievable material removal rate (MRR, volume per time) and necessary post processes. In this work, the authors report on recent developments in the field of micromachining Nitinol, especially in which way the respective technology affects the properties and the design of medical components. A comparative analysis of micromachining technologies is presented.

Nitinol's thermomechanical properties are well studied and understood below the so-called martensite death (MD) temperature, above which martensite cannot be induced by mechanical stress: Even at high stresses Nitinol stays in the austenite phase. This paper presents tensile tests performed well above MD (>150 °C) with Nitinol specimens laser cut from tube. The investigations show that Nitinol drastically changes its mechanical properties in this temperature range: The superelastic plateau shortens and finally vanishes. Furthermore, Nitinol starts becoming more ductile.