NDR is an acronym: Nanograin Damage Resistant. NDR is a process which comprises a thermal-mechanical treatment designed to produce nanoscale microstructural refinement. This refinement is evidenced by a significant increase in the material’s ability to resist damage during high cycle mechanical loading, as encountered, for example, during the service of a long-term cardioverter defibrillator lead implant due to pulsating stresses.
The NDR process may be applied to non-precipitation hardening, non-sensitizing, implant-grade alloys such as those called out by ASTM F562 alloy (35N LT wire or MP35N wire), ASTM F1058 (FWM 1058 wire) and ASTM F138 (316LVM).
NDR processing does not change the chemical or atomic makeup of the parent alloy system. Properties such as density, electrical resistivity, thermal conductivity and thermal coefficient of expansion are similar before and after the application of NDR technology.
The performance of NDR wire is attributable to the underlying microstructure. Conventional microstructure is shown below (left), where the average breadth of each grain is 2 microns. The next image (right) shows NDR-refined microstructure where similar features are on the order of 200 nm.