Evaluation of the Surface of Nitinol after MR Polishing Process

Nitinol is used in various industries, especially for biomaterials. Generally, the surface integrity of sub-micron level and non-surface flaw is required in nitinol for biomaterial. However, surface flaws, such as scratches, pits, and residual stress, can occur on the polished surface, and it is difficult to remove these surface flaws. The corrosion is accelerated continuously and causes bad influence in the body. Therefore, in this study, conventional polishing and MR polishing were used to minimize the corrosion and residual stress when the nitinol is used as biomaterial. X-ray diffraction and Tafel extrapolation were used to investigate the residual stress and the corrosion, and the strain hardening was investigated by nanoindentation. Surface integrities were also evaluated by SEM image and surface roughness results. As a result, the increased residual stress in conventional polishing was decreased by MR polishing. The result of corrosion test was improved from ?301 mV to ?280 mV. The residual stress was improved from ?38.18 MPa to ?31.17 MPa. Finally, it is certified that MR polishing can be used to minimize surface flaws and to improve the corrosion properties.