Thin Wall SMA Composites: Where Plating Will Not Apply
J.E. Schaffer, Ph.D., Senior Research and Development Engineer & D.L. Snider, DFT Process Engineer
You may know that Fort Wayne Metals has been in the business of providing effective DFT® composite wire solutions for more than 30 years into industries such as cardiac pacing and neurovascular stenting. DFT wires are commonly ordered with a specific area fraction (%) of another metal, like silver for conductivity (e.g. 35N LT-DFT-28%Ag), or platinum for x-ray-opacity (e.g. NiTi-DFT-10%Pt) – these DFT wires with less than 50% area core fractions are known as thick wall composites. Sometimes a thick wall composite may preclude the very design intent. For example, thick metallic coatings over Nitinol can completely mask its elastic capabilities in all loading modes, and yet, metallic coatings can provide tremendous benefit in some applications. One such example is when a high conductivity or extremely corrosion resistant surface is needed. Plating does not easily apply to Nitinol, but we have figured out how to adapt the DFT process to produce smooth, bright, and concentric “coatings”. Shell layers, such as gold and platinum, can be drawn over wire to achieve thicknesses under 200 nanometers in ultrafine wire (0.100 mm). Many other composite designs are under active investigation within FWM Research & Development. For more information, please contact: [email protected].
Figure 1 – SEM wire-sections showing (a) Superelastic, Platinum-DFT®-95%NiTi#1 comprising an outside diameter of 0.050 mm with a 0.50 micron coherent and highly concentric pure platinum shell; (b) Solid superelastic 0.05 mm NiTi#1 wire; Stress-strain response of (c) Heat straightened Pt-DFT®-95%NiTi; and (d) Heat straightened NiTi#1 (Ti-50.8 at.%Ni)
Disclaimer: Our monthly highlights are sneak peeks of what our R & D department is working on. This does not mean we have what is referenced above ready for manufacturing.
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