Microstructural Refinement Yields Macro-Level Changes in Fatigue Strength

The medical device industry is changing, providing solutions which are smaller and less invasive, improving performance standards in existing components, as well as developing solutions which are smaller and less invasive.  To achieve all of these goals the industry needs materials that are equally small in size, while also being highly durable. No one material has been able to match the requirements of such a range of devices, until NDR® wire.

Fort Wayne Metals manufactures Nanograin Damage Resistant wire, or NDR® wire, using a patented thermal-mechanical treatment that seeks to produce nanoscale microstructural refinement.

Even in high cycle fatigue conditions, NDR® wire can operate effectively for long periods of time. Its ability to resist damage in high cycle mechanical loading offers resilience in applications that are subject to cyclical stresses over long periods of time, such as long-term cardioverter defibrillator leads.

Improve Fatigue Strength with Refined Microstructures

Fort Wayne Metals typically produces NDR® wire with high performance alloys such as 35N LT®, where refined inclusion sizes work well alongside the refined microstructure. It is this microstructure at the core of NDR® wire that allows for its excellent performance.

The refined grain structure of NDR® wire features an average grain size of just 0.2 microns. The average grain size of typical microstructure is ten times this, at around 2 microns. NDR® wire is therefore able to offer the resilience needed for high cycle mechanical loading[i] through thanks to this nanoscale microstructural refinement.

Mechanical and Physical Properties

Although this refined grain structure in alloys manufactured as NDR® wire provides greater fatigue strength, there is little change to the physical characteristics. Features such as corrosion resistance, radiopacity, and electrical resistivity are akin to those of wire produced via conventional methods.

This allows clients to personalize NDR® wire to their needs while maintaining the majority of standard features, and refining the microstructure for greater fatigue strength.

Mechanical properties are also similar to those of alloys when produced as standard round wire, with minor enhancements in certain tempers. While ultimate strength, yield strength, and rupture strain (elongation) were identical in Hard and Spring conditions, NDR® wire demonstrated greater ultimate strength and yield strength than standard wire in the annealed condition.

It should be noted that, to make the most of the NDR® wire, the material’s temper should be adjusted to suit the specific application, and it is advisable that customers engage in close technical communication with Fort Wayne Metals.

Customize NDR® Wire for Your Application

The greater fatigue strength attained via refined microstructures, as well as NDR® wire’s capacity to preserve mechanical and physical features akin to standard wire, can offer solutions in a broad range of applications.

The unique method employed by Fort Wayne Metals to produce NDR® wire can also be applied to an assortment of implant-grade alloys that are non-precipitation hardening and non-sensitizing, including 35N LT® and MP35N® (ASTM F562), FWM® 1058 (ASTM F1058), 304LV (ASTM A580), and 316LVM (ASTM F138).

It is also possible to produce NDR® wire in a variety of forms aside from standard round wire, including as DFT® wire and flat-rolled ribbon. To support clients aiming to develop smaller, less invasive medical devices, or to enhance the performance of existing components, NDR® wire can offer higher fatigue strength for future medical devices.

References

i. Schaffer, J. "A probabilistic approach to modeling microstructural variability and fatigue behavior in ASTM F562 medical grade wire." Proceedings of the 9th International Congress on Fatigue, Fatigue 2006. 2006.

ii. Comparisons reference conventional and NDR® wire manufactured with 35N LT®, https://fwmetals.com/products/enhanced-solutions/ndr-wire/

For more information on this please visit Fort Wayne Metals.

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