SMST 2017, the Shape Memory and Superelastic Technologies conference and exposition, was held May 15-19, 2017, and Confluent Medical Technologies brought a strong lineup of technical presentations. A common theme was the influence of processing, in addition to material purity, on durability and mechanical performance of superelastic Nitinol components. Slides can all be found at http://nitinol.com. Some have been recorded and posted on the Confluent YouTube channel, and more will be added over the coming weeks. Our talks, in order of appearance:
- The Effect of Low Temperature Aging on Ni-rich Ti-Ni: Presented by Dr. Ali Shamimi
- This talk showed surprising influences on mechanical properties and transition temperatures resulting from heat treatments at low temperatures (100°C – 250°C) and long durations.
- PDF: The Effect of Low Temperature Aging on Ni-Rich Ti-Ni
YouTube: https://goo.gl/caAhDz
- Martensite/R-Phase Superelasticity and Its Implications to Nitinol Durability: Presented by Dr. Tom Duerig
- Reviewing of the mechanisms explained by Ali’s talk, Tom explains the unusual ability to experience superelasticity without involving austenite. This talk introduces “R-M-R” superelasticity (R-phase / Martensite / R-phase) and the implications of this approach for fatigue performance.
- PDF: Martensite/R-Phase Superelasticity and Its Implications to Nitinol Durability
- Effect of Compressive and Tensile Pre-strains on Durability of Nitinol: Presented by Karthikeyan Senthilnathan
- In this talk, Karthik shows computational simulation and experimental evidence demonstrating how strain conditioning (pre-straining) Nitinol components influences durability performance, depending on the polarity of the pre-strain vs. cyclic strain.
- PDF: Effect of Tensile and Compressive Pre-Strains on Superelastic Diamond Surrogate
YouTube: https://goo.gl/hZd8mU
- Volume weighted probabilistic methods for Nitinol lifetime prediction: Presented by Craig Bonsignore
- In this talk, Craig introduces new experimental methods for volumetric quantification of inclusions in standard and high-purity material using sub-micron x-ray computed tomography (XCT). These data are used in combination with new analysis methods to propose probabilistic techniques to predict fatigue durability of superelastic Nitinol components.
- PDF: Volume weighted probabilistic methods for nitinol lifetime prediction
YouTube: https://goo.gl/wcFG6F
Much more detail: Confluent Medical GitHub
- Ultrafast Laser Cutting of Low Mass Superelastic Nitinol Parts: Presented by Dr. Michael Shirk
- Michael presented an overview of pico/femtosecond laser cutting and its benefits relative to conventional laser cutting. Common misunderstanding about the “athermal” nature of this approach are dispelled, with examples of process adjustment that are necessary to produce optimized results for low mass components.
- PDF: Ultrafast Laser Cutting of Low Mass Superelastic Nitinol Parts
YouTube: https://goo.gl/gNssE4
- The Measurement and Interpretation of Transformation Temperatures in Nitinol: Presented by Dr. Tom Duerig
- In this very impactful Friday morning keynote address, Tom explains the importance of measuring martensite reversion (M*) temperature, and the misleading implications of the more commonly specified and measured austenite finish (Af). The Austenite / R-phase / Martensite phase diagram is developed using several experimental techniques, and the previously under-appreciated importance of the triple-point in this is explained, with examples that are relevant to realistic Nitinol medical components.
- PDF: The Measurement and Interpretation of Transformation Temperatures in Nitinol
YouTube: https://goo.gl/CiblkZ
- Correlation of In-vitro Corrosion to In-vivo Corrosion in Nitinol Stents: Presented by Dr. Stacey Sullivan (Confluent’s Daniel Madamba and Christine Trépanier are co-authors)
- Dr. Sullivan of the FDA presented long-awaited results of an in-vivo study created in collaboration between Confluent Medical Technologies and the FDA. In this study, stents were fabricated to have a range of corrosion performance, implanted and survived in animals to study in-vivo corrosion performance. Results showed that implants with a breakdown potential below 200mV experienced localized corrosion in-vivo, and above 600mV showed no localized corrosion, consistent with prevailing industry assumptions.
- Shot Peening Process Optimized for Nitinol Medical Devices: Presented by Owen Falk
- Owen presents results of shot-peening experiments on superelastic Nitinol wire. This study demonstrates fatigue benefits of this process, as well as negative corrosion implications for untreated wire. It is shown that subsequent electropolishing of the surface improves corrosion performance, while retaining some of the fatigue benefits.
PDF: Shot Peening Process Optimized for Nitinol Medical Devices
YouTube: https://goo.gl/4ZnwmJ
- Owen presents results of shot-peening experiments on superelastic Nitinol wire. This study demonstrates fatigue benefits of this process, as well as negative corrosion implications for untreated wire. It is shown that subsequent electropolishing of the surface improves corrosion performance, while retaining some of the fatigue benefits.
- Nitinol With Improved Ductility: Presented by Dr. Behnam Amin-Ahmadi (Confluent’s Ali Shamimi and Tom Duerig are co-authors)
- In this paper, authored by Ali Shamimi, and coauthored by Tom Duerig, Behnam presented results of experiments which demonstrate significant ductility improvements that are enabled by optimized small changes in heat treatment times and temperatures. Transmission electron microscopy (TEM) imaging is used to understand the microstructural mechanisms controlling this effect.
- PDF: Nitinol With Improved Ductility
