Comparison of various preparation methods of binary NiTi-shape memory alloys

The visualization of the "true", i.e. unaffected microstructure by means of a metallographic profound preparation is particularly challenging for the nickel-titanium-alloy (NiTi) since under mechanical preparation it forms deformation and smear layers and due to its corrosion resistance it is not attacked by most acidic and alkaline solutions.

Additionally the used samples of this material are mostly wires with small diameters of 0.5 mm to 2.0 mm for actuator constructions in industry resulting in the necessity of a more elaborated sample handling.

In literature several preparation routines are presented for NiTi-alloys. Whereas some routines are more effective than others some preparation methods will also lead to false results. Especially in the course of the characterization of the influence of the processing parameters and the service conditions on the microstructure of these alloys an unfailing preparation is crucial.

In this study we will compare the results of various selected mechanical and electrolytic preparation methods concerning the successfullness of the visualization of the microstructure of nitinol. Besides showing the successful preparation methods we will also discuss artifacts and false strikes, to give a deeper understanding of the preparation of nitinol.