Characterization of Laser-Generated Surface Layers: Heat-Affected Zone (HAZ) and Recast

Laser cutting can be seen as one of the crucial processes to manufacture Nitinol medical devices. Three different laser types constitute the current industry standard: YAG, Fibre and Ultra Short Pulse. Besides the translation of a desired stent pattern into semi-finished material like tubing, laser cutting also generates performance-fading surface layers. Therefore a comprehensive understanding of laser cutting process outputs such as recast layer and heat-affected zone (HAZ) formed by the laser is essential.

The focus of this study will be heart-valve-frame-sized Nitinol tubing structured with a single-slot cutting pattern by a state-of-the-art fibre-laser fusion-cutting process. 

With this comprehensive investigation a literature review, recast layer and HAZ characterization as well as an evaluation of the driving laser process parameters, which are responsible for their generation, are performed.

In addition metallographic sectioning, focused ion beam microscopy and electron backscatter diffraction (EBSD) are used as microstructural and crystallographic characterization methods.