Shot Peening Process Optimized for Nitinol Medical Devices

Shot peening, a surface treatment that generates compressive residual stresses, can significantly improve the fatigue life of metal components. For medical applications, contamination and lack of biocompatibility of the peened surface can be a challenge.

For this study, a process sequence was developed specifically for medical devices made from Nitinol. The process involves shot peening with a ceramic media followed by chemical and electrochemical processing steps to remove embedded particles and passivate the surface.

Material removal during chemical processing was tightly controlled to ensure that the layer of compressive residual stresses created during the peening process remained intact, while resulting in a smooth, debris free surface. Combined, the peening and controlled material removal processes produce a final product with significantly improved fatigue behavior and superior biocompatibility when compared to untreated Nitinol.