Fiber Laser Generated Surface Layer Characterization: Heat Affected Zone (HAZ) And Recast Layer

Laser cutting of nitinol during the production of medical devices is a very demanding process regarding many aspects. Local heating, resulting especially during fiber laser fusion cutting, changes the material’s mechanical properties. This process critically affects the material and has to be kept under close supervision. Depending on the local temperature during laser cutting, different types of microstructures can be observed: non-affected bulk material (T_Material < T_{Recrystallization}), heat-affected zone (T_{Recrystallization} < T_Material < T_Melting) and recast/dross (T_Material > T_Melting). The focus of this study is a quantitative investigation on the formation of these microstructures during fiber laser cutting.

For that purpose, the laser and process parameters (e.g. laser power, beam caustic, process gas, water flow) as well as the cutting strategy are varied to reveal their influence on the material after cutting (as-cut). Furthermore, geometric features of the specimen such as tip radius or strut width are varied to estimate the impact of the product design.

The microstructure of the as-cut material will be analyzed via the size measurement of the different material zones after metallographic sectioning. The distinction between the previously mentioned types of microstructure can be recognized based on their corresponding grain sizes and geometries.