SHAPE MEMORY ALLOY ARTICLES WITH IMPROVED FATIGUE PERFORMANCE AND METHODS THEREFORE

摘要

Articles made of shape memory alloys having improved fatigue performance and to methods of treating articles formed from those materials by pre-straining the articles (or desired portions) in a controlled manner so that the resultant articles exhibit improved fatigue performance. The shape memory articles are preferably medical devices, more preferably implantable medical devices. They are most preferably devices of nitinol shape memory alloy that is superelastic at normal body temperature. The pre-straining method of the present invention includes the controlled introduction of non-recoverable tensile strains greater than about 0.20% at die surface of a desired portion of a shape memory alloy article. Controlled pre-straining operations are performed on shape-set nitinol metal to achieve non-recoverable tensile stra in greater than about 0.20% at or near the surface of selected regions in the nitinol metal article. The pre-straining operations result in a significant increase in fatigue life of the selectively treated regions and an overall improvement in the fatigue performance of the device.