Limitations on leveraging Af to predict the mechanical response of Nitinol

Tuesday, May 14, 2019: 10:15 AM
K2 (Bodenseeforum Konstanz)
Dr. Daniel Janda , W.L. Gore & Associates, Flagstaff, AZ
Christopher C. Lasley , W.L. Gore & Associates, Flagstaff, AZ
Tailoring the Af temperature for implantable medical devices is one of the major considerations when selecting process parameters for Nitinol components. Besides enabling a superelastic response under in vivo conditions, Af is often correlated to mechanical properties such as tensile behavior and fatigue performance. Measuring Af of Nitinol components is relatively simple in contrast to mechanical testing and therefore it can be convenient to monitor process fluctuations by periodically measuring Af. However, the practice of tailoring heat treatment process parameters to achieve specific Af temperatures can result in undesirable mechanical behaviors of the Nitinol component. Experimental data will be presented demonstrating how a single lot of medical grade Nitinol wire can be heat treated to achieve similar Af temperatures but exhibit large variations in tensile response and fatigue life. The limitations of leveraging Af temperatures to estimate mechanical properties will be demonstrated and discussed.
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