High-Precision Surface Analysis of NiTi by Glow Discharge Optical Emission Spectroscopy

The variability of structure and properties of the oxidic (among others) surface layer on NiTi allows for designing it for optimized behavior, e.g. for medical applications with controlled release of Ni or improved fatigue properties. Precise knowledge of elemental distribution in the near surface region is a major aspect for understanding formation processes, designing novel surface properties or advancing the current standards of quality management. Until present, particularly X-ray Photoelectron Spectroscopy, Auger Electron Spectroscopy or Rutherford Backscattering have been applied as experimental techniques for characterizing NiTi surfaces. However, all of the techniques have their individual shortcomings, e.g. duration of measurement, complexity of interpretation or limited depth resolution.

In the present work, conditions necessary for swift and highly precise characterization of NiTi surfaces by Glow Discharge Optical Emission Spectroscopy (GDOES) are presented. It is shown that careful calibration of the technique allows for measuring elemental distribution at and below the surface of NiTi with a level of detail that exceeds the results documented in the literature. For surface layers with thicknesses from the low nm to the µm range, meaningful and reproducible results are attained. It is exemplarily discussed how these results can help to understand the surface layer formation on NiTi. Additionally, the recently discovered ability of GDOES for metallographic microstructure preparation of NiTi is presented.